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Fabrication and Characterization of Tissue-Mimicking Phantoms for Ultrasound-Guided Cannulation Training
Abstract
Tissue-mimicking materials (TMMs) have been investigated and used for decades as imaging phantoms in various medical applications. They are designed and fabricated to replicate certain biological tissue characteristics, a process often dictated by the target application. Moreover, TMMs have been utilized in some medical procedural training requiring the use of imaging modalities. One potential application for TMMs is ultrasound-guided cannulation training. Cannulation is a procedure that requires a level of dexterity to gain vascular access using ultrasound guidance while avoiding complications like vessel laceration and bleeding. However, an ideal phantom for this application is yet to be developed. This work investigates the development and characterization of high-fidelity phantoms for cannulation training. The mechanical (shore hardness, elastic modulus, and needle-interaction forces) and acoustic (B-mode ultrasound scans) properties of candidate materials were quantitatively compared with biological tissue. The evaluated materials included ballistic gel, plasticized polyvinyl chloride (PVC), silicone, gelatin, agar, and polyvinyl alcohol (PVA)- cryogel. Mechanical testing demonstrated that each material could replicate the Shore hardness and elasticity characteristics of different biological tissues (skin, fat, and muscle), with PVA and PVC showing tunability by varying composition or fabrication processes. Shore hardness (OO-range) for PVA ranged between 6.3 ± 1.0 to 59.3 ± 2.6 and PVC from 4.8 ± 0.7 to 14.6 ± 0.8. Ultrasound scans of PVA were the closest to human scans, both qualitatively (based on experts' opinion) and quantitatively (based on pixel intensity measurements). Modified mixtures of PVA are found to best serve as high-fidelity cannulation phantoms. Alternatively, PVC can be used to avoid troublesome fabrication processes of PVA.
... Phantoms were constructed based on eight guiding principles for a robust test rig [25], including tissue-like properties and tunability of the gelatin stiffness, stability of the properties over time, architectural exibility to be adjusted to suit the desired vein characteristics, reproducibility of the gelatin fabrication, simple maintenance, nontoxic, and having ingredients that are readily available. Phantoms were created using a mixture of gelatin powder, water, vinegar, and Metamucil, as outlined in Appendix B. The gelatin hydrogel provides a tissue-mimicking bulk material with similar mechanical behaviour to native human tissue [26][27][28]. Metamucil increases echogenicity of the gelatin phantom to show acoustic similarity to human tissue under ultrasound [27,29,30]. White vinegar was added to preserve the longevity of the gelatin phantoms [31]. ...
... Phantoms were created using a mixture of gelatin powder, water, vinegar, and Metamucil, as outlined in Appendix B. The gelatin hydrogel provides a tissue-mimicking bulk material with similar mechanical behaviour to native human tissue [26][27][28]. Metamucil increases echogenicity of the gelatin phantom to show acoustic similarity to human tissue under ultrasound [27,29,30]. White vinegar was added to preserve the longevity of the gelatin phantoms [31]. ...
Inserting needles into veins is fundamental to medical care with up to 90% of inpatients requiring a peripheral intravenous catheter/cannula (PIVC) during their stay. Yet 40%-50% of PIVC insertions fail on the first attempt. Here, we present an easy-to-use novel vein visualizing ultrasound prototype device and data from in vitro and in vivo performance. Our prototype’s locational accuracy in simulated forearm veins is 0.16mm ±1.63mm (s.d.) (97.8% agreement to the ground truth, p<.001), across variations of vein diameter (3-5mm), depth (10-20mm), and velocity (10-100mm/s). Usability trials conducted with nine clinicians found that 100% of users were able to handle the prototype in a sterile manner with minimal assistance. In 80 forearm scans of 40 volunteers, sensitivity was excellent to both find veins (94%). In comparison, sensitivity of vein finding using landmark technique with torniquet (visible 46% and palpable 74%) were far inferior. The prototype is a novel ultrasound device which empowers clinicians to detect and visualize well-perfused veins at depth in the coronal view of vein pathways whilst enabling, ultra portability, accessibility and ease of use.
... The surrounding tissue was formulated by combing equal amounts of Part A and Part B of Gel-00 (Polytek Development Corp., Easton, PA, USA). Gel-00, softer than Gel-10, was selected to achieve tissues with a Shore hardness of OO 30, in line with the mechanical properties of the surrounding tissue [29]. The mixture was then placed in a Figure 1. ...
... The surrounding tissue was formulated by combing equal amounts of Part A and Part B of Gel-00 (Polytek Development Corp., Easton, PA, USA). Gel-00, softer than Gel-10, was selected to achieve tissues with a Shore hardness of OO 30, in line with the mechanical properties of the surrounding tissue [29]. The mixture was then placed in a vacuum chamber to eliminate air bubbles before being poured into 3D-printed moulds, resulting in the creation of vessel-tissue phantoms. ...
Age-related vessel deterioration leads to changes in the structure and function of the heart and blood vessels, notably stiffening of vessel walls, increasing the risk of developing cardiovascular disease (CVD), which accounts for 17.9 million global deaths annually. This study describes the fabrication of custom-made silicon vessels with varying mechanical properties (arterial stiffness). The primary objective of this study was to explore how changes in silicone formulations influenced vessel properties and their correlation with features extracted from signals obtained from photoplethysmography (PPG) reflectance sensors in an in vitro setting. Through alterations in the silicone formulations, it was found that it is possible to create elastomers exhibiting an elasticity range of 0.2 MPa to 1.22 MPa. It was observed that altering vessel elasticity significantly impacted PPG signal morphology, particularly reducing amplitude with increasing vessel stiffness (p < 0.001). A p-value of 5.176 × 10−15 and 1.831 × 10−14 was reported in the red and infrared signals, respectively. It has been concluded in this study that a femoral artery can be recreated using the silicone material, with the addition of a softener to achieve the required mechanical properties. This research lays the foundation for future studies to replicate healthy and unhealthy vascular systems. Additional pathologies can be introduced by carefully adjusting the elastomer materials or incorporating geometrical features consistent with various CVDs.
... For example, hardness can be tailored by changing the ratio of softener to PVC polymer, introducing mineral oil to lubricate the needle insertion, and including glass beads to disperse acoustic energy similar to biological tissue [22]. In addition, the acoustic properties of PVA provide US images with echogenicities closer to those from humans [25]. PVA has been used as a gelling agent for the fabrication of multimodal phantom complexes, which are similar to soft tissue, providing a unique tool for application in a variety of uses [26]. ...
... PVA has been used as a gelling agent for the fabrication of multimodal phantom complexes, which are similar to soft tissue, providing a unique tool for application in a variety of uses [26]. The disadvantage is due to its manufacturing process, which requires detailed and precise temperature control, using the freeze-thaw technique, in addition to a long post-manufacturing time [25][26][27]. ...
The objective of this paper is to review and compare the different commercial and homemade models of ultrasound-guided vascular cannulation phantoms, as well as the methods used for the elaboration of the latter. There are a variety of simulators for ultrasound-guided puncture techniques, from simple homemade phantoms to the most sophisticated and expensive virtual reality simulators. Commercial-grade ultrasound phantoms are expensive and although they are reusable, their cost can be a barrier to simulation-based training. Homemade phantoms are a cost-effective, highly useful tool for teaching vascular access using ultrasound. For the elaboration of the homemade ones, different substances and elements are usually used to produce varied echogenicities and geometries. Specifically, animal-based ones provide more realistic tissue feedback and have a back-ground echogenicity that is closer to that of human tissue. A powerful alternative is the use of poly vinyl alcohol or modified mixtures of this material, which would be better suited to cannulation simulation with high functional fidelity.
... Tissue-mimicking phantoms can be used to calibrate systems [10], assess image quality [11], train operators [12], and evaluate the effectiveness of systems [13]. Tissuemimicking phantoms also offer various benefits to researchers and clinicians, allowing them to simulate real clinical scenarios and assess the performance of elastography systems under controlled conditions [14]. ...
Breast ultrasound elastography phantoms are valued for their ability to mimic human tissue, enabling calibration for quality assurance and testing of imaging systems. Phantoms may facilitate the development and evaluation of ultrasound techniques by accurately simulating the properties of breasts. However, selecting appropriate tissue-mimicking materials for realistic and accurate ultrasound exams is crucial to ensure the ultrasound system responds similarly to real breast tissue. We conducted a systematic review of the PubMed, Scopes, Embase, and Web of Sciences databases, identifying 928 articles in the initial search, of which 19 were selected for further evaluation based on our inclusion criteria. The chosen article focused on tissue-mimicking materials in breast ultrasound elastography phantom fabrication, providing detailed information on the fabrication process, the materials used, and ultrasound and elastography validation of phantoms. The phantoms fabricated from Polyvinyl Chloride Plastisol, silicon, and paraffin were best suited for mimicking breast, fatty, glandular, and parenchyma tissues. Adding scatterers to these materials facilitates accurate fatty and glandular breast tissue simulations, making them ideal for ultrasound quality assurance and elastography training. Future research should focus on developing more realistic phantoms for advanced medical training, improving the practice of difficult procedures, enhancing breast cancer detection research, and providing tailored tissue characteristics.
... Many techniques, including experimental study, can be utilized to validate computational models. The initial stage was to prepare the phantoms, and after reviewing the relevant literature, it was determined that gelatinagar was the best material to represent human tissue [55][56][57][58] . Different groups of phantoms representing normal and cancerous tissue were created to capture the range of viscosity parameters. ...
Estimating the tissue parameters of skin tumors is crucial for diagnosis and effective therapy in dermatology and related fields. However, identifying the most sensitive biomarkers require an optimal rheological model for simulating skin behavior this remains an ongoing research endeavor. Additionally, the multi-layered structure of the skin introduces further complexity to this task. In order to surmount these challenges, an inverse problem methodology, in conjunction with signal analysis techniques, is being employed. In this study, a fractional rheological model is presented to enhance the precision of skin tissue parameter estimation from the acquired signal from torsional wave elastography technique (TWE) on skin tumor-mimicking phantoms for lab validation and the estimation of the thickness of the cancerous layer. An exhaustive analysis of the spring-pot model (SP) solved by the finite difference time domain (FDTD) is conducted. The results of experiments performed using a TWE probe designed and prototyped in the laboratory were validated against ultrafast imaging carried out by the Verasonics Research System. Twelve tissue-mimicking phantoms, which precisely simulated the characteristics of skin tissue, were prepared for our experimental setting. The experimental data from these bi-layer phantoms were measured using a TWE probe, and the parameters of the skin tissue were estimated using inverse problem-solving. The agreement between the two datasets was evaluated by comparing the experimental data obtained from the TWE technique with simulated data from the SP- FDTD model using Pearson correlation, dynamic time warping (DTW), and time-frequency representation. Our findings show that the SP-FDTD model and TWE are capable of determining the mechanical properties of both layers in a bilayer phantom, using a single signal and an inverse problem approach. The ultrafast imaging and the validation of TWE results further demonstrate the robustness and reliability of our technology for a realistic range of phantoms. This fusion of the SP-FDTD model and TWE, as well as inverse problem-solving methods has the potential to have a considerable impact on diagnoses and treatments in dermatology and related fields.
... Firstly, the number of studies reviewed was relatively small despite a large number of studies having been carried out on phantom fabrication between 2013 and 2023. This was largely due to a significant proportion of the ultrasound phantom fabrication studies failing to note the critical properties, including the speed of sound and attenuation coefficient [66][67][68]. Secondly, only one of the studies reviewed provided an SWE ultrasound image of the TMM phantom. ...
Medical imaging has allowed for significant advancements in the field of ultrasound procedures over the years. However, each imaging modality exhibits distinct limitations that differently affect their accuracy. It is imperative to ensure the quality of each modality to identify and eliminate these limitations. To achieve this, a tissue-mimicking material (TMM) phantom is utilised for validation. This study aims to perform a systematic analysis of tissue-mimicking materials used for creating ultrasound phantoms. We reviewed 234 studies on the use of TMM phantoms in ultrasound that were published from 2013 to 2023 from two research databases. Our focus was on studies that discussed TMMs’ properties and fabrication for ultrasound, elastography, and flow phantoms. The screening process led to the selection of 16 out of 234 studies to include in the analysis. The TMM ultrasound phantoms were categorised into three groups based on the solvent used; each group offers a broad range of physical properties. The water-based material most closely aligns with the properties of ultrasound. This study provides important information about the materials used for ultrasound phantoms. We also compared these materials to real human tissues and found that PVA matches most of the human tissues the best.
... In a relevant study by Jafary et al. [3], many TMMs have been tested under several aspects, including mechanical properties and B-mode visualization, J Mater Sci Industrial Engineering of the University of Florence (DIEF). ...
Purpose. High-fidelity mannequins are increasingly used to train the medical staff on many medical procedures. Lately, a new challenge regarding echogenic materials to build ultrasound-responding phantoms has emerged. The challenge is to find materials with a suitable combination of ultrasound velocity and consistency to the touch. Methods. Bibliographic research was performed to identify materials with promising stiffness, shape retention, and ultrasound velocity combinations. As-standardized-as-possible specimens were realized and tested using an A-mode ultrasound machine to evaluate the US velocity through them. Four differently doped silicones, five gelatin-based materials, five synthetic gelatins, and a 3D printable resin were included in the study. After being tested, the materials were monitored for 12 days to assess their durability and shape retention and tested again to evaluate the ultrasound velocity’s stability. In the paper, the results of the characterization and follow-up of the materials are presented. Results. Outcomes show that gelatins are exceptional soft tissue-mimicking materials in terms of ultrasound velocity and consistency to the touch, but are poor in terms of overtime stability and therefore suitable for disposable short-term phantoms only. Doped silicones present lower ultrasound velocity compared to the reference value of 1540 m/s found in the literature, but excellent overtime stability, and shape retention properties. Values close to biological ones were also given by the Elastic 50A and by polyvinyl chloride plastisol. Conclusion. The paper gives a quantitative overview of the fidelity of both already-in-use and non-conventional materials, focusing on the ultrasound velocity value through them and their longevity in terms of macroscopically observed dehydration, shape retention, and bacterial onset.
... experimental study, can be utilized to validate computational models. The initial stage was to prepare the phantoms, and after reviewing the relevant literature, it was determined that gelatin-agar was the best material to represent human tissue Chen, Balter, Chen, Gross, Alam, Maguire and Yarmush (2016) ;Li, Karmakar, Li, Kwok and Kee (2011);Pogue and Patterson (2006) ;Jafary, Armstrong, Byrne, Stephens, Pellegrino and Gregory (2022). Different groups of phantoms representing normal and cancerous tissue were created to capture the range of viscosity parameters. ...
Estimating the tissue parameters of skin tumors is crucial for diagnosis and effective therapy in dermatology and related fields. However, identifying the most sensitive biomarkers require an optimal rheological model for simulating skin behavior this remains an ongoing research endeavor. Additionally, the multi-layered structure of the skin introduces further complexity to this task. In order to surmount these challenges, an inverse problem methodology, in conjunction with signal analysis techniques, is being employed. In this study, a fractional rheological model is presented to enhance the precision of skin tissue parameter estimation from the acquired signal from torsional wave elastography technique (TWE) on skin tumor-mimicking phantoms for lab validation and the estimation of the thickness of the cancerous layer. An exhaustive analysis of the spring-pot model (SP) solved by the finite difference time domain (FDTD) is conducted. The results of experiments performed using a TWE probe designed and prototyped in the laboratory were validated against ultrafast imaging carried out by the Verasonics Research System. Twelve tissue-mimicking phantoms, which precisely simulated the characteristics of skin tissue, were prepared for our experimental setting. The experimental data from these bi-layer phantoms were measured using a TWE probe, and the parameters of the skin tissue were estimated using inverse problem-solving. The agreement between the two datasets was evaluated by comparing the experimental data obtained from the TWE technique with simulated data from the spring-pot FDTD model using Pearson correlation, dynamic time warping (DTW), and time-frequency representation. Our findings show that the spring-pot FDTD model and TWE are capable of determining the mechanical properties of both layers in a bilayer phantom, using a single signal and an inverse problem approach. The ultrafast imaging and the validation of TWE results further demonstrate the robustness and reliability of our technology for a realistic range of phantoms. This fusion of the spring-pot FDTD model and TWE, as well as inverse problem-solving methods has the potential to have a considerable impact on diagnoses and treatments in dermatology and related fields.
In this paper, we present a multi-criteria prioritization of tissue-mimicking materials for ultrasound elastography imaging experiments. A decision matrix with target-based criteria and interval data has been formed to rank the nine most suitable materials for the application based on nine target-based decision criteria. Criteria weights are calculated using the best-worst method (BWM), the entropy weight method, and the correlation of criteria weights. The existing Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method is not suitable for the multi-criteria decision making (MCDM) problems in biomedical applications where target-based criteria and uncertain data are involved. Therefore, to use the TOPSIS method for such problems, the method has been modified and named the Interval data and Target criteria based TOPSIS (IT-TOPSIS) method. This IT-TOPSIS method and an extended VlseKriterijuska Optimizacija I Komoromisno Resenje (VIKOR) method are then used to rank the materials. The study found that polyvinyl alcohol (PVA) is the best-suited soft tissue-mimicking material for ultrasound elastography imaging experiments, followed by gelatine and polyethylene glycol diacrylate (PEGDA).
Purpose Ultrasound (US) represents the primary approach for abdominal diagnosis and is regularly used to guide diagnostic and therapeutic interventions (INVUS). Due to possible serious INVUS complications, structured training concepts are required. Phantoms can facilitate teaching, but their use is currently restricted by complex manufacturing and short durability of the materials. Hence, the aim of this study was the development and evaluation of an optimized abdominal INVUS phantom.
Materials and Methods Phantom requirements were defined in a structured research process: Skin-like surface texture, homogeneous matrix with realistic tissue properties, implementation of lesions and abscess cavities in different sizes and depths as well as a modular production process allowing for customized layouts. The phantom prototypes were evaluated in certified ultrasound courses.
Results In accordance with the defined specifications, a new type of matrix was developed and cast in multiple layers including different target materials. The phantom structure is based on features of liver anatomy and includes solid focal lesions, vessels, and abscess formations. For a realistic biopsy procedure, ultrasound-proof material was additionally included to imitate bone. The evaluation was performed by US novices (n=40) and experienced participants (n=41). The majority (73/81) confirmed realistic visualization of the lesions. The 3D impression was rated as “very good” in 64% of cases (52/81) and good in 31% (25/81). Overall, 86% (70/81) of the participants certified high clinical relevance of the phantom.
Conclusion The presented INVUS phantom concept allows standardized and realistic training for interventions.
The main challenge of ultrasound‐guided minimally invasive surgeries is to carry out treatments through small boreholes in the patient's body surface with sub‐millimetric accuracy and facility offered by ultrasound instruments. Thus, the phantoms' biomimetic appearances, acoustic characteristics, and mechanical properties are essential for healthcare professionals. In this study, gelatin and 3D‐printed photo‐resin phantoms were developed for hard and soft tissues, respectively. Using glutaraldehyde (GA) and formaldehyde (FA) to crosslink gelatin phantoms, the mechanical strength, ultrasound velocity, acoustic impedance, needle insertion forces, and antiseptic periods were improved, and the addition of silica nanoparticles raised the acoustic impedance. For 3D‐printed phantoms, the acoustic impedance ascended with hydrophilic polyethylene glycol diacrylate (PEGDA) oligomers. The additives applied in this study successfully made the gelatin and photo‐resin phantoms more mimetic to muscle and bone tissues, allowing their application in preoperative preparations. 3D‐printed photo‐resin phantoms were developed for hard and soft tissues. The additives of crosslinkers, nanoparticles, and reactive monomers improved the mechanical strength, acoustic properties, needle insertion forces, and antiseptic periods of phantoms efficiently.
Ultrasound-guided needle interventions are common procedures in medicine, and tissue-mimicking phantoms are widely used for simulation training to bridge the gap between theory and clinical practice in a controlled environment. This review assesses tissue-mimicking materials from 24 studies as candidates for a high-fidelity ultrasound phantom, including methods for evaluating relevant acoustic and mechanical properties and to what extent the reported materials mimic the superficial layers of biological tissue. Speed of sound, acoustic attenuation, Young's modulus, hardness, needle interaction forces, training efficiency and material limitations were systematically evaluated. Although gelatin and agar have the closest acoustic values to tissue, mechanical properties are limited, and strict storage protocols must be employed to counteract dehydration and microbial growth. Polyvinyl chloride (PVC) has superior mechanical properties and is a suitable alternative if durability is desired and some ultrasound realism to human tissue may be sacrificed. Polyvinyl alcohol (PVA), while also requiring hydration, performs well across all categories. Furthermore, we propose a framework for the evaluation of future ultrasound-guided needle intervention tissue phantoms to increase the fidelity of training programs and thereby improve clinical performance.
Medical ultrasound scanners are typically calibrated to the soft tissue
average of 1540 m s. In regions of different sound speed, for example,
organs and tumours, the B-scan image then becomes a distortion of the true
tissue cross-section, due to the misrepresentation of length and refraction. To
quantify this distortion we develop a general geometric ray model for an object
with an atypical speed of sound embedded in an ambient medium. We analyse the
ensuing area distortion for circular and elliptical objects, mapping it out as
a function of the key parameters, including the speed of sound mismatch, the
object size and its elongation. We find that the area distortion can become
significant, even for small-scale speed of sound mismatches. Our findings are
verified by ultrasound imaging of a test object.
Steering of needles involves the planning and timely modifying of instrument-tissue force interactions to allow for controlled deflections during the insertion in tissue. In this work, the effect of tip shape on these forces was studied using 10 mm diameter needle tips. Six different tips were selected, including beveled and conical versions, with or without pre-bend or pre-curve. A six-degree-of-freedom force/ torque sensor measured the loads during indentations in tissue simulants. The increased insertion (axial) and bending (radial) forces with insertion depth — the force-displacement slopes — were analyzed. Results showed that the ratio between radial and axial forces was not always proportional. This means that the tip load does not have a constant orientation, as is often assumed in mechanics-based steering models. For all tip types, the tip-load assumed a more radial orientation with increased axial load. This effect was larger for straight tips than for pre-bent or pre-curved tips. In addition, the force-displacement slopes were consistently higher for (1) increased tip angles, and for (2) beveled tips compared to conical tips. Needles with a bent or curved tip allow for an increased bending force and a decreased variability of the tip load vector orientation.
Agar phantoms are widely used as soft tissue mimics and some preparation techniques are described in the literature. There are also standards that describe the recipe of a soft tissue mimicking material (TMM). However some details of manufacture process are not clearly defined. The standardization of the phantom's preparation can produce a metrological impact on the results of the acoustic properties measured. In this direction, this paper presents a standard operating procedure (SOP) to prepare the agar TMM described on the IEC 60601-237.
Phantoms are physical constructs used in procedure planning, training, medical imaging research, and machine calibration. Depending on the application, the material a phantom is made out of is very important. With ultrasound imaging, phantom materials used need to have similar acoustic properties, specifically speed of sound and attenuation, as a specified tissue. Phantoms used with needle insertion require a material with a similar tensile strength as tissue and, if possible, the ability to self heal increasing its overall lifespan. Soft polyvinyl chloride (PVC) and silicone were tested as possible needle insertion phantom materials. Acoustic characteristics were determined using a time of flight technique, where a pulse was passed through a sample contained in a water bath. The speed of sound and attenuation were both determined manually and through spectral analysis. Soft PVC was determined to have a speed of sound of approximately 1395 m/s and attenuation of 0.441 dB/cm (at 1 MHz). For the silicone mixture, the respective speed of sound values was within a range of 964.7 m/s and 1250.0 m/s with an attenuation of 0.547 dB/cm (at 1 MHz).
The polyvinyl chloride (PVC) tissue-mimicking material for needle insertion was manufactured and evaluated. Factorial design of experiment was conducted by changing three factors − the ratio of softener and PVC polymer solution, the mass fraction of mineral oil, and the mass fraction of micro-sized glass beads − to study the indentation hardness, compression elastic modulus and friction and cutting forces in needle insertion of 12 types of soft PVC material. The indentation hardness of the soft PVC material ranged from 5 to 50. The elastic modulus of the soft PVC material was from 6 to 45kPa between 0-0.15 strain. The friction and cutting force during needle insertion also had large ranges, which were from 0.005 to 0.086N/mm and 0.04 to 0.36N respectively. The analysis of variance showed that the ratio of softener and PVC polymer solution had the most significant effect on all of the four properties of the PVC material. The percentage of mineral oil also had statistical significance on these four properties. The glass beads only had effect on the needle insertion cutting force. A nonlinear regression model was applied to find relationships among mechanical properties and the significant factors. The R2 values of the regression analysis results were all larger than 0.9. Four properties of a PVC tissue-mimicking material can be designed to desired values based on these relationships.
Ultrasound artifacts are encountered daily in clinical practice and may be a source of confusion on interpretation. Some artifacts arise secondary to improper scanning techniques and may be avoidable. Other artifacts are generated by the physical limitations of the technique. Recognition of artifacts is important, as they may be clues to tissue composition and aid in diagnosis. The ability to recognize and correct potential ultrasound artifacts is important for image-quality improvement and optimal patient care. In this article, we review common ultrasound artifacts that occur in B mode, spectral and color Doppler, and elastography. © 2013 Hindi et al, publisher and licensee Dove Medical Press Ltd.
The accuracy of a transient elastography liver-scanning ultrasound system was assessed using a novel application of PVA-cryogel as a tissue-mimicking material with acoustic and shear elasticity properties optimized to best represent those of liver tissue. Although the liver-scanning system has been shown to offer a safer alternative for diagnosing liver cirrhosis through stiffness measurement, as compared to the liver needle biopsy exam, the scanner's accuracy has not been fully established. Young's elastic modulus values of 5-6 wt% PVA-cryogel phantoms, also containing glycerol and 0.3 µm Al(2)O(3) and 3 µm Al(2)O(3), were measured using a 'gold standard' mechanical testing technique and transient elastography. The mechanically measured values and acoustic velocities of the phantoms ranged between 1.6 and 16.1 kPa and 1540 and 1570 m s(-1), respectively, mimicking those observed in liver tissue. The values reported by the transient elastography system overestimated Young's elastic modulus values representative of the progressive stages of liver fibrosis by up to 32%. These results were attributed to the relative rather than absolute nature of the measurement arising from the single-point acoustic velocity calibration of the system, rendering the measurements critically dependent on the speed of sound of the sample under investigation. Given the wide range of acoustic velocities which exist in the liver, spanning healthy tissue to cirrhotic pathology, coupled with the system's assumption that the liver is approximately elastic when it is rather highly viscoelastic, care should be exercised when interpreting the results from this system in patient groups.
1969 to 2003, 34 years.
Simulations are now in widespread use in medical education and medical personnel evaluation. Outcomes research on the use and effectiveness of simulation technology in medical education is scattered, inconsistent and varies widely in methodological rigor and substantive focus.
Review and synthesize existing evidence in educational science that addresses the question, 'What are the features and uses of high-fidelity medical simulations that lead to most effective learning?'.
The search covered five literature databases (ERIC, MEDLINE, PsycINFO, Web of Science and Timelit) and employed 91 single search terms and concepts and their Boolean combinations. Hand searching, Internet searches and attention to the 'grey literature' were also used. The aim was to perform the most thorough literature search possible of peer-reviewed publications and reports in the unpublished literature that have been judged for academic quality.
Four screening criteria were used to reduce the initial pool of 670 journal articles to a focused set of 109 studies: (a) elimination of review articles in favor of empirical studies; (b) use of a simulator as an educational assessment or intervention with learner outcomes measured quantitatively; (c) comparative research, either experimental or quasi-experimental; and (d) research that involves simulation as an educational intervention.
Data were extracted systematically from the 109 eligible journal articles by independent coders. Each coder used a standardized data extraction protocol.
Qualitative data synthesis and tabular presentation of research methods and outcomes were used. Heterogeneity of research designs, educational interventions, outcome measures and timeframe precluded data synthesis using meta-analysis. HEADLINE RESULTS: Coding accuracy for features of the journal articles is high. The extant quality of the published research is generally weak. The weight of the best available evidence suggests that high-fidelity medical simulations facilitate learning under the right conditions. These include the following: providing feedback--51 (47%) journal articles reported that educational feedback is the most important feature of simulation-based medical education; repetitive practice--43 (39%) journal articles identified repetitive practice as a key feature involving the use of high-fidelity simulations in medical education; curriculum integration--27 (25%) journal articles cited integration of simulation-based exercises into the standard medical school or postgraduate educational curriculum as an essential feature of their effective use; range of difficulty level--15 (14%) journal articles address the importance of the range of task difficulty level as an important variable in simulation-based medical education; multiple learning strategies--11 (10%) journal articles identified the adaptability of high-fidelity simulations to multiple learning strategies as an important factor in their educational effectiveness; capture clinical variation--11 (10%) journal articles cited simulators that capture a wide variety of clinical conditions as more useful than those with a narrow range; controlled environment--10 (9%) journal articles emphasized the importance of using high-fidelity simulations in a controlled environment where learners can make, detect and correct errors without adverse consequences; individualized learning--10 (9%) journal articles highlighted the importance of having reproducible, standardized educational experiences where learners are active participants, not passive bystanders; defined outcomes--seven (6%) journal articles cited the importance of having clearly stated goals with tangible outcome measures that will more likely lead to learners mastering skills; simulator validity--four (3%) journal articles provided evidence for the direct correlation of simulation validity with effective learning.
While research in this field needs improvement in terms of rigor and quality, high-fidelity medical simulations are educationally effective and simulation-based education complements medical education in patient care settings.
Tissue-mimicking phantoms are very useful in the field of tissue characterization and essential in elastography for the purpose of validating motion estimators. This study is dedicated to the characterization of polyvinyl alcohol cryogel (PVA-C) for these types of applications. A strict fabrication procedure was defined to optimize the reproducibility of phantoms having a similar elasticity. Following mechanical stretching tests, the phantoms were used to compare the accuracy of four different elastography methods. The four methods were based on a one-dimensional (1-D) scaling factor estimation, on two different implementations of a 2-D Lagrangian speckle model estimator (quasistatic elastography methods), and on a 1-D shear wave transient elastography technique (dynamic method). Young's modulus was investigated as a function of the number of freeze-thaw cycles of PVA-C, and of the concentration of acoustic scatterers. Other mechanical and acoustic parameters-such as the speed of sound, shear wave velocity, mass density, and Poisson's ratio-also were assessed. The Poisson's ratio was estimated with good precision at 0.499 for all samples, and the Young's moduli varied in a range of 20 kPa for one freeze-thaw cycle to 600 kPa for 10 cycles. Nevertheless, above six freeze-thaw cycles, the results were less reliable because of sample geometry artifacts. However, for the samples that underwent less than seven freeze-thaw cycles, the Young's moduli estimated with the four elastography methods showed good matching with the mechanical tensile tests with a regression coefficient varying from 0.97 to 1.07, and correlations R2 varying from 0.93 to 0.99, depending on the method.
Background:
There has been an explosive growth of ECPR within new and established ECMO programs worldwide with the concomitant need for simulation trainers. However, current commercially available ECMO simulation models are expensive and lack many standard cardiorespiratory resuscitative (CPR) features.
Objective:
To use 3-dimensional (3D) printing to develop a training manikin for comprehensive ECPR simulation.
Methods:
A standard commercially available CPR manikin with airway model was used as the base model for modification. An inexpensive 3D printer was used to print a modular plastic pelvis. A medical silicone gel incorporated silicone femoral vasculature component was manufactured with connection to a gravity fed vascular system.
Results:
The resulting modified manikin included the modular in-house designed ECMO cannulation and vascular structures wedded to the commercially available airway and CPR components. In simulation exercise involving first responders, paramedics, and emergency and critical care physicians, the model was reported as realistic with ultrasound views, cannulation, and resuscitative components functional. The entire cost for development of the ECMO component was estimated at 5 AUD per simulation run.
Conclusions:
A novel in-house modified manikin for ECPR was developed that was cost-efficient and realistic to use from first response through to establishment of ECMO circulation.
Ultrasound increases a first-attempt success rate for vascular access when considered by knowledgeable and experienced practitioners. Education and training of these practitioners in ultrasound-guided peripheral intravenous cannulation is becoming increasingly common, although no consensus has been reached regarding its curriculum. The current systematic literature review aims to explore different training modules and components in use, and its efficacy and efficiency in ultrasound-guided peripheral intravenous cannulation in hospitalized adults by different healthcare providers. Database search was performed from January 2009 to December 2018 for publications describing the training or education of healthcare professionals in ultrasound-guided peripheral intravenous cannulation in adult patients. Data-analyses was performed on 23 studies, concluding that competency on ultrasound-guided peripheral intravenous cannulation can be achieved after following a brief training in a fixed curriculum, consisting of a didactic training session, a simulated hands-on component, and is completed after a supervised live-case training. Lectures should focus on ultrasound physics, including the vascular anatomy. The hands-on training included identification of veins on a life model without cannulating, followed by cannulation of veins using a nonhuman tissue model. At the end, supervised cannulation of veins on the upper extremity with an ultrasound-guided technique was performed on live patients to show competency.
Ultrasound (US) elastography, or elasticity imaging, is an adjunct imaging technique that utilizes sequential US images of soft tissues to measure the tissue motion and infer or quantify the underlying biomechanical characteristics. For abdominal aortic aneurysms (AAA), biomechanical properties such as changes in the tissue's elastic modulus and estimates of the tissue stress may be essential for assessing the need for the surgical intervention. Abdominal aortic aneurysms US elastography could be a useful tool to monitor AAA progression and identify changes in biomechanical properties characteristic of high-risk patients. A preliminary goal in the development of an AAA US elastography technique is the validation of the method using a physically relevant model with known material properties. Here we present a process for the production of AAA tissue-mimicking phantoms with physically relevant geometries and spatially modulated material properties. These tissue phantoms aim to mimic the US properties, material modulus, and geometry of the abdominal aortic aneurysms. Tissue phantoms are made using a polyvinyl alcohol cryogel (PVA-c) and molded using 3D printed parts created using computer aided design (CAD) software. The modulus of the phantoms is controlled by altering the concentration of PVA-c and by changing the number of freeze-thaw cycles used to polymerize the cryogel. The AAA phantoms are connected to a hemodynamic pump, designed to deform the phantoms with the physiologic cyclic pressure and flows. Ultra sound image sequences of the deforming phantoms allowed for the spatial calculation of the pressure normalized strain and the identification of mechanical properties of the vessel wall. Representative results of the pressure normalized strain are presented. © 2018, Journal of Visualized Experiments. All rights reserved.
Image-guided interventions are widely employed in clinical medicine, which brings significant revolution in healthcare in recent years. However, it is impossible for medical trainees to experience the image-guided interventions physically in patients due to the lack of certificated skills. Therefore, training phantoms, which are normally tissue mimicking materials, are widely used in medical research, training, and quality assurance. This review focuses on the tissue mimicking materials used in image-guided needle-based interventions. In this case, we need to investigate the microstructure characteristics and mechanical properties (for needle intervention), optical properties and acoustical properties (for imaging) of these training phantoms to compare with the related properties of human real tissues. The widely used base materials, additives and the corresponding concentrations of the training phantoms are summarized from the literatures in recent ten years. The microstructure characteristics, mechanical behavior, optical properties and acoustical properties of the tissue mimicking materials are investigated, accompanied with the common experimental methods, apparatus and theoretical algorithm. The influence of the concentrations of the base materials and additives on these characteristics are compared and classified. In this review, we assess a comprehensive overview of the existing techniques with the main accomplishments, and limitations as well as recommendations for tissue mimicking materials used in image-guided needle-based interventions.
Introduction:
Training using ultrasound phantoms allows for safe introduction to clinical skills and is associated with improved in-hospital performance. Many materials have been used to simulate human tissue in phantoms including commercial manikins, agar, gelatin, and Ballistics Gel; however, phantom tissues could be improved to provide higher-fidelity ultrasound images or tactile sensation. This article describes a novel phantom tissue mixture of a modified polyvinyl chloride (PVC) polymer, mineral oil, and chalk powder and evaluates needle cutting and ultrasonic properties of the modified PVC polymer mixture compared with a variety of phantom tissues.
Methods:
The first experiment measured axial needle forces of a needle insertion into nine phantom materials, including three formulations of modified PVC. The second experiment used a pairwise comparison survey of ultrasound images to determine the perceived realism of phantom ultrasound images.
Results:
It was found that the materials of Ballistics Gel and one of the PVC mixtures provide stiff force feedback similar to cadaver tissue. Other phantom materials including agar and gelatin provide very weak unrealistic force feedback. The survey results showed the PVC mixtures being viewed as the most realistic by the survey participants, whereas agar and Ballistics Gel were seen as the least realistic.
Conclusions:
The realism in cutting force and ultrasound visualization was determined for a variety of phantom materials. Novel modified PVC polymer has great potential for use in ultrasound phantoms because of its realistic ultrasound imaging and modifiable stiffness. This customizability allows for easy creation of multilayer tissue phantoms.
Artifacts are frequently encountered at clinical US, and while some are unwanted, others may reveal valuable information related to the structure and composition of the underlying tissue. They are essential in making ultrasonography (US) a clinically useful imaging modality but also can lead to errors in image interpretation and can obscure diagnoses. Many of these artifacts can be understood as deviations from the assumptions made in generating the image. Therefore, understanding the physical basis of US image formation is critical to understanding US artifacts and thus proper image interpretation. This review is limited to gray-scale artifacts and is organized into discussions of beam- and resolution-related, location-related (ie, path and speed), and attenuation-related artifacts. Specifically, artifacts discussed include those related to physical mechanisms of spatial resolution, speckle, secondary lobes, reflection and reverberation, refraction, speed of sound, and attenuation. The underlying physical mechanisms and appearances are discussed, followed by real-world strategies to mitigate or accentuate these artifacts, depending on the clinical application. Relatively new US modes, such as spatial compounding, tissue harmonic imaging, and speckle reduction imaging, are now often standard in many imaging protocols; the effects of these modes on US artifacts are discussed. The ability of a radiologist to understand the fundamental physics of ultrasound, recognize common US artifacts, and provide recommendations for altering the imaging technique is essential for proper image interpretation, troubleshooting, and utilization of the full potential of this modality. (©)RSNA, 2017.
Poly(vinyl alcohol) (PVA) is a polymer of great interest because of its many desirable characteristics specifically for various pharmaceutical and biomedical applications. The crystalline nature of PVA has been of specific interest particularly for physically crosslinked hydrogels prepared by repeated cycles of freezing and thawing. This review includes details on the structure and properties of PVA, the synthesis of its hydrogels, the crystallization of PVA, as well as its applications. An analysis of previous work in the development of freezing and thawing processes is presented focusing on the implications of such materials for a variety of applications. PVA blends that have been developed with enhanced properties for specific applications will also be discussed briefly. Finally, the future directions involving the further development of freeze/thawed PVA hydrogels are addressed.
Silicone-based tissue-mimicking phantom is widely used as a surrogate of tissue for clinical simulators, allowing clinicians to practice medical procedures and researchers to study the performance of medical devices. This study investigates using the mineral oil in room-temperature vulcanizing silicone to create the desired mechanical properties and needle insertion characteristics of a tissue-mimicking phantom. Silicone samples mixed with 0, 20, 30, and 40 wt. % mineral oil were fabricated for indentation and needle insertion tests and compared to four types of porcine tissues (liver, muscle with the fiber perpendicular or parallel to the needle, and fat). The results demonstrated that the elastic modulus and needle insertion force of the phantom both decrease with an increasing concentration of mineral oil. Use of the mineral oil in silicone could effectively tailor the elastic modulus and needle insertion force to mimic the soft tissue. The silicone mixed with 40 wt. % mineral oil was found to be the best tissue-mimicking phantom and can be utilized for needle-based medical procedures.
The grinding procedure and setup, the cutting edge inclination and rake angles of the needle with lancet point (NLP), and the NLP tissue insertion force are investigated in this paper. The NLP is the most commonly used needle tip geometry. However, there is a lack of research on the NLP grinding and cutting edge characteristics. In this study, a four-step grinding procedure and a mathematical model to calculate the inclination and rake angles along the cutting edge of the NLP are developed. Three cases of NLP are defined based on the relative position of the lancets. Prototype NLP for each case was produced and analyzed. Compared to the regular bias bevel needle, grinding two lancets in NLP can increases the inclination angle, particularly at the needle tip. Experiments with needle insertion into the porcine liver were conducted and results showed that NLP could achieve over 40% reduction of the initial peak needle insertion force compared to that of the regular bias bevel needle tip.
A thorough understanding of needle–tissue interaction mechanics is necessary to optimize needle design, achieve robotically needle steering, and establish surgical simulation system. It is obvious that the interaction is influenced by numerous variable parameters, which are divided into three categories: needle geometries, insertion methods, and tissue characteristics. A series of experiments are performed to explore the effect of influence factors (material samples n=5 for each factor) on the insertion force. Data were collected from different biological tissues and a special tissue-equivalent phantom with similar mechanical properties, using a 1-DOF mechanical testing system instrumented with a 6-DOF force/torque (F/T) sensor. The experimental results indicate that three basic phases (deformation, insertion, and extraction phase) are existent during needle penetration. Needle diameter (0.7–3.2 mm), needle tip (blunt, diamond, conical, and beveled) and bevel angle (10–85°) are turned out to have a great influence on insertion force, so do the insertion velocity (0.5–10 mm/s), drive mode (robot-assisted and hand-held), and the insertion process (interrupted and continuous). Different tissues such as skin, muscle, fat, liver capsule and vessel are proved to generate various force cures, which can contribute to the judgement of the needle position and provide efficient insertion strategy.
Paraffin-gel waxes have been investigated as new soft tissue-mimicking materials for ultrasound-guided breast biopsy training. Breast phantoms were produced with a broad range of acoustical properties. The speed of sound for the phantoms ranged from 1425.4 ± 0.6 to 1480.3 ± 1.7 m/s at room temperature. The attenuation coefficients were easily controlled between 0.32 ± 0.27 dB/cm and 2.04 ± 0.65 dB/cm at 7.5 MHz, depending on the amount of carnauba wax added to the base material. The materials do not suffer dehydration and provide adequate needle penetration, with a Young's storage modulus varying between 14.7 ± 0.2 kPa and 34.9 ± 0.3 kPa. The phantom background material possesses long-term stability and can be employed in a supine position without changes in geometry. These results indicate that paraffin-gel waxes may be promising materials for training radiologists in ultrasound biopsy procedures.
A freezing-thawing process of aqueous poly(vinyl alcohol), (PVA) solutions was undertaken to study the supermolecular PVA structures produced. Aqueous solutions of 2,5 to 15 wt.-% PVA were frozen at −20°C for 45 to 120min and were subsequently thawed for long periods of time (up to 12h) at 23 ± 1°C. The transmittance of visible light was recorded as a function of thawing time. Determination of the parameters of the supermolecular particles in the PVA solutions was done by application of Klenin's theory. The average radii of the particles were in the order of 1,6–2,3 μm.Ein Gefrier-/Auftauprozeß von wäßrigen Poly(vinyl alcohol), (PVA)-Lösungen wurde angewendet, um die auftretenden übermolekularen PVA-Strukturen zu untersuchen. Wäßrige Lösungen von 2,5–15 Gew.-% PVA wurden für die Dauer von 45–120min bei −20°C zum Gefrieren gebracht und wurden anschließend für lange Zeitperioden (biszu 12h) bei 23 ± 1°C aufgetaut. Die Durchlässigkeit von sichtbarem Licht wurde als Funktion der Auftauzeit aufgezeichnet. Die Bestimmung der Parameter der übermolekularen Teilchen in den PVA Lösungen wurde durch Anwendung der Theorie von Klenin durchgeführt und ergab mittlere Radien in einer Größenordnung von 1,6–2,3 μm.
The development of needles, needle-insertion simulators, and needle-wielding robots for use in a clinical environment depends on a thorough understanding of the mechanics of needle-tissue interaction. It stands to reason that the forces arising from this interaction are influenced by numerous factors, such as needle type, insertion speed, and tissue characteristics. However, exactly how these factors influence the force is not clear. For this reason, the influence of various factors on needle insertion-force was investigated by searching literature for experimental data. This resulted in a comprehensive overview of experimental insertion-force data available in the literature, grouped by factor for quick reference. In total, 99 papers presenting such force data were found, with typical peak forces in the order of 1-10N. The data suggest, for example, that higher velocity tends to decrease puncture force and increase friction. Furthermore, increased needle diameter was found to increase peak forces, and conical needles were found to create higher peak forces than beveled needles. However, many questions remain open for investigation, especially those concerning the influence of tissue characteristics.
Phantoms are a vital step for the preliminary validation of new image-guided procedures. In this paper, the authors present a deformable prostate phantom for use with multimodal imaging (end-fire or side-fire ultrasound, CT and MRI) and more specifically for transperineal or transrectal needle-insertion procedures. It is made of soft polyvinyl chloride (PVC) plastic and includes a prostate, a perineum, a rectum, a soft periprostatic surrounding and embedded targets for image registration and needle-targeting. Its main particularity is its realistic deformability upon manipulation.
After a detailed manufacturing description, the imaging and mechanical characteristics of the phantom are described and evaluated. First, the speed of sound and stress-strain relationship of the PVC material used in the phantom are described, followed by an analysis of its storage, imaging, needle-insertion force, and deformability characteristics.
The average speed of sound in the phantom was measured to be 1380 ± 20 m/s, while the stress-strain relationship was found to be viscoelastic and in the range of typical prostatic tissues. The mechanical and imaging characteristics of the phantom were found to remain stable at cooler storage temperatures. The phantom had clearly distinguishable morphology in all three imaging modalities, with embedded targets that could be precisely segmented, resulting in an average US-CT rigid registration error of 0.66 mm. The mobility of the phantom prostate upon needle insertion was between 2 and 4 mm, with rotations between 0° and 2°, about the US probe head.
The phantom's characteristics compare favorably with in vitro and in vivo measurements found in the literature. The authors believe that this realistic phantom could be of use to researchers studying new needle-based prostate diagnosis and therapy techniques.
PVA has been proposed as a promising biomaterial suitable for tissue mimicking, vascular cell culturing and vascular implanting. In this research, a kind of transparent PVA hydrogel has been investigated in order to mimic the creatural soft tissue deformation during mini-invasive surgery with needle intervention, such as brachytherapy. Three kinds of samples with the same composition of 3 g PVA, 17 g de-ionized water, 80 g dimethyl-sulfoxide but different freeze/thaw cycles have been prepared. In order to investigate the structure and properties of polyvinyl alcohol hydrogel, micro-structure, mechanical property and deformation measurement have been conducted. As the SEM image comparison results show, with the increase of freeze/thaw cycles, PVA hydrogel revealed the similar micro-structure to porcine liver tissue. With uniaxial tensile strength test, the above composition with a five freeze/thaw cycle sample resulted in Young's modulus similar to that of porcine liver's property. Through the comparison of needle insertion deformation experiment and the clinical experiment during brachytherapy, results show that the PVA hydrogel had the same deformation property as prostate tissue. These transparent hydrogel phantom materials can be suitable soft tissue substitutes in needle intervention precision or pre-operation planning studies, particularly in the cases of mimicking creatural tissue deformation and analysing video camera images.
Ultrasound (US) use has rapidly entered the field of acute pain medicine and regional anesthesia and interventional pain medicine over the last decade, and it may even become the standard of practice. The advantages of US guidance over conventional techniques include the ability to both view the targeted structure and visualize, in real time, the distribution of the injected medication, and the capacity to control its distribution by readjusting the needle position, if needed. US guidance should plausibly improve the success rate of the procedures, their safety and speed. This article provides basic information on musculoskeletal US techniques, with an emphasis on the principles and practical aspects. We stress that for the best use of US, one should venture beyond the "pattern recognition" mode to the more advanced systematic approach and use US as a tool to visualize structures beyond the skin (sonoanatomy mode). We discuss the sonographic appearance of different tissues, introduce the reader to commonly used US-related terminology, cover basic machine "knobology" and fundamentals of US probe selection and manipulation. At the end, we discuss US-guided needle advancement. We only briefly touch on topics dealing with physics, artifacts, or sonopathology, which are available elsewhere in the medical literature.
The characterization and calibration of ultrasound imaging systems requires tissue-mimicking phantoms with known acoustic properties, dimensions and internal features. Tissue phantoms are available commercially for a range of medical applications. However, commercial phantoms may not be suitable in ultrasound system design or for evaluation of novel imaging techniques. It is often desirable to have the ability to tailor acoustic properties and phantom configurations for specific applications. A multitude of tissue-mimicking materials and phantoms are described in the literature that have been created using a variety of materials and preparation techniques and that have modeled a range of biological systems. This paper reviews ultrasound tissue-mimicking materials and phantom fabrication techniques that have been developed over the past four decades, and describes the benefits and disadvantages of the processes. Both soft tissue and hard tissue substitutes are explored.
Anatomic structures possessing varying sonic propagation velocities refract ultrasonic beams and create distortions in the sonographic image. The distortions consist of inaccurate positioning of echogenic locations (geometric distortions) and of inaccurate display of ultrasonic intensities (intensity distortions). Artifacts of both types occur in the region distal to a structure of circular cross section with an internal sonic propagation velocity lower than that of its surroundings. In an attempt to better understand these distortions, a model is developed from first principles of the production of sonograms of such a region. Assuming a uniform ultrasonic beam and uniform echogenicity of the surrounding tissue, a mathematical expression has been derived for the intensity of the sound arriving at each point and returning to the transducer. Computer simulations of the resulting sonographic image are provided for visualization. In spite of many simplifying assumptions, this model is shown to be consistent with several known artifacts, and provides insight into the mechanisms of their production.
A ghost artifact is produced when refraction of an ultrasound beam occurs in one part of a scanning plane. Image duplication or even triplication may result. This may lead to error of diagnosis and measurement. Ghost artifacts are commonly seen in transverse echograms of pelvic organs because the rectus muscle interposed between the transducer and the area of interest is acting as a lens and refracts the ultrasound beam. Three illustrative case reports are presented.
PIP
A ghost artifact is produced when refraction of an ultrasound beam occurs in 1 part of a scanning plane. Image duplication or even triplication may result, leading possibly to an error of diagnosis and measurement. Ghost artifacts are commonly seen in transverse echograms of pelvic organs because the rectus muscle interposed between the transducer and the area of interest is acting as a lens and refracts the ultrasound beam. 3 illustrative case reports are presented.
The authors present a unique application of polyvinyl alcohol (PVA) cryogel as an anthropomorphic, elastic, vascular phantom material that can be used in MR imaging. The composition consists of two nontoxic ingredients: water and PVA. The biomechanical and MR properties can be adjusted to be similar to those of excised porcine aortas by varying the number of freeze-thaw cycles to which the PVA solution is exposed. The authors present the T1, T2, shrinkage, and tensile properties of PVA cryogel tubes as a function of freeze-thaw cycles. MR images of a dual elastic aortic phantom undergoing pulsatile motion are shown.
A review was undertaken of physical phenomena and the values of associated physical quantities relevant to arterial ultrasound imaging and measurement. Arteries are multilayered anisotropic structures. However, the requirement to obtain elasticity measurements from the data available using ultrasound imaging necessitates the use of highly simplified constitutive models involving Young's modulus, E. Values of E are reported for healthy arteries and for the constituents of diseased arteries. It is widely assumed that arterial blood flow is Newtonian. However, recent studies suggest that non-Newtonian behavior has a strong influence on arterial flow, and the balance of published evidence suggests that non-Newtonian behavior is associated primarily with red cell deformation rather than with aggregation. Hence, modeling studies should account for red cell deformation and the shear thinning effect that this produces. Published literature in healthy adults gives an average hematocrit and high-shear viscosity of 0.44 ± 0.03 and 3.9 ± 0.6 mPa.s, respectively. Published data on the acoustic properties of arteries and blood is sufficiently consistent between papers to allow compilation and derivation of best-fit equations summarizing the behavior across a wide frequency range, which then may be used in future modeling studies. Best-fit equations were derived for the attenuation coefficient vs. frequency in whole arteries (R2 = 0.995), plasma (R2 = 0.963) and blood with hematocrit near 45% (R2 = 0.999), and for the backscatter coefficient vs. frequency from blood with hematocrit near 45% (R2 = 0.958). (E-mail: [email protected]
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Some expertise as well as hand-eye coordination is required to perform a successful sonographically guided breast biopsy. A simple phantom allows beginners to practice freehand, real-time sonographically guided needle biopsy, aspiration, core biopsy, and needle localization. Several homemade sonographic biopsy phantoms have been proposed, using agar,1-3 gelatin, 4-6 liver,7,8 and turkey breast.9 The addition of Metamucil (Proctor & Gamble, Cincinnati, OH) to gelatin results in an echogenic medium that resembles anatomic breast tissue to facilitate the teaching of freehand biopsy techniques of the breast.
Establishing the required components for training in ultrasoundguided peripheral intravenous cannulation: A systematic review of available evidence
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