Evaluation of thin compression paddles for mammographically compatible ultrasound
ABSTRACT We are developing a combined digital mammography/3D ultrasound system for breast cancer imaging to better detect and/or characterize breast lesions. Scanning a GE Logiq 9 M12L transducer array over a mammographic compression paddle/plate introduces an attenuating layer with sound speed and impedance different from that of tissue. This reduces signal level and affects beam focusing, Making the choice of a suitable paddle is essential for accurate sonographic detection of lesions. Similar work has been reported, but we present a more complete characterization of image quality through mammographic paddles of varying materials, (e.g., Lexan, Polyurethane, TPX, Mylar) and thicknesses. Quantitative measures such as spatial and contrast resolution, signal strength, and range lobe levels were compared to images without a paddle. In vivo patient studies compared images with standard handheld scans to images with 0.25, 1.0, and 2.5 mm thick paddles to examine restricted access problems, coupling issues, and overall lesion clarity. For mammography, filters were added to account for differences in X-ray transmission properties between the tested paddle and the standard mammography paddle. When lateral beamforming corrections were implemented to partially account for the speed of sound through the paddles, experiments conducted on 25 μm line targets with several plastic paddles between 0.25-2.5 mm thick demonstrated image quality measures close to those with no paddle present. In some paddles <1.0 mm thick, a worst-case 5% reduction in linear spatial resolution and a maximum 4 dB signal loss averaged over 4 cm occurred. In those better paddles up to 2.5 mm thick, range lobe levels were consistently 35-40 dB lower than the signal maximum. Areas of restricted access (such as near the chest wall) were minimized by imaging in trapezoidal (virtual convex) format. TPX paddles <2.5 mm were the most ideal for ultrasound and mammogram imaging requirements and, after accounting for signal loss through the paddle, appearance of cysts was comparable to images obtained from handheld, direct contact sweeps.
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ABSTRACT: We have produced high quality strain images in a breast phantom and in 7 human subjects with 3D ultrasound (US) breast elastography using a combined US/tomography system. All radiofrequency (RF) images in this study were acquired using a GE Logiq 9 scanner and a linear 1D array operating at 7.5 MHz on a stand-alone, mammography-mimicking unit. To determine 3D elastography efficacy, a breast phantom (ATS BB-1) was imaged using static compression at 0.5% axial steps up to 2.5% strain over 7-17 elevational steps with slice thicknesses 15-60% of the elevational beamwidth. RF images were correlated using 3D, phase-sensitive speckle tracking algorithms and accumulated, estimated displacements were converted to strain images. Image quality was assessed via correlation coefficient (R) and strain contrast-to-noise ratio (CNR). Results indicated that R remained high and nearly constant (0.96-0.98) for a 0.5% strain step under all conditions. Elevational slice thicknesses of les 30% of the elevational beamwidth sizes produced the highest CNR because thicker slices did not sufficiently meet Nyquist requirements. At slice thicknesses of 35% elevational beamwidth, at least 7 elevational slices were required to meet 3D speckle tracking algorithm spatial requirements in the elevational direction (filter ges kernel = 1 elevational speckle spot). Moving beyond these minimum requirements produced the greatest improvement in CNR with 3D tracking: acquiring elevational planes over 3 speckle spots produced a 90% CNR improvement over 2D analogous. Acquiring up to 4.5 speckle spots (17 elevational planes) increased the CNR by a total of 130%. Additionally, elevational slices off the center axis confirmed on-axis results. Human subject motion was addressed before applying these results in vivo. Volume data acquisition must occur within a patient breath hold (les 10 sec). Thus, all 7 human subjects (1 cancer, 6 fibroadenomas) were imaged using quasistatic elastography as they held their brea- th. Five axial compression steps were acquired at 0.3-0.7% strain for 7-11 elevational planes with slice thicknesses 30% of the elevational beamwidth (spatially equivalent to 2.0-4.6 speckle spots). When minimal out-of-plane motion was present, there was no significant difference in correlation coefficient values created from 3D and fast (<0.5 sec) 2D acquisition. Thus, potential motion artifacts introduced by 3D data acquisition have been minimized. Of the 7 lesions imaged, 3 were visible on both 3D and 2D and elastograms, with the 3D elastograms depicting CNR<sub>epsiv</sub> of 7-11% better than 2D. This suggests that 3D elastography on the combined system holds great potential for improving an already clinically valuable imaging techniqueUltrasonics Symposium, 2006. IEEE; 11/2006
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ABSTRACT: This study evaluated the utility of 3D automated ultrasound in conjunction with 3D digital X-Ray tomosynthesis for breast cancer detection and assessment, to better localize and characterize lesions in the breast. Tomosynthesis image volumes and automated ultrasound image volumes were acquired in the same geometry and in the same view for 27 patients. 3 MQSA certified radiologists independently reviewed the image volumes, visually correlating the images from the two modalities with in-house software. More sophisticated software was used on a smaller set of 10 cases, which enabled the radiologist to draw a 3D box around the suspicious lesion in one image set and isolate an anatomically correlated, similarly boxed region in the other modality image set. In the primary study, correlation was found to be moderately useful to the readers. In the additional study, using improved software, the median usefulness rating increased and confidence in localizing and identifying the suspicious mass increased in more than half the cases. As automated scanning and reading software techniques advance, superior results are expected.Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2007; 2007:1335-8. DOI:10.1109/IEMBS.2007.4352544
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ABSTRACT: Damage to the circulatory system resulting from ischemia-reperfusion injury (I/R injury) occurs during heart attacks and hemorrhagic shock. The authors report a method for mitigating microcirculatory injury, using diagnostic frequency continuous-mode ultrasound and how effects are influenced by nitric oxide production impairment. Five groups of hamsters were studied using the dorsal skin fold window chamber: (1) I/R; (2) I/R + ultrasound during ischemia; (3) I/R + ultrasound after ischemia; (4) I/R + N(omega)-nitro-L-arginine methyl ester (L-NAME); and (5) I/R + L-NAME + ultrasound. Functional capillary density (FCD) and microvascular diameter, flow velocity, and flow were monitored. During the exposures 2.49 MHz continuous ultrasound was used. Significant improvements in animals exposed to ultrasound after ischemia were found at 24 h of reperfusion in FCD, arteriolar diameter, and arteriolar and venular flow velocity and flow. Animals exposed to ultrasound during ischemia showed significantly improved FCD. L-NAME treatment reduced the improvement of microvascular function, compared to animals exposed after ischemia. The use of continuous-mode diagnostic frequency ultrasound is beneficial in preventing long-term ischemia-reperfusion effects in the microcirculation as shown by the return of microvascular parameters to baseline values, an effect not attained in the absence of ultrasound treatment. The effects may be in part due to the production of nitric oxide consequent to locally induced shear stress effects by ultrasound exposure.Microcirculation 09/2007; 14(6):571-82. DOI:10.1080/10739680701410280