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Ultrasonic transducers for medical diagnostic imaging
Abstract
Over the past decades, ultrasound imaging technology has made tremendous progress in obtaining important diagnostic information from patients in a rapid, noninvasive manner. Although the technology has benefited from sophisticated signal processing technology and imaging system integration, much of this progress has been derived from the development of ultrasonic transducers that are in direct contact with patients. An overview of medical ultrasonic imaging transducers is presented in this review that describes their structure, types, and application fields. The structural components of a typical transducer are presented in detail including an active layer, acoustic matching layers, a backing block, an acoustic lens, and kerfs. The types of transducers are classified according to the dimensions of ultrasound images: one-dimensional array, mechanical wobbling, and two-dimensional array transducers. Advantages of each transducer over the other and the technical issues for further performance enhancement are described. Application of the transducers to various clinical imaging fields is also reviewed.
... Ultrasound has been an invaluable tool for medical imaging for decades, and the properties of which have been studied extensively [1][2][3]. However, even as enlightening as the modality has proven to be, there exist numerous limitations such as the static configuration and number of transducer elements [2,4,5], and operator nuances leading to potentially inaccurate or inconsistent measurements [6,7]. ...
... Ultrasound has been an invaluable tool for medical imaging for decades, and the properties of which have been studied extensively [1][2][3]. However, even as enlightening as the modality has proven to be, there exist numerous limitations such as the static configuration and number of transducer elements [2,4,5], and operator nuances leading to potentially inaccurate or inconsistent measurements [6,7]. Furthermore, conventional ultrasound transducers are typically arrays of elements numbering on the order of hundreds for linear arrays to thousands for 2D arrays [2,5]. ...
... However, even as enlightening as the modality has proven to be, there exist numerous limitations such as the static configuration and number of transducer elements [2,4,5], and operator nuances leading to potentially inaccurate or inconsistent measurements [6,7]. Furthermore, conventional ultrasound transducers are typically arrays of elements numbering on the order of hundreds for linear arrays to thousands for 2D arrays [2,5]. This is orders of magnitude smaller than the number of elements in typical optical imaging systems, which commonly employ megapixel-scale resolutions. ...
A new method of generating potentially arbitrary photoacoustic wavefronts with optical holograms is presented. This method uses nanosecond laser pulses at 1064 nm that are split into four time-delayed components by means of a configurable multipass optical delay apparatus, which serves to map the pulses onto phase-delayed regions of a given acoustic wavefront. A single spatial light modulator generates separate holograms for each component, which are imaged onto a photoacoustic transducer comprised of a thermoelastic polymer. As a proof of concept of the broader arbitrary wavefront construction technique, the spatially- and temporally-modulated holograms in this study produce a phased array effect that enables beam steering of the resulting acoustic pulse. For a first experimental demonstration of the method, as verified by simulation, the acoustic beam is steered in four directions by around 5 degrees.
... High-frequency ultrasonic transducers have been developed for highresolution imaging applications, such as nondestructive testing and medical diagnostics. The transducers have a major role in medical applications like ultrasonic diagnosis because they receive electric signals and transmit ultrasonic echoes [1][2][3]. They are composed of a vibrating piezoelectric material that generates mechanical ultrasonic waves. ...
... Poisson's ratio (v) can reflect good information about the material structure variation as a result of any induced factor (such as concentration, temperature, pressure, and so on) [3] (Fig. 14). It is related to the ultrasonic velocities (longitudinal, C L and shear, C S ) according to the following formula: ...
... From the previously obtained results of the prepared alkali borate glasses' properties, they can be used in a new application as passive materials in ultrasonic transducers. Passive materials are used in the fabrication of ultrasonic transducers, like the matching layer, backing layer, and transducer lens [3]. The transducer lens is used in most medical applications that use ultrasonic transducers for diagnostic or imaging purposes. ...
... incorporating directional information. [11][12][13][14] In fields such as underwater sonar, 15,16 medical imaging, 17,18 and nondestructive testing, [19][20][21] phased array techniques and beamforming methods have been successfully utilized to improve target detection. These methods enable sensors to extract directional information, which we expect to significantly improve target discrimination in the automotive domain as well. ...
... Ultrasonic array sensors are commonly used in underwater sonar, 15,16 non-destructive testing, 19,20 and medical sonography. 17,18 However, automotive ultrasonic sensors are considerably less expensive, and due to the high cost pressure in the automotive industry, the potential number of transducer elements in the sensor design is limited. Thus, we employ a small 2 Â 2 elements phased array in our experiments. ...
Current park pilot systems are based on ultrasonic surround sensing and, thus, depend on the performance of ultrasonic sensors. Not only capturing the distance to obstacles but also classifying objects is crucial for advanced driver assist systems and ultrasonic perception. However, current single-element sensors are constrained in classification performance due to a lack of directional information that they are able to capture. In this study, we propose replacing the conventional single-element sensor with a small 2 × 2 array sensor to increase object classification accuracy. The array sensor enables the incorporation of directional information, enhancing target discrimination, even in the compact design of 2 × 2 elements. Further, we propose an efficient convolutional neural network (CNN) to classify preprocessed transducer signals based on experimental data. Several feature extraction methods using the delay-and-sum beamformer, minimum variance distortionless response beamformer, acoustic source maps, and an end-to-end approach are evaluated. Promising classification accuracies are achieved for the array sensor when feeding both the preprocessed transducer signals and an acoustic source map into the CNN, significantly outperforming the conventional single-element sensor. Ultimately, this paper demonstrates the potential of enhancing object classification in ultrasonic surround sensing using small aperture array sensors and leveraging directional information.
... Design choices: Besides deciding between imaging and Doppler configurations, designing sound-based systems requires considerations of frequency, transducer arrangement, beam profile, and source power. Higher frequency results in better axial resolution but has lower penetration depth [34]. 1-D and 2-D arrays are used depending on whether the application requires lateral resolution. ...
... More transducers per unit area increase the lateral resolution but are significantly more expensive to manufacture. A narrower beam profile results in better lateral resolution but sacrifices the field of view [34]. Higher power results in higher SNR but risks tissue damage. ...
Objective:
Rapid advances in cuffless blood pressure (BP) monitoring over the last decade have the potential to radically transform clinical care for cardiovascular health. However, due to the large heterogeneity in device design and evaluation, it is difficult to critically and quantitatively evaluate research progress in cuffless BP monitoring. In this two-part manuscript, we seek to provide a principled way of describing and accounting for the heterogeneity in device and study design.
Methods:
We first provide an overview of foundational elements and design principles of three critical aspects in the pipeline: 1) sensors and systems, 2) pre-processing and feature extraction, and 3) BP estimation algorithms. Then, we critically analyze the state-of-theart methods via a systematic review.
Results:
We find a large amount of heterogeneity in study designs making fair comparisons challenging. In addition, many study designs lead to data leakage, and underpowered studies. We suggest a first opencontribution BP estimation benchmark based on existing public datasets for standardized algorithmic comparisons. Second, we observe that BP distribution in the study sample and the time between calibration and test in emerging personalized devices are significant confounders in BP estimation error. We suggest accounting for these using a metric "explained deviation" which is closely related to the coefficient of determination (R2, a frequently used statistic). Finally, we complement this manuscript with a website, https://wearablebp.github.io, containing a bibliography, meta-analysis results, datasets, and benchmarks, providing a timely platform to understand the state-of-the-art devices.
Conclusion:
There is large heterogeneity in device and study design, which should be carefully accounted for when designing, comparing, and contrasting studies.
Significance:
Our findings will allow readers to parse out the heterogeneous literature and move toward promising directions for safer and more reliable devices in clinical practice and beyond.
... The matching layer is located in the front, which is used to achieve acoustic impedance matching and reduce the reflection of ultrasonic waves at the interface [47]. Among them, piezoelectric materials are indispensable [48]. In this section, we describe in detail the materials used in the focused ultrasonic transducer. ...
... With the development of piezoelectric materials and preparation technology, piezoelectric ultrasonic transducers have been widely used in medical diagnostic imaging. Generally speaking, he image quality of ultrasonic imaging is mainly affected by the spatial resolution and sensitivity of the transducer [48]. Spatial resolution determines the degree of differentiation between the imaging target and other objects, and the higher the center frequency and bandwidth of the transducer are, the better the axial resolution. ...
Piezoelectric ultrasonic transducers have shown great potential in biomedical applications due to their high acoustic-to-electric conversion efficiency and large power capacity. The focusing technique enables the transducer to produce an extremely narrow beam, greatly improving the resolution and sensitivity. In this work, we summarize the fundamental properties and biological effects of the ultrasound field, aiming to establish a correlation between device design and application. Focusing techniques for piezoelectric transducers are highlighted, including material selection and fabrication methods, which determine the final performance of piezoelectric transducers. Numerous examples, from ultrasound imaging, neuromodulation, tumor ablation to ultrasonic wireless energy transfer, are summarized to highlight the great promise of biomedical applications. Finally, the challenges and opportunities of focused ultrasound transducers are presented. The aim of this review is to bridge the gap between focused ultrasound systems and biomedical applications.
... The ultrasound transducer plays a crucial role in an ultrasonic imaging system, and its center frequency directly affect ultrasonic resolution [1]. As the center frequency increases, the ultrasonic resolution increases, but the ultrasonic imaging depth decreases correspondingly [2,3]. ...
... Method (2) design two or more operating frequencies on a single transducer, so that one transducer can transmit ultrasonic waves of multiple frequencies at the same time. Transducers for method (2) are smaller in size than method (1), and multi-frequency imaging fusion has no position error, making it more beneficial to interventional ultrasound equipment [13]. Despite single transducer with multiple frequencies have advantages, they also bring challenges. ...
A micro single transducer with two resonant frequencies can solve the inherent contradiction between detection depth and resolution by simultaneously emitting two frequency bands of ultrasonic waves. But the difference of impedance values in the two resonant frequency bands seriously affects dual-frequency echo signal efficiency. In order to improve the quality of transducer sensitivity, a dual-frequency electrical impedance matching method is proposed in the study. By selecting a specific matching structure to match one frequency without messing up the
impedance of another frequency, the two frequencies can be designed independently to achieve preliminary
impedance matching. The matching networks for single frequency are combined to form a complete dualfrequency matching circuit, and adjust the initial matching value to obtain a suitable matching state. The performances of the matching network have been tested and verified by experiments. After matching, the lowfrequency and high-frequency sensitivities of the transducer increased 1.86 times and 2.26 times, respectively. In addition, system noise was also reduced by 29.6% after adding the matching network. The results demonstrate that this dual-frequency matching network can simultaneously increase the amplitude of high-frequency and low-frequency echoes to obtain better quality images.
... Phased array imaging has long been used for medical diagnosis and is widely used in various industrial fields. [22][23][24][25][26][27] This study investigates transverse-and longitudinal-wave focusing in an elastic medium by controlling the wave field propagating in a stacked thin-plate region using the characteristics of Lamb waves in thin plates, which can be theoretically predicted from the dispersion curves. ...
... Subsequently, a specific design for the stacked thin-plate region is described. Although it follows the focal law in phased-array ultrasonic focusing, [22][23][24][25][26][27] it differs in unequal thickness. As shown in Fig. 3, the thickness of the central plate in the stacked structure is d , 0 and the length is L. The center at the right edge of the stacked region is defined as the ...
This paper describes a stacked thin-plate region for focusing the transmitted waves. The region was designed to focus the wave field in the bulk medium by utilizing the dispersion nature of Lamb waves. The first numerical calculation proved that an incident plane wave changes the wavefront in a stacked thin-plate region because of the different phase velocities in plates with different thicknesses, and the resulting transmitted wave was focused at the target. Second, when a delayed longitudinal wave was applied to the edge of the stacked thin - plate region with identical thickness, the numerical calculations showed that the delayed wavefront of the S0 mode was preserved in the stacked plate region, and that the transmitted longitudinal wave was appropriately focused at the target. The focusing devise consisting of a stacked thin-plate structure is useful for the buffer for phased array inspection.
... As the core component of ultrasound devices, the ultrasonic transducer is generally composed of a piezoelectric layer, acoustic matching layer and backing layer. 6,[14][15][16] Among them, the acoustic matching layer can reduce acoustic energy reflection caused by an acoustic impedance mismatch between the piezoelectric element and human skin, [17][18][19] and can reduce the residual vibration of the transducer to reduce the tail of the ultrasonic signal. 20,21 That is, the acoustic matching layer plays an important role in improving the sensitivity and bandwidth of ultrasonic transducers. ...
Acoustic matching layers play an important role in ultrasonic transducers. However, the acoustic matching layer with both intrinsic flexibility and high acoustic impedance remains an unmet need to achieve high-performing flexible ultrasonic transducers. Herein, we present an epoxy/nano-zirconia composite with excellent flexibility and acoustic performance by the chemical coupling method. (3-Aminopropyl)triethoxysilane was used to effectively disperse nano-zirconia particles in epoxy resin, and endow the resultant composite with flexibility. After carefully adjusting the additions of nano-zirconia particles and (3-aminopropyl)triethoxysilane, the modulus of the epoxy/nano-zirconia composite was 4.5 MPa, combined with an elongation at break over 90%. The acoustic impedance of the epoxy/nano-zirconia composite (∼4.5 MRayl) exceeded that of other typical polymer counterparts. The flexible acoustic matching layer based on an epoxy/nano-zirconia composite could significantly improve the sensitivity and bandwidth of ultrasonic transducers. A fiber-shaped ultrasonic transducer with high sensitivity and wide bandwidth was fabricated, displaying promising application potential in wearable medical electronics.
... Typically, if the target entities are situated close to the skin, the transducers can be mounted on the skin. In such cases, rigid ultrasound transducers 16,47 with flat bases cannot achieve solid interfacial contact with irregular nonplanar surfaces, for instance during capturing movement of the knee while exercising. Air gaps at these interfaces lead to significant acoustic energy reflections and wave distortions, creating imaging artifacts 48 . ...
The use of bulk piezoelectric transducer arrays in medical imaging is a well-established technology that operates based on thickness mode piezoelectric vibration. Meanwhile, advancements in fabrication techniques have led to the emergence of micromachined alternatives, namely, piezoelectric micromachined ultrasound transducer (PMUT) and capacitive micromachined ultrasound transducer (CMUT). These devices operate in flexural mode using piezoelectric thin films and electrostatic forces, respectively. In addition, the development of flexible ultrasound transducers based on these principles has opened up new possibilities for biomedical applications, including biomedical imaging, sensing, and stimulation. This review provides a detailed discussion of the need for flexible micromachined ultrasound transducers (MUTs) and potential applications, their specifications, materials, fabrication, and electronics integration. Specifically, the review covers fabrication approaches and compares the performance specifications of flexible PMUTs and CMUTs, including resonance frequency, sensitivity, flexibility, and other relevant factors. Finally, the review concludes with an outlook on the challenges and opportunities associated with the realization of efficient MUTs with high performance and flexibility.
... Based on PMUTs, IVUS forms 360-degree cross-sectional images and directly assesses the morphological characteristics or properties of blood vessels by placing a micro transducer catheter into the artery [6]. Additionally, in orthopedics or ophthalmology, high-resolution images of tendons, muscles, and eyes can be obtained using high-frequency PMUT [7,8]. The measurement depth and resolution of ultrasound imaging are closely related to the frequency range of the PMUT, and high-frequency ultrasound imaging has proved to have good medical efficacy in diagnosing glaucoma and ocular tumors and assisting refractive surgery [9]. ...
Piezoelectric micromachined ultrasonic transducers (PMUTs) have attracted widespread attention due to their high performance, miniaturization, and easy integration with semiconductor processes. In this paper, a PMUT device based on high-performance and lead-free Na0.5Bi0.5TiO3-BaTiO3 (NBBT) piezoelectric single-crystal thin films was designed for the application of medical high-frequency ultrasonics. Three-dimensional modeling and analysis of PMUT elements on the proposed structure were performed via the finite element method. The relationship between structure configuration in terms of the top electrode and the cavity shape of the bottom was studied. The PMUT properties and its device performance, including resonant frequency, effective electromechanical coupling factor (keff2), and the static sensitivity of different device structures, were analyzed. In addition, by rotating the Euler Angle γ of the NBBT piezoelectric single-crystal film, the static sensitivity and keff2 of the model are improved to 1.34 when γ is rotated to 45 ± 5°. It was shown that the PMUT using rotated NBBT demonstrated an enhanced relative pulse-echo sensitivity of −46 dB and a bandwidth of 35% when the reflective surface was 200 μm. We conclude that the PMUT in accordance with an NBBT piezoelectric single-crystal film designed by simulation offers a high frequency, larger keff2, and high sensitivity, which provides application prospects in high-resolution and high-frequency medical ultrasonic imaging.
... Ultrasonography is convenient, cost-effective, no obvious harm to the examination object, dynamic observation of bilateral contrast, with very good tissue contrast and image clarity, with the continuous improvement of ultrasound instrumentation, the emission frequency continues to increase, the imaging method is gradually improved, the image is becoming clearer and clearer, showing more and more subtle structures, high-frequency ultrasound in the superficial parts of the diagnosis of soft tissue diseases play an increasingly important role in the diagnosis of. In particular, it has become an irreplaceable imaging modality for the diagnosis of breast, thyroid, superficial lymph nodes, superficial masses and other diseases [14][15][16]. High-frequency ultrasound can clearly display the muscle firmus, joint capsule, articular cartilage, and bone surface around the knee joint, and it has obvious advantages for detail display, and it can be observed dynamically in real time, and it can also be applied with new technologies such as color Doppler imaging, ultrasound elastography, and 3D imaging, which can provide the blood supply situation of the knee soft tissues, the information of the biological elasticity, and the information of the local three-dimensional reconstruction, and the high-frequency ultrasound can also well display the intra-articular cavity fluid condition, and assess the condition of exudate effusion and intra-articular free body caused by joint inflammation, trauma and other reasons [17][18][19]. ...
Knee injury is one of the common sports injuries, this paper aims to analyze the performance of ultrasound imaging technology in the assessment of early detection of athletes with knee pain, to provide a reliable assessment index for clinical diagnosis and treatment and an index for judging the efficacy. To analyze the causes of cartilage degeneration in athletes’ knee joints, and to evaluate and compare the ultrasound imaging method with the commonly used clinical assessment (Visual Analogue Scale (VAS) score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score) and imaging assessment (Digital Radiography(DR), Magnetic Resonance Imaging (MRI)) for knee osteoarthritis according to the advantageous performance of ultrasound imaging technology in the examination of knee joint diseases. The correlation between ultrasound assessment and VAS score and WOMAC score, as well as DR assessment and MRI assessment were obtained, respectively. To investigate the value of ultrasonography in the evaluation of patients with osteoarthritis of the knee. The ultrasound scores of the knee were positively correlated with the VAS scores and WOMAC scores, with correlation coefficients of 0.891 and 0.902, respectively. The correlation coefficients of ultrasound ratings with DR ratings and MRI ratings were 0.876 and 0.895, respectively (both > 0.75), which were good correlations.
... This precise targeting results in effective pain relief while allowing for better postoperative mobility and faster rehabilitation compared to other anesthetic techniques. 18,19 Multiple studies collectively support the use of 0.25 % Ropivacaine in peripheral nerve blocks, emphasizing its balance of effective analgesia, reduced motor block and favourable safety profile. These studies are: -Winnie et al 49 conducted a meta-analysis to determine the optimal dose and concentration of ropivacaine (RPV) and bupivacaine (BPV) for postoperative pain relief in paediatric abdominal surgery patients. ...
Background- Popliteal Sciatic block is a peripheral nerve block of sciatic nerve at the level of Popliteal fossa. It results in anaesthesia of the lower limb below the knee, both motor and sensory anaesthesia, with the exception of the medial leg and foot, which is the territory of the Saphenous nerve, a branch of the femoral nerve. Different adjuvants have historically been utilized to extend the duration of analgesia in peripheral nerve blocks. Research examining the pain-relieving effects of dexamethasone combined with local anesthetics like bupivacaine has yielded encouraging findings. Nonetheless, there is limited research comparing the effectiveness of dexamethasone with ropivacaine. Aims- To compare the efficacy of Dexamethasone as an adjuvant to Ropivacaine and Ropivacaine alone in ultrasound guided popliteal sciatic block. Materials and methods- this RCT done in department of anaesthesiology at NKP Salve institute of medical sciences and research centre and Lata Mangeshkar Hospital, Nagpur, Maharashtra, during the period of November 2022 to May 2024 after the approval of the Institutional Ethics Committee. Ropivacaine with and without the inclusion of Dexamethasone as an adjuvant for use in Sonography directed PSNB (Popliteal Sciatic Nerve Block) during below knee operations. As per the sample size calculated, there were 25 patients included in each group, i.e., 50 patients were taken for the study. Data was added and analysed in statistical software STATA (Version 10.1, 2011). Results- The age of participant in Cluster RD and Cluster R was 42.56 ± 14.18 years and 44.08 ± 17.17 years respectively. Male were 80% and female were 20% in group RD. Male were 72% and female were 28% in group R. ASA grade I patients were 40% and ASA grade II were 60% in group RD. ASA grade I patients were 24% and ASA grade II were 76% in group R. Mean height, mean weight and mean BMI showed statistically non-significant results. Pulse rate, systolic blood pressure and diastolic blood pressure at 1 hr, 3 hr, 6 hr, 12 hr and 24 hr are likely to be same notably between two study Clusters (P-value>0.05 for all). Respiratory Rate, Spo2, showed statistically non-significant results at each time interval 1 hr, 3 hr, 6 hr, 12 hr and 24 hr. Mean pain score at 1 hr and 6 hr did not differ significantly between two study groups (P-value>0.05). Distribution of mean pain score at 3 hr, 12 hr and 24 hr is significantly higher in Group R compared to Group RD (P-value < 0.05). Mean time for first rescue analgesia is significantly higher in Group RD compared to Group RA (P-value<0.05). Allocation of median total rescue analgesia required in 24-hrs is notably higher in group R compared to group RD and to be considered significant (P value = 0.001). Incidence of post-op complications in terms of nausea and vomiting among the cases studied are likely to be same notably among both the research. Conclusion- Ultrasound guided popliteal sciatic nerve block is efficacious and found to be higher in providing postoperative analgesia for below knee Surgeries. Addition of Dexamethasone as an adjuvant to Ropivacaine reduces pain scores, prolonged the duration of first rescue analgesia and required less postoperative analgesia compared to Ropivacaine alone. Hence based on this study, addition of Dexamethasone to Ropivacaine is highly recommended for post-operative analgesia in ultrasound guided block for below knee surgeries.
... However, optimally titrating these therapies remains a challenge due to the lack of real-time and automatic monitoring of spinal cord parameters such as hematoma development and tissue inflammation. Ultrasound is a promising diagnostic tool for SCI management, providing clinicians with real-time, remote, and portable imaging capabilities for visualizing anatomical boundaries and identifying pathological abnormalities within the tissue 11 . Brightness-mode (B-mode) ultrasound emits acoustic waves at frequencies ≥ 20 kHz to construct a two-dimensional grayscale image representing the anatomy within the imaging plane 12 . ...
While deep learning has catalyzed breakthroughs across numerous domains, its broader adoption in clinical settings is inhibited by the costly and time-intensive nature of data acquisition and annotation. To further facilitate medical machine learning, we present an ultrasound dataset of 10,223 Brightness-mode (B-mode) images consisting of sagittal slices of porcine spinal cords (N=25) before and after a contusion injury. We additionally benchmark the performance metrics of several state-of-the-art object detection algorithms to localize the site of injury and semantic segmentation models to label the anatomy for comparison and creation of task-specific architectures. Finally, we evaluate the zero-shot generalization capabilities of the segmentation models on human ultrasound spinal cord images to determine whether training on our porcine dataset is sufficient for accurately interpreting human data. Our results show that the YOLOv8 detection model outperforms all evaluated models for injury localization, achieving a mean Average Precision (mAP50-95) score of 0.606. Segmentation metrics indicate that the DeepLabv3 segmentation model achieves the highest accuracy on unseen porcine anatomy, with a Mean Dice score of 0.587, while SAMed achieves the highest Mean Dice score generalizing to human anatomy (0.445). To the best of our knowledge, this is the largest annotated dataset of spinal cord ultrasound images made publicly available to researchers and medical professionals, as well as the first public report of object detection and segmentation architectures to assess anatomical markers in the spinal cord for methodology development and clinical applications.
... Bian et al. reviewed the material-selection and fabrication processes used to make ultra-wideband ultrasonic transducers and evaluated their frequency response and bandwidth characteristics [36]. Lee et al. explored innovative transducer configurations, thereby enhancing the sensitivity and resolution of ultrasonic imaging, leading to potential advances in medical diagnostics and non-destructive testing [37,38]. Odabaee et al. used advanced modeling and simulation techniques to understand and predict the behavior of ultrasonic transducers, which led to the design and optimization of transducer systems [39]. ...
Photoacoustic imaging (PAI) is an emerging hybrid imaging modality that combines high-contrast optical imaging with high-spatial-resolution ultrasound imaging. PAI can provide a high spatial resolution and significant imaging depth by utilizing the distinctive spectroscopic characteristics of tissue, which gives it a wide variety of applications in biomedicine and preclinical research. In addition, it is non-ionizing and non-invasive, and photoacoustic (PA) signals are generated by a short-pulse laser under thermal expansion. In this study, we describe the basic principles of PAI, recent advances in research in human and animal tissues, and future perspectives.
... Due to its versatile and non-invasive properties, ultrasound imaging techniques can provide real-time, quantitative physical and anatomical information, and further facilitate to capture of meticulous information on objects in certain applications such as structural cracks, pathological tissues, and obstacles. Due to the penetration capability, safety (non-radiation), and economic efficiency properties of ultrasound, the development of ultrasound imaging benefits other ultrasound domains, especially for the ultrasonic testing (UT) technology employed in a wide variety of applications from nondestructive testing [1], [2], medical diagnosis [3], [4] to communication navigation [5], [6]. ...
This paper proposes a new 3D spatial sensing approach via compressed sensing (CS) by using a single-channel air-coupled piezoelectric micromachined ultrasonic transducer (PMUT) operated with multi-frequency. Our study focuses on a single-channel transducer with a PMUT array composed of several diaphragms with different radius sizes. It is known that small variations in the radius size can cause distinct transmission signals of all diaphragms that are excited by the same excitation signal. In this way, the acoustic field distribution of a region of interest (ROI) can be distorted especially in the direction perpendicular to the wave propagation, which could help to obtain more distinctive information about the scatterers at different locations in any 3D ROI. Therefore, a compressed 3D spatial sensing approach is proposed and used for acquiring measurements of the designed single-channel transducer. The information of any object in a 3D ROI can be mapped onto a collection of basis functions constructed via the nearly mutual orthogonal echo signals from all scatterers in the ROI. Furthermore, the proposed approach is verified with simulated acoustic measurements obtained from the established PMUT equivalent circuit model and the K-Wave acoustic propagation model via an obstacle-sensing application. Based on the sparsity nature of objects in the ROI, the reconstruction of 2D/3D images of objects can be accomplished via a CS-based algorithm. The obtained image reconstruction results show that the proposed approach allows not only for detecting localization but also for reconstructing descriptive features of an object.
... Finally, an optical heterodyne interference technique is employed to capture the signal output. Photoacoustic sensing has relied predominantly on focused piezoelectric ultrasonic transducers, with inherent limitations in size, sensitivity, and field of view 15,16 . The proposed probe utilizes an optical sensor to convert acoustic displacement into a phase delay or intensity variation of the laser beam, improving the sensitivity by two orders of magnitude. ...
A miniaturized photoacoustic fiberscope has been developed, featuring a lateral resolution of 9 microns and a lightweight design at 4.5 grams. Engineered to capture hemodynamic processes at single-blood-vessel resolution at a rate of 0.2 Hz, this device represents an advancement in head-mounted tools for exploring intricate brain activities in mobile animals.
... In essence, a CMUT is a parallel plate capacitor, with a flexible top plate (membrane) and a fixed bottom plate (substrate) ( Figure 3B) (59). CMUTs function by applying an AC voltage and a DC bias voltage simultaneously between the membrane and the substrate, which causes the membrane to move due to Coulomb forces, known as electrostatic actuation (64). The movement, as well as the vibration from the AC voltage excitation, generates ultrasonic waves (65). ...
Tissue elasticity remains an essential biomarker of health and is indicative of irregularities such as tumors or infection. The timely detection of such abnormalities is crucial for the prevention of disease progression and complications that arise from late-stage illnesses. However, at both the bedside and the operating table, there is a distinct lack of tactile feedback for deep-seated tissue. As surgical techniques advance toward remote or minimally invasive options to reduce infection risk and hasten healing time, surgeons lose the ability to manually palpate tissue. Furthermore, palpation of deep structures results in decreased accuracy, with the additional barrier of needing years of experience for adequate confidence of diagnoses. This review delves into the current modalities used to fulfill the clinical need of quantifying physical touch. It covers research efforts involving tactile sensing for remote or minimally invasive surgeries, as well as the potential of ultrasound elastography to further this field with non-invasive real-time imaging of the organ’s biomechanical properties. Elastography monitors tissue response to acoustic or mechanical energy and reconstructs an image representative of the elastic profile in the region of interest. This intuitive visualization of tissue elasticity surpasses the tactile information provided by sensors currently used to augment or supplement manual palpation. Focusing on common ultrasound elastography modalities, we evaluate various sensing mechanisms used for measuring tactile information and describe their emerging use in clinical settings where palpation is insufficient or restricted. With the ongoing advancements in ultrasound technology, particularly the emergence of micromachined ultrasound transducers, these devices hold great potential in facilitating early detection of tissue abnormalities and providing an objective measure of patient health.
... Crystals align themselves in the presence of electric current, causes the particles to change dimensions. Because of this phenomenon, it is called the piezoelectric effect [49,50]. ...
T HE Color Doppler ultrasonography is widely utilized in equines, dairy cattle, and small ruminants as a safe, non-invasive means of monitoring reproductive performance. Non-intrusive color Doppler ultrasonography was utilized to evaluate high-risk pregnancies and the health of the fetus. The alterations that take place in farm animals after giving birth are thought to be crucial in predicting future fertility. B mode ultrasonography has been applied in several studies on postpartum buffaloes. Color Doppler ultrasonography is a non-invasive technique that can be used before, during, and after delivery. Using the uterine and umbilical arteries, it is possible to evaluate the perfusion of the uteroplacental and fetoplacental blood flow in buffaloes. The motion of the transmitter and receiver affects the frequency of an ultrasonic pulse, which is a phenomenon called the Doppler Effect, and was initially described by Christian Doppler. Nowadays, the use of color Doppler ultrasonography has followed the same pattern as that of cows and other animals. Doppler ultrasound application's basis is likened to cows. The blood supply to the uterus is remarkably similar. Recent research have described the features of vaginal blood circulation in buffaloes throughout gestation and the early puerperium in addition to the uterine blood flow. The impact of vaginal blood circulation on buffalo fertility needs to be studied in the future. We highlight the different benefits of non-invasive color Doppler ultrasound applications in the buffalo's reproduction.
... Piezoelectric transducers are the most widely used ultrasound sensors in production and clinical [5] applications. The incident acoustic pressure waves deform the piezoelectric material and are measured in terms of the electric potential difference across the piezoelectric material induced by the deformation. ...
Nowadays, ultrasound sensors are playing an irreplaceable role in the fields of biomedical imaging and industrial nondestructive inspection. Currently, piezoelectric transducers are the most widely used ultrasound sensors, but their sensitivities drop quickly when the size becomes smaller, leading to a typical sensor size at the millimeter to centimeter scale. In order to realize both high sensitivity and spatial resolution, various optical ultrasound sensors have been developed. Among them, ultrasound sensors using high-Q optical microcavities have realized unprecedented sensitivities and broad bandwidth and can be mass-produced on a silicon chip. In this review, we introduce ultrasound sensors using three types of optical microcavities, including Fabry-Perot cavities, -phase-shifted Bragg gratings, and whispering gallery mode microcavities. We introduce the sensing mechanisms using optical microcavities and discuss several key parameters for ultrasound sensors. We then review the recent work on ultrasound sensing using these three types of microcavities and their applications in practical detection scenarios, such as photoacoustic imaging, ranging, and particle detection.
... COVIDx-US is an openaccess benchmark dataset of lung ultrasound imaging data that contains 242 videos and 29,651 processed images of patients with COVID-19 infection, non-COVID-19 infection (mainly pneumonia), other lung conditions, and normal control cases. The dataset provides LUS images captured with two kinds of probes, linear probes, which produce a square or rectangular image, and convex probes, which allow for a wider field of view [28]. Due to the difference in the field of view, combining the linear and convex probe data in training may increase noise and influence the performance of the network. ...
As the Coronavirus Disease 2019 (COVID-19) continues to impact many aspects of life and the global healthcare systems, the adoption of rapid and effective screening methods to prevent the further spread of the virus and lessen the burden on healthcare providers is a necessity. As a cheap and widely accessible medical image modality, point-of-care ultrasound (POCUS) imaging allows radiologists to identify symptoms and assess severity through visual inspection of the chest ultrasound images. Combined with the recent advancements in computer science, applications of deep learning techniques in medical image analysis have shown promising results, demonstrating that artificial intelligence-based solutions can accelerate the diagnosis of COVID-19 and lower the burden on healthcare professionals. However, the lack of large, well annotated datasets poses a challenge in developing effective deep neural networks, especially in the case of rare diseases and new pandemics. To address this issue, we present COVID-Net USPro, an explainable few-shot deep prototypical network that is designed to detect COVID-19 cases from very few ultrasound images. Through intensive quantitative and qualitative assessments, the network not only demonstrates high performance in identifying COVID-19 positive cases, using an explainability component, but it is also shown that the network makes decisions based on the actual representative patterns of the disease. Specifically, COVID-Net USPro achieves 99.55% overall accuracy, 99.93% recall, and 99.83% precision for COVID-19-positive cases when trained with only five shots. In addition to the quantitative performance assessment, our contributing clinician with extensive experience in POCUS interpretation verified the analytic pipeline and results, ensuring that the network’s decisions are based on clinically relevant image patterns integral to COVID-19 diagnosis. We believe that network explainability and clinical validation are integral components for the successful adoption of deep learning in the medical field. As part of the COVID-Net initiative, and to promote reproducibility and foster further innovation, the network is open-sourced and available to the public.
... Crystals align themselves in the presence of electric current, causes the particles to change dimensions. Because of this phenomenon, it is called the piezoelectric effect [49,50]. ...
The aim of the current study was to determine the changes in uterine blood flow as well as uterine biometry during the first 5 weeks after parturition in Egyptian buffaloes. The number of the experimental buffaloes used in the present thesis was 35.
In the first group (n=5) of the experiment, transrectal noninvasive color Doppler ultrasound was measured at different time points [-5, -4, -3, -2, -1, 0 (day of parturition), 1, 2, 3, 4, 5]. BFV, PSV, TAMV, PI, RI, S/D as well as diameter of uterine and vaginal arteries were the Doppler indices for the determination of uterine and vaginal blood flow changes. BFV of uterine artery was significantly higher in the days -5, -4, -3 and -2 (P<0.0001). The maximum increase was in the last day of pregnancy.
A steep decrease after parturition from day 1 to 5 (P<0.0001). RI and PI of the uterine artery of the gravid uterine horns increased steadily from day of parturition until day 5 postpartum in the Egyptian buffaloes (P<0.001).
RI and PI of vaginal artery values decrease during the last 5 days of gestation and then increase after the day of parturition. The lowest values were on the 3rd day after parturition (P<0.05). Also we used the changes of the plasma steroids in uterine and vaginal blood flow dynamics as reference values for normal puerperium in the Egyptian buffaloes.
In the second group (n=30) of the experiment, transrectal color Doppler indices was measured at different time points [-7, 0 (day of parturition), 7, 14, 21, 28, 35] after postpartum periods. BFV, PSV, TAMV, PI, RI, S/D as well as the diameter of uterine arteries were the Doppler indices for determination of uterine artery blood flow changes during different time points after parturition. BFV of uterine arteries decreased linearly during the postpartum period in Egyptian buffaloes. The BFV decreased from 3029.21 ml/min (-7 day) to 343.84 ml/min
(35 day pp) and moderately (P < 0.01) to 731 ml/min on (day 28).
The TAMV and PSV showed fluctuation in changes during different time points postpartum (P < 0.05). But PI, RI, and S/D showed significant increases during the different time points postpartum (P < 0.01). The mean diameter of the uterine horn decreased significantly from day 0 to day 35 after parturition (P < 0.0001). The uterine involution was completed on day 28, as demonstrated by transrectal palpation and B-mode sonography. The mean diameter of the dominant follicle at day 7 postpartum in Egyptian buffaloes was 5.4 ± 0.4 mm and by days 28 and 35 we investigated a significant change in the dominant follicle diameter, which was 12.9 ± 0.6 and 14.06 ± 0.56 mm respectively. Altogether, the results show that transrectal color Doppler ultrasound is a successful tool for examining uterine changes during the first 5 weeks after parturition in Egyptian buffaloes. The robust changes in uterine blood flow were demonstrated during the first week of the puerperium, The PI, RI, and S/D were also suitable to investigate alterations in uterine perfusion during the next 5 weeks after parturition.
... COVIDx-US is an open-access benchmark dataset of lung ultrasound imaging data that contains 242 videos and 29,651 processed images of patients with COVID-19 infection, non-COVID-19 infection, other lung conditions, and normal control cases. The dataset provides LUS images captured with two kinds of probe, linear probe which produces a square or rectangular image, or convex probe, which allows for a wider field of view [28]. Due to the difference in field of view and low numbers of COVID-19 positive examples with linear probe, combining the linear and convex probe data in training may increase noise and influence the performance of the network and hence, linear probe data are excluded in this study. ...
As the Coronavirus Disease 2019 (COVID-19) continues to impact many aspects of life and the global healthcare systems, the adoption of rapid and effective screening methods to prevent further spread of the virus and lessen the burden on healthcare providers is a necessity. As a cheap and widely accessible medical image modality, point-of-care ultrasound (POCUS) imaging allows radiologists to identify symptoms and assess severity through visual inspection of the chest ultrasound images. Combined with the recent advancements in computer science, applications of deep learning techniques in medical image analysis have shown promising results, demonstrating that artificial intelligence-based solutions can accelerate the diagnosis of COVID-19 and lower the burden on healthcare professionals. However, the lack of a huge amount of well-annotated data poses a challenge in building effective deep neural networks in the case of novel diseases and pandemics. Motivated by this, we present COVID-Net USPro, an explainable few-shot deep prototypical network, that monitors and detects COVID-19 positive cases with high precision and recall from minimal ultrasound images. COVID-Net USPro achieves 99.65% overall accuracy, 99.7% recall and 99.67% precision for COVID-19 positive cases when trained with only 5 shots. The analytic pipeline and results were verified by our contributing clinician with extensive experience in POCUS interpretation, ensuring that the network makes decisions based on actual patterns.
... The abdomen is scanned in four areas (or views) -subxiphoid, right hypochondrium, left hypochondrium, and suprapubic (Figure 3). Both pleural cavities just above the diaphragm and pleural Ultrasound probes -Linear (a) and curvilinear (b) [4]. ...
Abdominal trauma is difficult to identify, especially in a patient with multiple injuries. Mechanism of injury can guide us to the likely organs injured, but the extent and location cannot be accurately pinpointed in most cases. Owing to the multitude of structures located in the abdomen, timely identification and appropriate intervention are crucial to ensure the good patient outcomes. Focused assessment with sonography in trauma (FAST) and its extended version (eFAST) has become the standard care as per ATLS guidelines in patient evaluation. The main goal is to identify hemoperitoneum, hemothorax, and/or pneumothorax. However, sonography can be applied to detect varying injuries to abdominal viscera, beyond the elementary eFAST examination. This includes assessment of solid organs, hollow viscus, vascular structures, and even soft tissues. Sonography, when wielded with necessary knowledge and practice, can be an incredible asset at the bedside. This chapter aims to explore these possible applications of point of care ultrasonography (POCUS) in abdominal trauma.
In this study, we have developed an optical fiber ultrasound emitter based on the thermal cavitation effect. A tube filled with a highly absorptive liquid is sealed at the end of an optical fiber pigtail. A continuous-wave laser is transmitted through the fiber, heating the highly absorptive copper salt solution near the fiber end face to its spinodal limit. Using a single-mode fiber, we achieved ultrasound pulses with an amplitude of 330 kPa and a repetition rate of 4 kHz in the frequency range of 5–17 MHz, and a bandwidth of 12 MHz was obtained by using a low laser heating power of 52 mW at a wavelength of 974 nm. This optical fiber ultrasound emitter features a simple fabrication process, low cost, and low optical power consumption. Its flexible design allows for easy integration into medical devices with small dimensions and makes it suitable for non-destructive testing in confined spaces.
Mapping wave field in space has many applications such as optimizing design of radio antennas, improving and developing ultrasound transducers, and planning and monitoring the treatment of tumors using high-intensity focused ultrasound (HIFU). Currently, there are methods that can map wave fields remotely or locally. However, there are limitations with these methods. For example, when mapping the wave fields remotely, the spatial resolution is limited due to a poor diffractionlimited resolution of the receiver, especially when the f -number of the receiver is large. To map the wave fields locally, the receiver is either subject to damage in hazardous environments (corrosive media, high temperature, and high wave intensity, etc) or difficult to be placed inside an object. To address these limitations, in this paper, the PSF-modulation super-resolution imaging method (January, 2024 IEEE TUFFC) was applied to map pulse ultrasound wave fields remotely at a high spatial resolution, overcoming the diffraction limit of a focused receiver. For example, to map a pulse ultrasound field of a full-width-at-half-maximum (FWHM) beam width of 1.24 mm at the focal distance of a transmitter, the FWHM beam widths of the super-resolution mapping of the pulse wave field with a spherical glass modulator of 0.7-mm diameter at two receiver angles (0° and 45°) were about 1.13 mm and 1.22 mm respectively, which were close to the theoretical value of 1.24 mm and were much smaller than the diffraction-limited resolution (1.81 mm) of the receiver. Without using the super-resolution method to remotely map the same pulse wave field, the FWHM beam width was about 2.06 mm. For comparison, the FWHM beam width obtained with a broadband (1-20 MHz) and 0.6-mm diameter polyvinylidene fluoride (PVDF) needle hydrophone was about 1.41 mm. In addition to the focused pulse ultrasound wave field, a pulse Bessel beam near the transducer surface was mapped remotely with the super-resolution method, which revealed high spatial frequency components of the beam.
The study on the effective radii of ultrasonic transducers for hydrophone calibration at the National State Primary Standard of the Unit of Ultrasonic Pressure in Water (NDETU AUV-02-2018) is presented and the appropriate method is described. The impact of the effective radius on measurement distance and diffraction loss coefficients is evaluated. The uncertainty calculation of the effective radius measurement of ultrasonic transducers is provided, and its influence on the accuracy of hydrophone calibration is assessed. Considerable attention is given to estimating the measurement distance between the hydrophone and the ultrasonic transducer, which significantly affects the accuracy of hydrophone calibration.
Ultrasound sensors play an important role in biomedical imaging, industrial nondestructive inspection, etc. Traditional ultrasound sensors that use piezoelectric transducers face limitations in sensitivity and spatial resolution when miniaturized, with typical sizes at the millimeter to centimeter scale. To overcome these challenges, optical ultrasound sensors have emerged as a promising alternative, offering both high sensitivity and spatial resolution. In particular, ultrasound sensors utilizing high-quality factor ( Q ) optical microcavities have achieved unprecedented performance in terms of sensitivity and bandwidth, while also enabling mass production on silicon chips. In this review, we focus on recent advances in ultrasound sensing applications using three types of optical microcavities: Fabry-Perot cavities, π-phase-shifted Bragg gratings, and whispering gallery mode microcavities. We provide an overview of the ultrasound sensing mechanisms employed by these microcavities and discuss the key parameters for optimizing ultrasound sensors. Furthermore, we survey recent advances in ultrasound sensing using these microcavity-based approaches, highlighting their applications in diverse detection scenarios, such as photoacoustic imaging, ranging, and particle detection. The goal of this review is to provide a comprehensive understanding of the latest advances in ultrasound sensing with optical microcavities and their potential for future development in high-performance ultrasound imaging and sensing technologies.
In this paper, the design, fabrication and comparison of Pb(Mg
1/3
Nb
2/3
)O
3
-0.25PbTiO
3
(PMN-0.25PT) single crystals (SCs) by alternating current poling (ACP) and direct current poling (DCP)-based 2.8 MHz phased array ultrasonic transducers were investigated. Pzflex finite element simulation was utilized to model and compare the electro-acoustic properties of ACP and DCP phased arrays. The finite element analysis (FEA) results indicated that the ACP phased arrays can exhibit a greater sensitivity, a broader -6dB@bandwidth, and a lower center frequency under the same acoustic structure and the same thickness of matching layers. In addition, the high coincidence of simulated and measured impedance proves the stability of the transducer fabrication processes. By comparing the permittivity of the SCs in the processes of transducer fabrication, it is shown that the ACP SCs are more sensitive to the clamping force during the pressurization process and to the cutting force during the dicing process, respectively. Compared with the DCP phased arrays, the ACP phased arrays have been shown to exhibit 7.90% increase in observed -6dB@bandwidth and 0.82 dB increase in relative sensitivity. These results suggest that ACP phased arrays can enhance both the longitudinal resolution and penetration depth of ultrasonic imaging. Finally, a typical phantom image is created to compare the imaging capabilities of ACP and DCP phased arrays. The findings indicate that phased arrays based on ACP PMNT SCs might be promising for medical ultrasound imaging applications.
The objective of this work was to investigate changes in the acoustic characteristics of micromachined transducers caused by acoustic cross-coupling between cells. We used hexagonal, polymer-based capacitive micromachined ultrasonic transducers (polyCMUTs) consisting of 127 cells connected in parallel. The distances between the cells were varied, while the cell dimensions and number of cells remained constant. The resulting changes in characteristics were evaluated in terms of peak frequency
fpk
, fractional bandwidth
FBW
, peak transmit sensitivity
Spk
and opening angle Φ
t
. The study relies on results from an analytic multicell model (MCM) which considers cross-coupling effects between cells through a mutual acoustic impedance matrix. The results are compared with finite element (FE) analyses and measurements on fabricated prototypes. The manufacturing processes used to produce the polyCMUT prototypes are explained in detail. We found significant changes in all acoustic characteristics: as cell spacing increases,
fpk
and Φ
t
decrease, while
Spk
gradually rises to about twice the initial value. The
FBW
varies due to the change in
fpk
, peaking at small to intermediate cell-to-cell distances. While both modeling approaches cover the general effects, discrepancies in comparison to the measurements were identified. The FE model provided better fits than the analytic MCM, albeit at significantly higher computational costs. The effects on the acoustic characteristics were found strongest at lower frequencies and if many cells are in close proximity to each other. Hence, rotational symmetric or square transducers operating at lower frequencies are affected most. The results demonstrate that design approaches based on modeling single cells may lead to significant deviations from design goals. Both, analytic and FE models are suitable tools to estimate the effects of acoustic interactions and to predict the performance. This aids in meeting design requirements of micromachined ultrasound transducers consisting of multiple radiators.
Two-dimensional ultrasound transducers enable the acquisition of fully volumetric data that have been demonstrated to provide greater diagnostic information in the clinical setting and are a critical tool for emerging ultrasound methods, such as super-resolution and functional imaging. This technology, however, is not without its limitations. Due to increased fabrication complexity, some matrix probes with disjoint piezoelectric panels may require initial calibration. In this manuscript, two methods for calibrating the element positions of the Vermon 1024-channel 8 MHz matrix transducer are detailed. This calibration is a necessary step for acquiring high resolution B-mode images while minimizing transducer-based image degradation. This calibration is also necessary for eliminating vessel-doubling artifacts in super-resolution images and increasing the overall signal-to-noise ratio (SNR) of the image. Here, we show that the shape of the point spread function (PSF) can be significantly improved and PSF-doubling artifacts can be reduced by up to 10 dB via this simple calibration procedure.
Implanted bio-electronic (IBE) devices such as pacemakers and neurostimulators have become increasingly important for therapeutic and diagnostic medical purposes. The life span of the IBE batteries ranges from several months...
The sensitive membrane of capacitive ultrasonic transducers is quite crucial for their performances, which can affect sensitivity, bandwidth, acoustic impedance, etc. In this study, an air-coupled capacitive ultrasonic transducer array is proposed with sensitive materials of MXenes. The air-coupled ultrasonic array with a Ti3C2Tx diaphragm is designed and fabricated. The array is
in size, with a membrane radius of 1 mm and a central frequency of 112.5 kHz. The simulation and experiments of the array are carried out to analyze the effect of the transducer characteristics by direct current (dc) bias voltages and alternating current (ac) excitation. The transmitting and receiving performance of the designed array are tested, and the results demonstrate that the array has outstanding sound pressure level (SPL) and receiving sensitivity. The feasibility of using Ti3C2Tx as a capacitive ultrasonic transducer diaphragm is indicated in this article, which expands the potential applications in acoustic measurement, detection, and imaging.
This work demonstrates the imaging capabilities of a silicon-on-nothing (SON) ScAlN piezoelectric micromachined ultrasonic transducer (pMUT) array by a method of transmit beamforming followed by suitable signal postprocessing for 3-D image reconstruction. A 2.7-MHz pMUT array with 15% scandium-doped aluminum nitride (ScAlN) as the piezo thin film was implemented for this demonstration. A total of
-mm dies consisting of
pMUT elements per die and operated as dual channels were arranged in an eight-column
two-row array configuration, resulting in a 32-channel experimental system with a
-mm coverage. In this work, experimental testing using single and multiple 6-mm-diameter reflectors at a different spacing from each other and a distance of 2.5 cm from the array was performed to validate the 3-D imaging capabilities of the developed 2-D SON ScAlN pMUT array with an attained lateral resolution of 5 mm.
The fabrication of a fully printed, lead‐free, polymer piezoelectric transducer is presented and the characterization of its structural, dielectric, and ferroelectric properties at different processing stages is demonstrated. The performance of poly(vinylidene fluoride‐trifluoroethylene) transducers with resonance frequency analyses, acoustic power measurements, and pulse‐echo experiments is evaluated. Notably, for the first time for a fully printed transducer, an optimal performance in the medical ultrasound range (<15 MHz) is demonstrated with acoustic power >1 W cm⁻², which is promising for applications in epidermal and wearable electronics. Overall, the findings provide a strong foundation for future research in the area of flexible ultrasound transducers.
Ultrasound transducer is a crucial component for several imaging modalities, where acoustic sensing is utilized as a part of hybrid or combination of pure optical and ultrasound imaging. However, conventional ultrasound transducers are opaque, and the optical components in the system require a different pathway to avoid any interference. The absence of coaxial integration limits the optical illumination area, adds complexity, and makes the system bulky. Moreover, the system performance is deteriorated due to the unoptimized illumination in hybrid imaging and the lack of correlation between the data acquired through the combined modalities. To overcome these drawbacks, different approaches to realize optically transparent ultrasound transducers have been explored that includes piezoelectric-based and microelectromechanical system-based capacitive and piezoelectric ultrasonic transducers. Unlike conventional opaque transducers, each component of transparent ultrasound transducers requires specific materials and a certain recipe which all together determine the overall performance of the transducer. In this article, we have performed a comparative analysis on the materials and the fabrication process used to make different types of transparent ultrasound transducer.
This paper is an exhaustive survey of computer-aided diagnosis (CAD) system-based automatic detection of several diseases from ultrasound images. CAD plays a vital role in the automatic and early detection of diseases. Health monitoring, medical database management, and picture archiving systems became very feasible with CAD, assisting radiologists in making decisions over any imaging modality. Imaging modalities mainly rely on machine learning and deep learning algorithms for early and accurate disease detection. CAD approaches are described in this paper in terms of it's their significant tools; digital image processing (DIP), machine learning (ML), and deep learning (DL). Ultrasonography (USG) already has many advantages over other imaging modalities; therefore, CAD analysis of USG assists radiologists in studying it more clearly, leading to USG application over various body parts. This paper includes a review of those major diseases whose detection supports “ML algorithm” based diagnosis from USG images. ML algorithm follows feature extraction, selection, and classification in the required class. The literature survey of these diseases is grouped into the carotid region, transabdominal & pelvic region, musculoskeletal region, and thyroid region. These regions also differ in the types of transducers employed for scanning. Based on the literature survey, we have concluded that texture-based extracted features passed to support vector machine (SVM) classifier results in good classification accuracy. However, the emerging deep learning-based disease classification trend signifies more preciseness and automation for feature extraction and classification. Still, classification accuracy depends on the number of images used for training the model. This motivated us to highlight some of the significant shortcomings of automated disease diagnosis techniques. Research challenges in CAD-based automatic diagnosis system design and limitations in imaging through USG modality are mentioned as separate topics in this paper, indicating future scope and improvement in this field. The success rate of machine learning approaches in USG-based automatic disease detection motivated this review paper to describe different parameters behind machine learning and deep learning algorithms towards improving USG diagnostic performance.
OBJETIVOS: Descrever a técnica ultrassonográfica utilizada para verificar o posicionamento do tubo em trato gastrointestinal e verificar se ultrassonografia é um método confiável para confirmar o posicionamento do tubo enteral. MÉTODO: Trata-se de uma revisão integrativa de literatura. A busca foi realizada no mês de maio de 2022 na Biblioteca Virtual em Saúde. Os critérios de inclusão foram: artigos publicados entre os anos de 2017 a 2022, cuja população estudada fosse acima de 18 anos, independente do idioma e país que foi realizado. RESULTADOS: Foram selecionados 17 estudos, todos eles descreveram a técnica utilizada, sendo possível identificar os principais pontos de convergência. Quanto à confiança do método para visualização do tubo enteral, o valor preditivo positivo variou de 91 a 100%, já o valor preditivo negativo teve uma variação grande de 11,1% a 100%. CONCLUSÃO: Essa revisão aponta para muitas convergências quanto às técnicas de insonação para avaliação da localização do tubo enteral, sendo assim um ponto de partida para os profissionais que pretendem avançar no uso desta ferramenta. Os estudos também indicam que o ultrassom é uma ferramenta promissora para a confirmação do posicionamento do tubo enteral. No entanto, a taxa de sucesso de visualização do tubo enteral no trato gastrointestinal, assim como o valor preditivo positivo ainda são muito variáveis, além das limitações mencionadas para o seu uso. Assim, se faz necessário mais pesquisas, a fim de construir protocolos seguros de uso do ultrassom como tecnologia confiável de confirmação do tubo de alimentação enteral.
Introduction:
Previous studies have shown that ultrasonography has high specificity (80%-100%) but low sensitivity (50%-70%) in diagnosing fatty liver; sensitivity is especially low for mild steatosis. In this study, we aimed to reappraise the diagnostic performance of B-mode ultrasonography (B-USG) for fatty liver disease.
Methods:
We performed a retrospective, multinational, multicenter, cross-sectional, observational study (6 referral centers from 3 nations). We included 5,056 participants who underwent both B-USG and magnetic resonance proton density fat fraction (MRI-PDFF) within a 6-month period. The diagnostic performance of B-USG was compared with that of MRI-PDFF as a reference standard for fatty liver diagnosis, using sensitivity, specificity, positive and negative predictive values, diagnostic accuracy, and area under the receiver operating characteristic curve (AUC).
Results:
B-USG showed a sensitivity of 83.4%, specificity of 81.0%, and AUC of 0.822 in diagnosing mild liver steatosis (6.5% ≤MRI-PDFF ≤14%). The sensitivity, specificity, and AUC in diagnosing the presence of fatty liver disease (MRI-PDFF ≥6.5%) were 83.4%, 81.0%, and 0.822, respectively. The mean PDFF of B-USG-diagnosed nonfatty liver differed significantly from that of diagnosed mild liver steatosis (3.5% ± 2.8% vs 8.5% ± 5.0%, P < 0.001). The interinstitutional variability of B-USG in diagnosing fatty liver was similar in diagnostic accuracy among the 6 centers (range, 82.8%-88.6%, P = 0.416).
Discussion:
B-USG was an effective, objective method to detect mild liver steatosis using MRI-PDFF as comparison, regardless of the etiologies and comorbidities.
New designs of high-resolution ultrasonic imaging systems that operate in the 30–100 MHz region, for example, those based on linear transducer systems, are currently being investigated for medical purposes. Acoustic waves with frequencies in this range can detect microscopic structures in human tissue but will typically only penetrate a few mm because of large attenuation. However, this is sufficient for a diagnostic ultrasound scan of human skin. The signal-to-noise ratio and the focusing properties of the scanner are critical factors in dermatology, which are determined by the transducer design. A linear pulsed PVDF transducer array with a center frequency around 45 MHz is studied by applying numerical simulations, based on the finite element method (FEM), of this electromechanical system. Tx-beamforming properties of linear arrays with one, three, five, and seven active elements are investigated at different depths. The image quality obtained from synthetic Rx-beamforming, using responses from five electrodes, is estimated from reconstructed images of 25–100 μm thick objects. The axial and lateral resolutions of these images are found to be similar with the Tx-beamforming resolution parameters estimated from the time-derivative of the pressure beams.
Over the past two decades, intravascular ultrasound (IVUS) image segmentation has remained a challenge for researchers while the use of this imaging modality is rapidly growing in catheterization procedures and in research studies. IVUS provides cross-sectional grayscale images of the arterial wall and the extent of atherosclerotic plaques with high spatial resolution in real time. In this paper, we review recently developed image processing methods for the detection of media-adventitia and luminal borders in IVUS images acquired with different transducers operating at frequencies ranging from 20 to 45 MHz. We discuss methodological challenges, lack of diversity in reported datasets, and weaknesses of quantification metrics that make IVUS segmentation still an open problem despite all efforts. In conclusion, we call for a common reference database, validation metrics, and ground-truth definition with which new and existing algorithms could be benchmarked.
We present simulation and experimental results from a 5-MHz, 256 x 256 2-D (65,536 elements, 38.4 x 38.4 mm) 2-D array transducer with row-column addressing. The main benefits of this design are a reduced number of interconnects, a modified transmit/receive switching scheme with a simple diode circuit, and an ability to perform volumetric imaging of targets near the transducer with transmit beamforming in azimuth and receive beamforming in elevation. The final dimensions of the transducer were 38.4 mm x 38.4 mm x 300 microm. After a row-column transducer was prototyped, the series resonance impedance was 104 Omega at 5.4 MHz. The measured -6 dB fractional bandwidth was 53% with a center frequency of 5.3 MHz. The SNR at the transmit focus was measured to be 30 dB. At 5 MHz, the average nearest neighbor crosstalk was -25 dB. In this paper, we present 3-D images of both 5 pairs of nylon wires embedded in a clear gelatin phantom and an 8 mm diameter cylindrical anechoic cyst phantom acquired from a 256 x 256 2-D array transducer made from a 1-3 composite. We display the azimuth and elevation B-scans as well as the C-scan for each image. The cross-section of the wires is visible in the azimuth B-scan, and the long axes can be seen in the elevation B-scan and C-scans. The pair of wires with 1-mm axial separation is discernible in the elevational B-scan. When a single wire from the wire target phantom was used, the measured lateral beamwidth was 0.68 mm and 0.70 mm at 30 mm depth in transmit beamforming and receive beamforming, respectively, compared with the simulated beamwidth of 0.55 mm. The cross-section of the cyst is visible in the azimuth B-scan whereas the long axes can be seen as a rectangle in the elevation B-scan and C-scans.
Plate waves inside the piezoelectric layer are much involved in the elements cross-coupling in transducer arrays for medical imaging. In this work, such waves are analyzed in 1-3 piezocomposite materials on the basis of conventional guided modes formalism in which the piezocomposite is considered as a homogeneous medium. Cross-coupling measurements have been made on two different transducer arrays using network analyzer and a laser interferometric probe. It is shown how the analysis in terms of symmetrical Lamb waves gives an interesting qualitative interpretation, explaining most of the cross-coupling amplitude variations with frequency. Results show that the 0th and 3rd symmetrical Lamb waves are mainly involved in coupling inside composite plates. The S0 mode is responsible for the inter-element coupling, whereas the S3 mode widens the effective width of the excited element.
Transesophageal echocardiography (TEE) is an essential diagnostic tool in patients with poor transthoracic echocardiographic windows or when detailed imaging of structures distant from the chest wall is necessary. A real-time 3D TEE probe has been fabricated in our laboratory in order to increase the amount of information available during a transesophageal procedure. The 1 cm diameter esophageal probe utilizes a 2-dimensional, 5 MHz array at its tip with a 6.3 mm diameter aperture, including 504 active channels. The array has a periodic vernier geometry with an element pitch of 0.18 mm, built onto a multilayer flexible (MLF) interconnect circuit. In order to accommodate 504 channels within the device, a 1 m long Gore MicroFlat cable was utilized for wiring the MLF to the corresponding system connectors. Pulse-echo tests in a water tank have yielded a -6 dB bandwidth of 25.3%. Fully connected to the system through 3 m of cable, the probe shows an average 50 omega insertion loss of-85 dB with a standard deviation of 4 dB, as determined through pitch-catch measurements for a sampling of 10 elements. Using the completed 3D TEE probe with the Volumetrics Medical Imaging 3D scanner, real-time volumetric images of in vivo canine cardiac anatomy have been acquired, displaying atrial views, mitral valve function and interventional catheter guidance.
2-D array transducers present a major interest for ultrasound volumetric imaging as they allow data acquisition and visualization in real time. However their manufacture remains a technological challenge because of the very high number of elements with reduced lateral dimensions close to a half wavelength pitch. During this work, we developed and set up an industrial process to manufacture fully connected array through an innovative rear material, combining the backing function and the high density interconnect. This process does not affect the acoustical behavior of each elements and the connection of all elements is performed in a single operation. In addition, for the acoustical design, specific backing and matching layers structure have been implemented to reduce cross-talk and to increase the acceptance angle. A 2D fully populated array, based on this design, with a 3 MHz center frequency, 300 microns pitch, containing, 4096 elements (64×64) is presented. The evaluation of the performances over the array includes electroacoustical characterizations (pulse echo waveforms and spectrum), electrical measurements (electrical impedance and cross-talk) and acceptance angle data, obtained by hydrophone setup techniques. This design can be applied to many configurations, over a wide range of pitch and frequency, from fully populated to sparse array.
Piezoelectric materials have dominated the ultrasonic transducer technology. Recently, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as an alternative technology offering advantages such as wide bandwidth, ease of fabricating large arrays, and potential for integration with electronics. The aim of this paper is to demonstrate the viability of CMUTs for ultrasound imaging. We present the first pulse-echo phased array B-scan sector images using a 128-element, one-dimensional (1-D) linear CMUT array. We fabricated 64- and 128-element 1-D CMUT arrays with 100% yield and uniform element response across the arrays. These arrays have been operated in immersion with no failure or degradation in performance over the time. For imaging experiments, we built a resolution test phantom roughly mimicking the attenuation properties of soft tissue. We used a PC-based experimental system, including custom-designed electronic circuits to acquire the complete set of 128/spl times/128 RF A-scans from all transmit-receive element combinations. We obtained the pulse-echo frequency response by analyzing the echo signals from wire targets. These echo signals presented an 80% fractional bandwidth around 3 MHz, including the effect of attenuation in the propagating medium. We reconstructed the B-scan images with a sector angle of 90 degrees and an image depth of 210 mm through offline processing by using RF beamforming and synthetic phased array approaches. The measured 6-dB lateral and axial resolutions at 135 mm depth were 0.0144 radians and 0.3 mm, respectively. The electronic noise floor of the image was more than 50 dB below the maximum mainlobe magnitude. We also performed preliminary investigations on the effects of crosstalk among array elements on the image quality. In the near field, some artifacts were observable extending out from the array to a depth of 2 cm. A tail also was observed in the point spread function (PSF) in the axial direction, indicating the -
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existence of crosstalk. The relative amplitude of this tail with respect to the mainlobe was less than -20 dB.
Present 1D phased array probes have outstanding lateral and axial resolution, but their elevation performance is determined by a fixed aperture focused at a fixed range. Multi-row array transducers can provide significantly improved elevation performance in return for "modest" increases in probe and system complexity. Time domain simulations of elevation beam profiles are used to compare several types of multi-row probes. The elevation aperture of a 1.25D probe increases with range, but the elevation focusing of that aperture is static and determined principally by a mechanical lens with a fixed focus (or foci). 1.25D probes can provide substantially better near- and far-field slice thickness performance than 1D probes and require no additional system beamformer channels. 1.5D, probes use additional beamformer channels to provide dynamic focusing and apodization in elevation. 1.5D probes can provide detail resolution comparable to, and contrast resolution substantially better than, 1.25D probes, particularly in the mid- and far-field. Further increases in system channel count allow the use of 1.75D and 2D arrays for adaptive acoustics and two-dimensional beam steering. Significant improvements in clinical image quality can be expected as multi-row probes become increasingly available in the marketplace.
When the driving voltage of an ultrasonic transducer is increased to improve the quality of ultrasound images, heat is generated inside the transducer, which can burn the patient's skin and degrade transducer performance. In this study, the method to disperse the heat inside an ultrasonic phased-array transducer has been examined. The mechanism of temperature rise due to heat generation inside the transducer was investigated by numerical analysis and the effects of the thermal properties of the components of the transducer such as specific heat and thermal conductivity on the temperature rise were analyzed. On the basis of the results, a heat-dispersive structure was devised to reduce the temperature at the surface of the acoustic lens of the transducer. Prototype transducers were fabricated to check the efficacy of the heat-dispersive structure. By experiments, we have confirmed that the new heat-dispersive structure can reduce the internal temperature by as much as 50% in comparison with the conventional structure, which confirms the validity of the thermal dispersion mechanism developed in this work.
A piezoelectric micromachined ultrasonic transducer (pMUT) has enabled numerous exciting ultrasonic applications. However, residual stress and initial buckling may worsen the transmitting sensitivity of a pMUT, and also limit its application and commercialization. In this paper, we report a new innovative pMUT with a perfectly flat membrane, i.e., zero-bending membrane. Leveraging on the stress-free AlN thin film, framelike top electrode layout, and integrated vacuum cavity, the initial deflection of suspended membrane is significantly suppressed to only 0.005%. The transmitting sensitivity of the zero-bending pMUT is measured as 123 nm/V at a resonant frequency of 2.21 MHz, which is 450% higher than that of the reference pMUT with slightly non-zero initial deflection. Compared with the simulation results, the measured data of zero-bending pMUT achieve 94.5% of its ideal transmitting sensitivity. It is solid evidence that our approach is an effective and reliable way to overcome the residual stress and the initial buckling issue. [2015-0093]
The increasing use of Point of Care (POC) ultrasound presents a challenge in providing efficient training to POC ultrasound users for whom formal training is not readily available. In response to this need, we developed an affordable, compact, laptop-based obstetric ultrasound training simulator. It offers a realistic scanning experience, task-based training and performance assessment. The position and orientation of the sham transducer are tracked with 5 degrees of freedom on an abdomen-sized scan surface with the shape of a cylindrical segment. On the simulator user interface is rendered a virtual torso, whose body surface models the abdomen of the pregnant scan subject. A virtual transducer scans the virtual torso, by following the sham transducer movements on the scan surface. A given 3D training image volume is generated by combining several overlapping 3D ultrasound sweeps acquired from the pregnant scan subject using a Markov random field based approach. Obstetric ultrasound training is completed through a series of tasks, guided by the simulator and focused on three aspects: basic medical ultrasound, orientation to obstetric space, and fetal biometry. The scanning performance is automatically evaluated by comparing user-identified anatomical landmarks with reference landmarks pre-inserted by sonographers. The simulator renders 2D ultrasound images in real-time with 30 fps or higher with good image quality; the training procedure follows standard obstetric ultrasound protocol. Thus, for learners without access to formal sonography programs, the simulator is intended to provide structured training in basic obstetrics ultrasound.
Backings for ultrasonic transducers are generally made of composites of metal or metal oxide powder and epoxy resin or rubber. In this work, a new highly attenuative backing has been developed by installing cylindrical silicone rubber rods periodically inside the two phase mixture. The scattering of ultrasonic waves is dramatically increased by the polymeric rods, which results in big improvement of the attenuation. The silicone rubber rods are molded first, and are disposed periodically on a plane. Then a mixture of epoxy and metallic powder is casted around the rods, and is cured not to have any vacancies. Another backing plate was fabricated as well with the same mixture but without the silicone rods. The backing plates were characterized through ultrasonic pulse-echo tests. Significant improvement of the attenuation has been confirmed through the experiments. Acoustic impedance of the backing can be increased if needed by controlling the volume percent of tungsten powder without causing much variation of the attenuation. This highly attenuative backing is applicable to various size-constrained ultrasound probes like TEE and mechanical 3D transducers.
Three-dimensional (3D) ultrasound imaging allows physicians to use ultrasound to view pathology as a volume in order to enhance the comprehension of a patient's anatomy. In this paper, the modality of 3D ultrasound imaging is described in accordance with the development of transducer technology. Two representative types of 3D imaging transducers are reviewed with description of the concept and operation principle of each type: mechanical transducer and matrix array transducer. Mechanical transducers are further divided into free-hand scanning and sequential scanning types. Matrix array transducers are also detailed into piezoelectric (single-unit and module-assembly type) transducers and capacitive micromachined ultrasound transducers. Advantages of each transducer and technical issues for further performance enhancement are discussed.
Matrix array transducers have been developed in this work for cardiac imaging in real-time and 3D. The matrix array transducers have 4,096 (64×64) active elements made of the piezoelectric single crystals, PMN-PT, within 1 inch square. Two different matrix array structures have been developed: (1) fabrication of whole 64×64 elements as a single unit on a PMN-PT plate with a conductive backing, and (2) assembly of eight 64×8 element modules to compose 64×64 channels. Optimal structures of the two matrix array transducer types have been determined through finite element analysis to have their center frequency at 3.5 MHz and fractional frequency bandwidth over 60%. In the single unit structure, it was very difficult to achieve good enough uniformity over the whole 4,096 elements, which was likely to cause serious difficulty in production of the transducer. The acoustic module assembly technique was developed to resolve the problem. In case some elements showed big deviation in performance due to mistakes in fabrication, that particular module containing the bad elements could be easily replaced with a good one. However, the module assembly method necessitated more complicated fabrication processes. Fabricated prototypes of the transducers satisfied the design specifications very well.
Capacitive micromachined ultrasonic transducers (CMUTs) manufactured on silicon substrates need an acoustic backing to suppress substrate ringing when such transducers are in operation. The acoustic backing most often used for ultrasound transducers is a composite of epoxy and tungsten powder. To absorb the acoustic energy, the backing of a CMUT should have an acoustic impedance that matches that of the silicon substrate and it should be lossy. If the backing is thick enough, it will absorb the acoustic wave in the backing without reflecting it back to the transducer, and thus will not create any trailing echoes. However, if we intend to use the transducer in applications in which there is no room for a thick backing, for example in intravascular ultrasound (IVUS), a grooved backing structure might be used. The grooves at the bottom of the backing provide extra attenuation by scattering the waves in different directions so that a thinner backing is sufficient. The scattering removes power from the specular reflection from the back surface which otherwise degrades the image quality. It has been shown that this type of structure reduces the specular reflection for a range of frequencies. When CMUTs are used in practical applications, the propagation of waves from a fluid medium into the backing or vice versa is blocked to some degree by total reflection, except for a range of steering angles around broadside. This is due to the difference in acoustic velocities of silicon and the fluid medium. This blocking is accompanied by the generation of surface waves in the silicon substrate, which also may impact the imaging and therefore must be controlled. In this paper, we investigate the acoustic signal transmitted into the backing relative to the signal transmitted into the fluid medium when CMUT arrays on top of the silicon substrate are excited. Furthermore, the performance of the grooved backing structure is studied for the waves traveling in normal as well as in obliqu
This third edition provides a concise and generously illustrated survey of the complete field of medical imaging and image computing, explaining the mathematical and physical principles and giving the reader a clear understanding of how images are obtained and interpreted. Medical imaging and image computing are rapidly evolving fields, and this edition has been updated with the latest developments in the field, as well as new images and animations. An introductory chapter on digital image processing is followed by chapters on the imaging modalities: radiography, CT, MRI, nuclear medicine and ultrasound. Each chapter covers the basic physics and interaction with tissue, the image reconstruction process, image quality aspects, modern equipment, clinical applications, and biological effects and safety issues. Subsequent chapters review image computing and visualization for diagnosis and treatment. Engineers, physicists and clinicians at all levels will find this new edition an invaluable aid in understanding the principles of imaging and their clinical applications.
The basics of ultrasonic transducer array design in the frequency range useful for medical imaging are discussed. Performance parameters of importance in transducer design are considered, including sensitivity, coupling constant, band width, frequency downshift, pulse duration, beam focusing properties, and electrical matching. 2D and 3D effects must also be taken into account. The advantages of computer modeling in 3D with finite element analysis code are highlighted. The principles of multi-element array transducers useful for 2D real-time scanning are reviewed. 2D arrays provide the opportunity of focusing the elevation beam dimension in the short axis, or make possible full D scanning volumes.
The transducer under consideration is a planar two-dimensional (2D) array transducer working at 3.5 MHz. The transducer is composed of 17× 17 piezoelectric elements separated by major and minor kerfs. Through finite element analyses (FEA), the performance of the 2D array transducer was investigated in relation to the acoustic impedance and structure of the kerfs. Based on the analysis results, three new types of kerfs were proposed to reduce the cross-talk. Detailed material properties and structures of the new kerfs were determined to provide the lowest cross-talk level and highest pulse-echo sensitivity while preserving a desired acceptance angle at the center frequency of 3.5 MHz. The results in this work can contribute to developing a 2D array transducer which would result in having a higher signal-to-noise level, which in turn will lead to better ultrasonic imaging.
The classic acoustics reference! This widely-used book offers a clear
treatment of the fundamental principles underlying the generation,
transmission, and reception of acoustic waves and their application to
numerous fields. The authors analyze the various types of vibration of
solid bodies and the propagation of sound waves through fluid media.
A 1.5-D transducer array was proposed to improve acoustic radiation force impulse (ARFI) imaging signal-to-noise ratio (SNRARFI) and image contrast relative to a conventional 1-D array. To predict performance gains from the proposed 1.5-D transducer array, an analytical model for SNRARFI upper bound was derived. The analytical model and 1.5-D ARFI array were validated using a finite element modelbased numerical simulation framework. The analytical model demonstrated good agreement with numerical results (correlation coefficient = 0.995), and simulated lesion images yielded a significant (2.92 dB; p < 0.001) improvement in contrast-tonoise ratio when rendered using the 1.5-D ARFI array.
Transesophageal echocardiography (TEE) is established as an essential diagnostic tool for patients that are obese or that exhibit signs of pulmonary disease. A real-time 3D TEE probe has been fabricated in our laboratory in order to improve on the shortcomings of current TEE devices and increase the amount of information available during a transesophageal procedure. The 8 mm diameter endoscope probe utilizes a 2D, 5 MHz array at its tip with a 6.3 mm diameter aperture, including 504 active channels. The array has a periodic vernier geometry with an element pitch of 0.18 mm, and it was built on a multilayer flexible interconnect circuit (MLF). In order to accommodate 504 channels within the endoscope, 1 m long Gore MicroFlat™ cable was utilized for wiring the MLF to the corresponding system connectors. Using the completed 3D TEE probe with a volumetrics medical imaging 3D scanner, real-time volumetric images of in vivo canine cardiac anatomy have been acquired, displaying atrial views, mitral valve function, and catheter guidance.
Effects of heavy density (p = 9.2 x 103 kg/m3) Yb2O3 fine dopant (16 nm in diameter) on the acoustic properties of a high-temperature-vulcanization (HTV) silicone rubber have been investigated, to develop a new acoustic lens material with a low acoustic attenuation (alpha) for the medical array probe application. The HTV silicone rubber has advantages in that it shows a lower alpha than that of a room-temperature-vulcanization (RTV) silicone rubber and it can be mixed by applying shear stress, using roll-milling equipment. Roll-milling time dependence of the HTV silicone rubber indicates that the alpha is closely affected by the dispersion of nanopowders in the rubber matrix. The 8 vol% Yb2O3-doped HTV silicone rubber mixed for 30 min showed the lowest alpha of 0.73 dB/mmMHz with an acoustic impedance [AI = sound speed (c) times density (p)] of 1.43 times 106 kg/m2s at 37degC. Moreover, simulation results reveal that a 5 MHz linear probe using the HTV silicone rubber doped with Yb2O3 powder showed relative sensitivity around 2.6 to 3.0 dB higher than a probe using RTV silicone rubber doped with Yb2O3 powder or SiO2-doped conventional silicone rubber for the ultrasonic medical application.
An ultrasound probe for three-dimensional scanning and focusing of an ultrasound beam in both an azimuth direction and an elevation direction normal to the azimuth direction. The probe is composed of an ultrasound transducer array which has a linear division of the elements in the azimuth direction for electronic steering of the beam direction and focus in the azimuth direction. The array elements have a coarse division in the elevation direction for electronic steering of the focus in the elevation direction, and possibly small angle direction steering of the beam in the elevation direction for parallel receive and/or transmit beams. Large angle direction scanning of the beam in the elevation direction is obtained by mechanical rotation of the array around an axis. The invention implies useful embodiments for insertion of the probe into the body, through mounting the array at the distal tip of an elongated device.
State-of-the-art 3-D medical ultrasound imaging requires transmitting and receiving ultrasound using a 2-D array of ultrasound transducers with hundreds or thousands of elements. A tight combination of the transducer array with integrated circuitry eliminates bulky cables connecting the elements of the transducer array to a separate system of electronics. Furthermore, preamplifiers located close to the array can lead to improved receive sensitivity. A combined IC and transducer array can lead to a portable, high-performance, and inexpensive 3-D ultrasound imaging system. This paper presents an IC flip-chip bonded to a 16 x 16-element capacitive micromachined ultrasonic transducer (CMUT) array for 3-D ultrasound imaging. The IC includes a transmit beamformer that generates 25-V unipolar pulses with programmable focusing delays to 224 of the 256 transducer elements. One-shot circuits allow adjustment of the pulse widths for different ultrasound transducer center frequencies. For receiving reflected ultrasound signals, the IC uses the 32-elements along the array diagonals. The IC provides each receiving element with a low-noise 25-MHz-bandwidth transimpedance amplifier. Using a field-programmable gate array (FPGA) clocked at 100 MHz to operate the IC, the IC generated properly timed transmit pulses with 5-ns accuracy. With the IC flip-chip bonded to a CMUT array, we show that the IC can produce steered and focused ultrasound beams. We present 2-D and 3-D images of a wire phantom and 2-D orthogonal cross-sectional images (Bscans) of a latex heart phantom.
Multilayer ultrasonic transducers are widely being used for high power applications. In these applications, typical Langevin/Tonpilz structures without any adhesive bondings however have the disadvantage of limited bandwidth. Therefore adhesively-bonded structures are still a potential solution for this issue. In this paper, two-layer piezoelectric ceramic ultrasonic transducers with two different adhesive bondlines were investigated comparing to a single-layer transducer in terms of loss effects during operation with excitation signals sufficient to cause self-heating. The theoretical functions fitted to the measured time-temperature dependency data are compared with experimental results of different piezoelectric transducers. Theoretical analysis of loss characteristics at various surface displacements and the relationship with increasing temperature are reported. The effects of self-heating on the practical performance of multilayer ultrasonic transducers with adhesive bondlines are discussed.
To study perforation rates of sterile transvaginal ultrasound probe covers before and after oocyte retrieval (OPU) in an IVF-ET program.
Transvaginal ultrasound probe sheaths from two different manufacturers were studied, Cook Innoray (Cook-Canada #TTUPS-100) and Swemed Lab (Frolunda Sweden #715). After controlled ovarian stimulation, OPU was done using the needle guide of a sterile sheathed 5-MHz transvaginal ultrasound transducer (ATL Bothell, Washington, USA). A newer designed Cook probe cover supplied by the manufacturer was also tested after the company was made aware of our initial perforation results. Following each OPU, probe covers were examined for perforations by filling them with water and checking for leaks. If perforations were found, the vaginal transducer was disinfected by soaking for 20 min in 2% gluteraldehyde (Formac). Twenty unused sterile probe covers from each manufacturer were also tested for perforations.
After OPU we found 10/13 (75%) old Cook, and 35/43 (81%) Swemed probe covers to be perforated (NS). Only 5/20 (25%) of the new design Cook probe covers were perforated post OPU (p = 0.000005). Analysis of unused probe covers revealed 13/20 (65%) Cook, and 5/20 (25%) Swemed probe covers to be perforated (P = 0.02). None of 10 new design unused Cook probe covers were perforated before use.
A simple electro-mechanical equivalent circuit model is used to predict the behavior of capacitive micromachined ultrasonic transducers (cMUT). Most often, cMUTs are made in silicon and glass plates that are in the 0.5 mm to 1 mm range in thickness. The equivalent circuit model of the cMUT lacks important features such as coupling to the substrate and the ability to predict cross-talk between elements of an array of transducers. To overcome these deficiencies, a flnite element model of the cMUT is constructed using the commercial code ANSYS. Calculation results of the complex load impedance seen by single capacitor cells are presented, then followed by a calculation of the plane wave real load impedance seen by a parallel combination of many cells that are used to make a transducer. Cross-talk between 1-D array elements is found to be due to two main sources: coupling through a Stoneley wave propagating at the transducer-water interface and coupling through Lamb waves propagating in the substrate. To reduce the cross-talk level, the effect of structural variations of the substrate are investigated, which includes a change of its thickness and etched trenches or polymer walls between array elements.
Although the advantages of three-dimensional (3-D) echocardiography have been acknowledged, its application for routine diagnosis is still very limited. This is mainly due to the relatively long acquisition time. Only recently has this problem been addressed with the introduction of new real-time 3-D echo systems. This paper describes the design, characteristics, and capabilities of an alternative concept for rapid 3-D echocardiographic recordings. The presented fast-rotating ultrasound (FRU)-transducer is based on a 64-element phased array that rotates with a maximum speed of 8 Hz (480 rpm). The large bandwidth of the FRU-transducer makes it highly suitable for tissue and contrast harmonic imaging. The transducer presents itself as a conventional phased-array transducer; therefore, it is easily implemented on existing 2-D echo systems, without additional interfacing. The capabilities of the FRU-transducer are illustrated with in-vitro volume measurements, harmonic imaging in combination with a contrast agent, and a preliminary clinical study.
The effects of fine metal oxide particles, particularly those of high-density elements (7.7 to 9.7 x 10(3) kg/m3), on the acoustic properties of silicone rubber have been investigated in order to develop an acoustic lens with a low acoustic attenuation. Silicone rubber doped with Yb2O3 powder having nanoparticle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with powders of CeO2, Bi2O3, Lu2O3 and HfO2. The silicone rubber doped with Yb2O3 powder showed a sound speed of 0.88 km/s, an acoustic impedance of 1.35 x 10(6) kg/m2s, an acoustic attenuation of 0.93 dB/mmMHz, and a Shore A hardness of 55 at 37 degrees C. Although typical silicone rubber doped with SiO2 (2.6 x 10(3) kg/m3) shows a sound speed of about 1.00 km/s, heavy metal oxide particles decreased the sound velocities to lower than 0.93 km/s. Therefore, an acoustic lens of silicone rubber doped with Yb2O3 powder provides increased sensitivity because it realizes a thinner acoustic lens than is conventionally used due to its low sound speed. Moreover, it has an advantage in that a focus point is not changed when the acoustic lens is pressed to a human body due to its reasonable hardness.
The major advantages of single crystals (PMN-PT and PZN-PT) over conventional PZT 5H are their high piezoelectric and electro-mechanical coupling constants, which are attractive for high performance transducers. Other properties that contribute to transducer performance, such as velocity, clamped dielectric constant and coercive field, are generally lower for single crystals than for PZT. This paper reviews the strengths and limitations of single crystals for medical ultrasound applications. It is likely impractical to use this material for devices with center frequencies higher than 6 MHz, because of the exceptional fragility, the low sound velocity and the low coercive field of single crystal material. For very low frequency arrays with small elements, electrical impedance becomes very high, which causes severe mismatch to the cable and system. An example of a 2.5MHz fine-pitch array with PMN-PT and a triple-layer PZT-5H with simulated and experimental data shows that the single layer PMN-PT array underperforms the multi-layer PZT transducer. Our experience suggests that optimal applications for single crystals in medical ultrasound applications are transducers with 3-5MHz center frequencies and preferably large elements. The results for a 300 μm pitch, 3MHz PMN-PT array with 90% fractional bandwidth compared to 75% for the same PZT array are presented.
A design method for acoustic thin disk transducers with high efficiency, broad bandwidth, and good impulse response is presented. This method is based on the use of quarter-wave matching layers between the piezoelectric material and the acoustic load. As is made evident using the transmission line model of Krimholtz, Leedom, and Matthaei, the finite thickness of the piezoelectric material must be taken into account in the matching layer design. Criteria for optimum broad-band transducer designs with a given piezoelectric material are developed which show the importance of a high electromechanical coupling coefficient. A method for obtaining Gaussian shaped passbands, necessary for optimum impulse response, is also shown. Several transducers have been built to illustrate this design approach with excellent agreement between theory and experiment. One such transducer has 3.2 dB round trip insertion loss and one octave bandwidth.
The effects of fine metal oxide particles, particularly those of high-density elements (7.7 to 9.7 times 103 kg/m3), on the acoustic properties of silicone rubber have been investigated in order to develop an acoustic lens with a low acoustic attenuation. Silicone rubber doped with Yb2O3 powder having nanoparticle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with powders of CeO2, Bi2O3, Lu2O3 and HfO2. The silicone rubber doped with Yb2O3 powder showed a sound speed of 0.88 km/s, an acoustic impedance of 1.35 times 106 kg/m2s, an acoustic attenuation of 0.93 dB/mmMHz, and a Shore A hardness of 55 at 37degC. Although typical silicone rubber doped with SiO2 (2.6 times 103 kg/m3) shows a sound speed of about 1.00 km/s, heavy metal oxide particles decreased the sound velocities to lower than 0.93 km/s. Therefore, an acoustic lens of silicone rubber doped with Yb2O3 powder provides increased sensitivity because it realizes a thinner acoustic lens than is conventionally used due to its low sound speed. Moreover, it has an advantage in that a focus point is not changed when the acoustic lens is pressed to a human body due to its reasonable hardness.
Finite element (PZFlex; Weidlinger Assoc., New York, NY and Los Altos, CA) simulations predict that for a 2-MHz phased array element with a single matching layer, the three-layer hybrid structure increases the pulse echo signal-to-noise ratio (SNR) by 16 dB over that from a single layer PZT element and -6 dB pulse echo fractional bandwidth from 58% for the PZT element to 75% for the hybrid element. Analogous finite element method (FEM) simulations of single crystal material [lead zinc niobate (PZN)-8% lead titanate (PT)] showed increased SNR by only 3.1 dB, but a -6 dB bandwidth of 108%.
For medical ultrasound imaging, 2-D array transducers have greater versatility than linear arrays. Unfortunately, the tiny array elements in a 2-D array have poor signal-to-noise ratio (SNR). We have previously shown that SNR is increased in 2-D array transducers made from piezoelectric multilayer ceramics. Conventional one-dimensional models provide accurate results when comparing multilayer ceramic performance relative to single layer transducers. However, these models are not accurate when comparing simulations directly to measurements. Because multilayer ceramics have a complex structure, a 3-D model, such as finite element analysis, is needed for accurate simulations. We modeled four arrays that were previously fabricated: a single layer and multilayer 1 MHz, 2-D array element, and a single layer and multilayer 2.25 MHz, 1.5-D array element that can focus and steer in azimuth but only steer in the elevation dimension. We compared the simulated and measured impedance plots for each transducer. The finite element analysis plots accurately predicted the impedance for each vibration mode. On the other hand, the one dimensional KLM transmission line model could simulate only the thickness mode vibrations and the results were inaccurate compared to measurements. We also simulated the transmit output pressure for the 2.25 MHz arrays and compared the results to measurements. The simulated pressure vs. time plots and their spectra were accurate when compared to measurements. Finally, we obtained a series of images that show the impulse response vibrations for the 2.25 MHz, arrays. These animations show the vibration modes in the complex multilayer ceramic structure. Measurements were not available to confirm the animations. Our results show that finite element analysis in three dimensions is a valuable tool to predict the performance of multi-layer transducers.
Ultrasound trasnducer with improved rigid backing
- Sliwa
- Jw
- S Ayter
- C G Sridhar
- J P Mohr
- S M Howard
- M H Ikeda
Single crystals versus PZT ceramics for medical ultrasound applications In: Conference proceedings of the IEEE ultrasonic symposium
- Xm Lu
- Tl Proulx
Ultrasound transducer
- C R Mequio
Wideband acoustic transducer
- P G Barthe
- M H Slayton