Ultrasonic Imaging (ULTRASONIC IMAGING)

Publications in this journal

• Article: Quantitative Assessment of In Vivo Breast Masses Using Ultrasound Attenuation and Backscatter.

  Kibo Nam, James A Zagzebski, Timothy J Hall
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  ABSTRACT: Clinical analysis of breast ultrasound imaging is done qualitatively, facilitated with the ultrasound breast imaging-reporting and data system (US BI-RADS) lexicon, which helps to standardize imaging assessments. Two descriptors in that lexicon, "posterior acoustic features" and the "echo pattern" within a mass, are directly related to quantitative ultrasound (QUS) parameters, namely, ultrasound attenuation and the average backscatter coefficient (BSC). The purpose of this study was to quantify ultrasound attenuation and backscatter in breast masses and to investigate these QUS properties as potential differential diagnostic markers. Radio frequency (RF) echo signals were from patients with breast masses during a special ultrasound imaging session prior to core biopsy. Data were also obtained from a well characterized phantom using identical system settings. Masses include 14 fibroadenomas and 10 carcinomas. Attenuation for the acoustic path lying proximal to the tumor was estimated offline using a least squares method with constraints. BSCs were estimated using a reference phantom method (RPM). The attenuation coefficient within each mass was assessed using both the RPM and a hybrid method, and effective scatterer diameters (ESDs) were estimated using a Gaussian form factor model. Attenuation estimates obtained with the RPM were consistent with estimates done using the hybrid method in all cases except for two masses. The mean slope of the attenuation coefficient versus frequency for carcinomas was 20% greater than the mean slope value for the fibroadenomas. The product of the attenuation coefficient and anteroposterior dimension of the mass was computed to estimate the total attenuation for each mass. That value correlated well with the BI-RADS assessment of "posterior acoustic features" judged qualitatively from gray scale images. Nearly all masses were described as "hypoechoic," so no strong statements could be made about the correlation of echo pattern findings in BI-RADS with the averaged BSC values. However, most carcinomas exhibited lower values for the frequency-average BSC than fibroadenomas. The mean ESD alone did not differentiate the mass type, but fibroadenomas had greater variability in ESDs within the ROI than that found for invasive ductal carcinomas. This study demonstrates the potential to use attenuation and QUS parameters associated with the BSC as quantitative descriptors.
  Ultrasonic Imaging 04/2013; 35(2):146-161.
• Article: Ultrasonic Characterization of the Upper Trapezius Muscle in Patients with Chronic Neck Pain.

  Diego Turo, Paul Otto, Jay P Shah, Juliana Heimur, Tadesse Gebreab, Maryam Zaazhoa, Katherine Armstrong, Lynn H Gerber, Siddhartha Sikdar
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  ABSTRACT: Myofascial trigger points (MTrPs) are palpable, tender nodules in taut bands of skeletal muscle that are painful on compression. MTrPs are characteristic findings in myofascial pain syndrome (MPS). The role of MTrPs in the pathophysiology of MPS is unknown. Localization, diagnosis, and clinical outcome measures of painful MTrPs can be improved by objectively characterizing and quantitatively measuring their properties. The goal of this study was to evaluate whether ultrasound imaging and elastography can differentiate symptomatic (active) MTrPs from normal muscle. Patients with chronic (>3 months) neck pain with spontaneously painful, palpable (i.e., active) MTrPs and healthy volunteers without spontaneous pain (having palpably normal muscle tissue) were recruited for this study. The upper trapezius muscles in all subjects were imaged, and the echotexture was analyzed using entropy filtering of B-mode images. Vibration elastography was performed by vibrating the muscle externally at 100 Hz. Color Doppler variance imaging was used to quantify the regions of color deficit exhibiting low vibration amplitude. The imaging measures were compared against the clinical findings of a standardized physical exam. We found that sites with active MTrPs (n = 14) have significantly lower entropy (p < 0.05) and significantly larger nonvibrating regions (p < 0.05) during vibration elastography compared with normal, uninvolved muscle (n = 15). A combination of both entropy analysis and vibration elastography yielded 69% sensitivity and 81% specificity in discriminating active MTrPs from normal muscle. These results suggest that active MTrPs have more homogeneous texture and heterogeneous stiffness when compared with normal, unaffected muscle. Our methods enabled us to improve the imaging contrast between suspected MTrPs and surrounding muscle. Our results indicate that in subjects with chronic neck pain and active MTrPs, the abnormalities are not confined to discrete isolated nodules but instead affect the milieu of the muscle surrounding palpable MTrPs. With further refinement, ultrasound imaging can be a promising objective method for characterizing soft tissue abnormalities associated with active MTrPs and elucidating the role of MTrPs in the pathophysiology of MPS.
  Ultrasonic Imaging 04/2013; 35(2):173-187.
• Article: Viscoelastic Properties of Rodent Mammary Tumors Using Ultrasonic Shear-Wave Imaging.

  Yue Wang, Michael F Insana
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  ABSTRACT: Images of tumor mechanical properties provide important insights into malignant-cell processes manifest by extracellular matrix (ECM) stiffening and remodeling. This article presents a pilot study measuring in vivo mechanical-property characteristics of rodent mammary tumors using an ultrasonic shear-wave imaging technique. Shear waves are generated by a needle inserted into the tumor of anesthetized rodents that is vibrated harmonically between 50 and 450 Hz. Particle motion in the tumor associated with the radiation of cylindrical shear waves is imaged using pulsed-Doppler ultrasound techniques. Estimating the spatial gradient of shear-wave phase along the direction of propagation at frequencies in the measurement range yields shear-speed dispersion curves. Measured dispersion curves were fit to those predicted by three different rheological models to estimate the elastic and viscous coefficients of the complex shear modulus. The investigation was performed in vivo on four rat-mammary fibroadenoma tumors and five xenograft mouse-mammary carcinoma tumors. Each tumor was subsequently excised for histological imaging and composition analysis. Collagen composition was measured using hydroxyproline assays that were then correlated with mechanical measurements. The goal was to relate soft-tissue mechanical behavior to biological characteristics of tumor structures, specifically the collagenous ECM protein content. The choice of rheological model and the effects of artifacts induced by shear-wave reflections at internal tissue boundaries are carefully examined in this article. Addressing these issues is of great importance when selecting force-excitation methods and modulus estimation method to assess intrinsic tissue properties responsible for disease-specific elastographic contrast.
  Ultrasonic Imaging 04/2013; 35(2):126-145.
• Article: Letter from the Editor.

  Melvin Linzer
  Ultrasonic Imaging 04/2013; 35(2):75.
• Article: Single Tracking Location Methods Suppress Speckle Noise in Shear Wave Velocity Estimation.

  Etana C Elegbe, Stephen A McAleavey
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  ABSTRACT: In ultrasound-based elastography methods, the estimation of shear wave velocity typically involves the tracking of speckle motion due to an applied force. The errors in the estimates of tissue displacement, and thus shear wave velocity, are generally attributed to electronic noise and decorrelation due to physical processes. We present our preliminary findings on another source of error, namely, speckle-induced bias in phase estimation. We find that methods that involve tracking in a single location, as opposed to multiple locations, are less sensitive to this source of error since the measurement is differential in nature and cancels out speckle-induced phase errors.
  Ultrasonic Imaging 04/2013; 35(2):109-125.
• Article: Method for Estimating Total Attenuation from a Spatial Map of Attenuation Slope for Quantitative Ultrasound Imaging.

  Alexander D Pawlicki, William D O'Brien
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  ABSTRACT: Estimating total ultrasound attenuation from backscatter data is essential in the field of quantitative ultrasound (QUS) because of the need to compensate for attenuation when estimating the backscatter coefficient and QUS parameters. This work uses a reference phantom method of attenuation estimation to create a spatial map of attenuation slope (AS) from backscatter radio-frequency (RF) data of three phantoms and a rat mammary adenocarcinoma tumor (MAT). The attenuation maps show changes in attenuation between different regions of the phantoms and the MAT tumor. Analyses of the attenuation maps of the phantoms suggest that the AS estimates are in good quantitative agreement with the known values for the phantoms. Furthermore, estimates of total attenuation from the attenuation maps are likewise in good quantitative agreement with known values.
  Ultrasonic Imaging 04/2013; 35(2):162-172.
• Article: Variance and Covariance of Accumulated Displacement Estimates.

  Matthew Bayer, Timothy J Hall
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  ABSTRACT: Tracking large deformations in tissue using ultrasound can enable the reconstruction of nonlinear elastic parameters, but poses a challenge to displacement estimation algorithms. Such large deformations have to be broken up into steps, each of which contributes an estimation error to the final accumulated displacement map. The work reported here measured the error variance for single-step and accumulated displacement estimates using one-dimensional numerical simulations of ultrasound echo signals, subjected to tissue strain and electronic noise. The covariance between accumulation steps was also computed. These simulations show that errors due to electronic noise are negatively correlated between steps, and therefore accumulate slowly, whereas errors due to tissue deformation are positively correlated and accumulate quickly. For reasonably low electronic noise levels, the error variance in the accumulated displacement estimates is remarkably constant as a function of step size, but increases with the length of the tracking kernel.
  Ultrasonic Imaging 04/2013; 35(2):90-108.
• Article: An Approach to Unbiased Subsample Interpolation for Motion Tracking.

  Matthew M McCormick, Tomy Varghese
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  ABSTRACT: Accurate subsample displacement estimation is necessary for ultrasound elastography because of the small deformations that occur and the subsequent application of a derivative operation on local displacements. Many of the commonly used subsample estimation techniques introduce significant bias errors. This article addresses a reduced bias approach to subsample displacement estimations that consists of a two-dimensional windowed-sinc interpolation with numerical optimization. It is shown that a Welch or Lanczos window with a Nelder-Mead simplex or regular-step gradient-descent optimization is well suited for this purpose. Little improvement results from a sinc window radius greater than four data samples. The strain signal-to-noise ratio (SNR) obtained in a uniformly elastic phantom is compared with other parabolic and cosine interpolation methods; it is found that the strain SNR ratio is improved over parabolic interpolation from 11.0 to 13.6 in the axial direction and 0.7 to 1.1 in the lateral direction for an applied 1% axial deformation. The improvement was most significant for small strains and displacement tracking in the lateral direction. This approach does not rely on special properties of the image or similarity function, which is demonstrated by its effectiveness with the application of a previously described regularization technique.
  Ultrasonic Imaging 04/2013; 35(2):76-89.
• Article: Volumetric Thermoacoustic Imaging over Large Fields of View.

  M A Roggenbuck, R D Walker, J W Catenacci, S K Patch
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  ABSTRACT: The thermoacoustic (TA) contrast mechanism relies on rapid tissue heating and subsequent thermal expansion. TA computerized tomography (TCT) is therefore inverse source imaging. The TA contrast mechanism provides information complementary to that revealed by current diagnostic imaging techniques, but has been limited to just a few centimeters depth penetration. In this article, whole organ TCT is demonstrated on a large swine kidney. TA sinograms show that TA signal generated by high-power, very high frequency (VHF) electromagnetic pulses is detectable after travel through 6 cm of soft tissue. Reconstructed images provide resolution sufficient to track progression of calyces throughout the kidney. Because VHF electromagnetic energy can easily penetrate the abdomen of large adults, our results indicate that whole organ TA imaging is feasible in vivo, provided an ultrasound array can be placed near the region of interest. Pulses of 22 to 25 kW with carrier frequency 108 MHz and 900 ns pulse width were applied at a 100-Hz pulse repetition frequency to generate a 13-kV/m electric field and TA signal. Only 2 to 5 mJ was absorbed in the kidney per pulse, causing temperature and pressure jumps of only 5e-6°C and 4 Pa averaged throughout the 141-g specimen. TA pulses were detected by focused, single-element transducers (V306, Panametrics), amplified by 54 dB and averaged 64 times to reduce electronic noise. Data were measured over a cylindrical measurement aperture of radius 5 cm and length 6 cm, by rotating the specimen 1.8 degrees between tomographic views and translating 2 mm between slices. Reconstruction via filtered backprojection yields in-plane resolution better than 5 mm, but suffers significant blurring between planes. Both in-plane resolution and slice sensitivity profile could be improved by applying shorter irradiation pulsewidths and using less directional transducers. Both hardware changes would be recommended for a clinical prototype.
  Ultrasonic Imaging 01/2013; 35(1):57-67.
• Article: Vector quantization of RF channel data for ultrasound imaging.

  Pei-Ching Huang, Pai-Chi Li
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  ABSTRACT: Quantization is a necessary step in a digital beamformer that should be implemented efficiently when designing an ultrasound imaging system. Several factors should be considered, including the accuracy of both amplitude and phase in the digital representation, the quantization efficiency, and the complexity of the quantization scheme. While uniform scalar quantization (SQ) is currently used in most ultrasound imaging systems, this study used simulations and experimental data to explore vector quantization (VQ) based on the signals received by adjacent elements of the transducer array generally being strongly correlated. The signal-to-quantization-noise ratio, focusing quality, and accuracy in phase aberration correction and blood velocity estimation were assessed. The results show that using VQ instead of conventional SQ reduces the quantization noise by 10 dB with minimal degradation in the focusing quality. Similarly, the performance of correlation-based phase aberration correction was not affected at this level of quantization. Nevertheless, velocity estimation accuracy was found to be more susceptible to VQ noise when the reduction in the number of bits is limited to a factor of two. One benefit of using a more efficient quantizer is the reduced data size, which directly affects the data transfer rate and is an important design consideration for a digital imaging system.
  Ultrasonic Imaging 01/2013; 35(1):3-16.
• Article: Delineation of atherosclerotic plaque using subharmonic imaging filtering techniques and a commercial intravascular ultrasound system.

  Anush Sridharan, John R Eisenbrey, Priscilla Machado, Ebo D Demuinck, Marvin M Doyley, Flemming Forsberg
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  ABSTRACT: The ability to delineate atherosclerotic plaque from the surrounding tissue using custom-developed subharmonic imaging (SHI) digital filtering techniques was investigated in vivo using a commercially available system. Atherosclerosis was induced in the aorta of two Watanabe Heritable Hyperlipidemic rabbits following which injections of an ultrasound contrast agent (UCA) Definity (Lantheus Medical Imaging, N Billerica, Massachusetts) were administered. Imaging was performed using a Galaxy intravascular ultrasound (IVUS) scanner (Boston Scientific, Natick, Massachusetts) equipped with an Atlantis® SR Pro Imaging Catheter (Boston Scientific). Four preliminary band-pass filters were designed to isolate the subharmonic signal (from surrounding tissue) and applied to the radio-frequency (RF) data. Preliminary filter performances were compared in terms of vessel-tissue contrast-to-tissue ratio (CTR) and visual examination. Based on preliminary results, a subharmonic adaptive filter and a stopband (SB) filter were designed and applied to the RF data. Images were classified as fundamental, SHI, and SB. Four readers performed qualitative analysis of 168 randomly selected images (across all three imaging modes). The images were scored for overall image quality, image noise, plaque visualization, and vessel lumen visualization. A Wilcoxon signed-rank test was used to compare the scores followed by intraclass correlation (ICC) evaluation. Quantitative analysis was performed by calculating the CTRs for the vessel-to-plaque and vessel-to-tissue (compared using a paired student's t test). Qualitative analysis showed SHI and SB to have significantly less image noise relative to the fundamental mode (p < 0.001). Fundamental mode scored significantly higher than SHI and SB for the remaining three categories. ICC showed mixed results among reader evaluation for delineation of plaque. However, quantitatively, SHI produced the best vessel-plaque CTR.
  Ultrasonic Imaging 01/2013; 35(1):30-44.
• Article: Postmastoidectomy effusion measurement using a delay-line ultrasound transducer: cadaver experiments.

  Chin-Kuo Chen, Yung-Liang Wan, Jui Fang, Chien-Huang Lin, Wen-Ta Chiu, Po-Hsiang Tsui
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  ABSTRACT: Mastoidectomy is a surgical procedure for removing mastoid air cells and has been used widely to establish drainage and cleaning infections from the mastoid bone. Computed tomography (CT) and magnetic resonance imaging (MRI) are the primary instruments used to clinically detect mastoid effusion following surgery. This study examines the feasibility of ultrasonography to detect postsurgical mastoid effusion. In vitro ultrasound measurements were conducted on 10 cadavers. For each sample, mastoidectomy was performed, and saline and whole blood samples were injected into the surgical mastoid cavity to simulate different effusion properties. A 2.25-MHz delay-line ultrasound transducer was used to obtain ultrasound backscattered data from the mastoid. The data were used to analyze echo intensity and the backscattered statistics by estimating the scaling and Nakagami parameters of the Nakagami distribution model. The results show that the scaling and Nakagami parameters can successfully detect mastoid effusion. Specifically, the Nakagami parameter is capable of characterizing the mastoid effusion properties. This indicates that ultrasound measurement based on a combination of delay-line transducer and Nakagami parameter estimation is a potential real-time diagnostic tool for evaluating mastoid effusion following mastoidectomy without radiation exposure.
  Ultrasonic Imaging 01/2013; 35(1):45-56.
• Article: Intracranial Dual-Mode IVUS and Hyperthermia Using Circular Arrays: Preliminary Experiments.

  Vivek Patel, Edward Light, Carl Herickhoff, Gerald Grant, Gavin Britz, Christy Wilson, Mark Palmeri, Stephen Smith
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  ABSTRACT: In this study, we investigated the feasibility of using 3.5-Fr (3 Fr = 1 mm) circular phased-array intravascular ultrasound (IVUS) catheters for minimally invasive, image-guided hyperthermia treatment of tumors in the brain. Feasibility was demonstrated in two ways: (1) by inserting a 3.5-Fr IVUS catheter through skull burr holes, for 20 MHz brain imaging in the pig model, and (2) by testing a modified circular array for therapy potential with 18.5-MHz and 9-MHz continuous wave (CW) excitation. The imaging transducer's performance was superior to our previous 9-MHz mechanical IVUS prototype. The therapy catheter transducer was driven by CW electrical power at 18.5 MHz, achieving temperature changes reaching +8°C at a depth of 2 mm in a human glioblastoma grown on the flank of a mouse with minimal transducer resistive heating of +2°C. Further hyperthermia trials showed that 9-MHz CW excitation produced temperature changes of +4.5°C at a depth of 12 mm-a sufficient temperature rise for our long-term goal of targeted, controlled drug release via thermosensitive liposomes for therapeutic treatment of 1-cm-diameter glioblastomas.
  Ultrasonic Imaging 01/2013; 35(1):17-29.
• Article: Comparison of Ultrasound Attenuation and Backscatter Estimates in Layered Tissue-Mimicking Phantoms among Three Clinical Scanners.

  Kibo Nam, Ivan M Rosado-Mendez, Lauren A Wirtzfeld, Goutam Ghoshal, Alexander D Pawlicki, Ernest L Madsen, Roberto J Lavarello, Michael L Oelze, James A Zagzebski, William D O'Brien, Timothy J Hall
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  ABSTRACT: Backscatter and attenuation coefficient estimates are needed in many quantitative ultrasound strategies. In clinical applications, these parameters may not be easily obtained because of variations in scattering by tissues overlying a region of interest (ROI). The goal of this study is to assess the accuracy of backscatter and attenuation estimates for regions distal to nonuniform layers of tissue-mimicking materials. In addition, this work compares results of these estimates for "layered" phantoms scanned using different clinical ultrasound machines. Two tissue-mimicking phantoms were constructed, each exhibiting depth-dependent variations in attenuation or backscatter. The phantoms were scanned with three ultrasound imaging systems, acquiring radio frequency echo data for offline analysis. The attenuation coefficient and the backscatter coefficient (BSC) for sections of the phantoms were estimated using the reference phantom method. Properties of each layer were also measured with laboratory techniques on test samples manufactured during the construction of the phantom. Estimates of the attenuation coefficient versus frequency slope, α(0), using backscatter data from the different systems agreed to within 0.24 dB/cm-MHz. Bias in the α(0) estimates varied with the location of the ROI. BSC estimates for phantom sections whose locations ranged from 0 to 7 cm from the transducer agreed among the different systems and with theoretical predictions, with a mean bias error of 1.01 dB over the used bandwidths. This study demonstrates that attenuation and BSCs can be accurately estimated in layered inhomogeneous media using pulse-echo data from clinical imaging systems.
  Ultrasonic Imaging 10/2012; 34(4):209-21.
• Article: In vivo classification of breast masses using features derived from axial-strain and axial-shear images.

  Haiyan Xu, Tomy Varghese, Jingfeng Jiang, James A Zagzebski
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  ABSTRACT: Breast cancer is currently the second leading cause of cancer deaths in women. Early detection and accurate classification of suspicious masses as benign or malignant is important for arriving at an appropriate treatment plan. In this article, we present classification results for features extracted from ultrasound-based, axial-strain and axial-shear images of breast masses. The breast-mass stiffness contrast, size ratio, and a normalized axial-shear strain area feature are evaluated for the classification of in vivo breast masses using a leave-one-out classifier. Radiofrequency echo data from 123 patients were acquired using Siemens Antares or Elegra clinical ultrasound systems during freehand palpation. Data from four different institutions were analyzed. Axial displacements and strains were estimated using a multilevel, pyramid-based two-dimensional cross-correlation algorithm, with final processing block dimensions of 0.385 mm × 0.507 mm (three A-lines). Since mass boundaries on B-mode images for 21 patients could not be delineated (isoechoic), the combined feature analysis was only performed for 102 patients. Results from receiver operating characteristic (ROC) demonstrate that the area under the curve was 0.90, 0.84, and 0.52 for the normalized axial-shear strain, size ratio, and stiffness contrast, respectively. When these three features were combined using a leave-one-out classifier and support vector machine approach, the overall area under the curve improved to 0.93.
  Ultrasonic Imaging 10/2012; 34(4):222-36.
• Article: A method for direct localized sound speed estimates using registered virtual detectors.

  Brett C Byram, Gregg E Trahey, Jørgen A Jensen
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  ABSTRACT: Accurate sound speed estimates are desirable in a number of fields. In an effort to increase the spatial resolution of sound speed estimates, a new method is proposed for direct measurement of sound speed between arbitrary spatial locations. The method uses the sound speed estimator developed by Anderson and Trahey. Their least squares fit of the received waveform's curvature provides an estimate of the wave's point of origin. The point of origin and the delay profile calculated from the fit are used to arrive at a spatially registered virtual detector. Between a pair of registered virtual detectors, a spherical wave is propagated. By beamforming the data, the time-of-flight between the two virtual sources can be calculated. From this information, the local sound speed can be estimated. Validation of the estimator is made using phantom and simulation data. The set of test phantoms consisted of both homogeneous and inhomogeneous media. Several different inhomogeneous phantom configurations were used for the physical validation. The simulation validation focused on the limits of target depth and signal-to-noise ratio on virtual detector registration. The simulations also compare the impact of two- and three-layer inhomogeneous media. The phantom results varied based on signal-to-noise ratio and geometry. The results for all cases were generally less than 1% mean error and standard deviation. The simulation results varied somewhat with depth and F/#, but primarily, they varied with signal-to-noise ratio and geometry. With two-layer geometries, the algorithm has a worst-case spatial registration bias of 0.02%. With three-layer geometries, the axial registration error gets worse with a bias magnitude up to 2.1% but is otherwise relatively stable over depth. The stability over depth of the bias in a given medium still allows for accurate sound speed estimates with a mean relative error less than 0.2%.
  Ultrasonic Imaging 07/2012; 34(3):159-80.
• Article: High-frequency annular array fabrication using a flex circuit matching layer.

  Holly S Lay, Eric A Simpson, Greg Griffin, Geoffrey R Lockwood
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  ABSTRACT: Fabricating arrays for high-frequency image applications such as ophthalmic imaging, intravascular imaging, and small animal imaging is challenging. For example, an array for intravascular imaging must be small enough to fit within the lumen of a catheter and inexpensive enough to be discarded after a single use. This article presents a new method for fabricating high-frequency annular arrays that is simple and inexpensive. The annular array elements are defined by the electrode pattern on a back surface of a polyimide quarter-wavelength matching layer that is glued to the front face of a ceramic transducer substrate (PZT5H). Electrical losses associated with bonding the matching layer to the transducer substrate are reduced by fabricating a second set of electrodes on the transducer substrate and then bonding the substrates using an anisotropic conductive epoxy. The feasibility of this technique was established by fabricating a seven-element, 20-MHz, 5-mm diameter annular array. The prototype array produced a pulse with a -6-dB factional bandwidth of 50%, an insertion loss of 22 dB, and secondary lobes in the radiation pattern at f/2 that decreased to -65 dB with respect to the main lobe with a peak amplitude of -53 dB.
  Ultrasonic Imaging 07/2012; 34(3):196-204.
• Article: Echocardiographic-based assessment of myocardial fiber structure in individual, excised hearts.

  Michelle L Milne, Gautam K Singh, James G Miller, Mark R Holland
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  ABSTRACT: The objective of this study was to assess the feasibility of using echocardiographic imaging as an approach for determining the myocardial fiber structure of intact, individual hearts. Seven formalin-fixed, ex vivo sheep hearts were imaged using a commercially available echocardiographic imaging system, and the intrinsic fiber structure for the reconstructed short-axis cross section was determined for a specific distance from the apex of each heart. Diffusion tensor magnetic resonance (DT-MR) images of each heart were acquired and fiber maps were created for comparison with the fiber structure obtained from the corresponding reconstructed echocardiographic images. These two methods of obtaining the fiber structure showed relatively good agreement, suggesting that measurements of fiber orientation for individual hearts can be derived from echocardiographic images. Further development of this method may provide a clinically useful approach for mapping the fiber orientation in individual patients over the heart cycle.
  Ultrasonic Imaging 07/2012; 34(3):129-41.
• Article: A 5-MHz cylindrical dual-layer transducer array for 3-D transrectal ultrasound imaging.

  Yuling Chen, Man Nguyen, Jesse T Yen
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  ABSTRACT: Two-dimensional transrectal ultrasound (TRUS) is being used in guiding prostate biopsies and treatments. In many cases, the TRUS probes are moved manually or mechanically to acquire volumetric information, making the imaging slow, user dependent, and unreliable. A real-time three-dimensional (3-D) TRUS system could improve reliability and volume rates of imaging during these procedures. In this article, the authors present a 5-MHz cylindrical dual-layer transducer array capable of real-time 3-D transrectal ultrasound without any mechanically moving parts. Compared with fully sampled 2-D arrays, this design substantially reduces the channel count and fabrication complexity. This dual-layer transducer uses PZT elements for transmit and P[VDF-TrFE] copolymer elements for receive, respectively. The mechanical flexibility of both diced PZT and copolymer makes it practical for transrectal applications. Full synthetic aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics Data Acquisition System. Offline 3-D beamforming was then performed to obtain volumes of two wire phantoms and a cyst phantom. Generalized coherence factor was applied to improve the contrast of images. The measured -6-dB fractional bandwidth of the transducer was 62% with a center frequency of 5.66 MHz. The measured lateral beamwidths were 1.28 mm and 0.91 mm in transverse and longitudinal directions, respectively, compared with a simulated beamwidth of 0.92 mm and 0.74 mm.
  Ultrasonic Imaging 07/2012; 34(3):181-95.