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: A photoacoustic volume imaging (PAVI) system was designed to study breast cancer detection and diagnosis in the mammographic geometry in combination with automated 3-D ultrasound (AUS). The goal of the work described here was to validate the design and evaluate its performance in human breast tissues for non-invasive imaging of deeply positioned structures covering such geometry. The good penetration of near-infrared light and high receiving sensitivity of a broad-bandwidth, 572-element, 2-D polyvinylidene fluoride (PVDF) array at a low center frequency of 1 MHz were used with 20 channel simultaneous acquisition. Pseudo-lesions filled with dilute blood were imaged in three human breast specimens at various depths up to 49 mm. With near-infrared light illumination and 256-sample averaging, the extrapolated maximum depth in imaging a 2.4-mm blood-rich lesion with a 3-dB contrast-to-noise ratio in a compressed breast was 54 mm. Three-dimensional photoacoustic volume image stacks of the breasts were co-registered with 3-D ultrasound image stacks, suggesting for the first time that PAVI, based on the intrinsic tissue contrast, can visualize tissue interfaces other than those with blood, including the inner skin surface and connective tissue sheets. With the designed system, PAVI revealed satisfactory imaging depth and sensitivity for coverage of the entire breast when imaged from both sides in the mammographic geometry with mild compression.Ultrasound in medicine & biology 08/2013; · 2.46 Impact Factor
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ABSTRACT: A system incorporating automated 3-D ultrasound and digital X-ray tomosynthesis is being developed for improved breast lesion detection and characterization. The goal of this work is to develop and test candidates for a dual-modality mesh compression paddle. A Computerized Imaging Reference Systems (Norfork, VA, USA) ultrasound phantom with tilted low-contrast cylindrical objects was used. Polyester mesh fabrics (1- and 2-mm spacing), a high-density polyethylene filament grid (Dyneema, DSM Dyneema, Stanley, NC, USA) and a solid polymethylpentene (TPX; Mitsui Plastics, Inc., White Plains, NY) paddle were compared with no overlying structures using a GE Logic 9 (GE Healthcare, Waukesha, WI) with M12L transducer. A viscous gel provided coupling. The phantom was scanned 10 times over 9 cm for each configuration. Image volumes were analyzed for signal strength, contrast and contrast-to-noise ratio. X-ray tests confirmed X-ray transparency for all materials. By all measures, both mesh fabrics outperformed TPX and Dyneema, and there were essentially no differences between 2-mm mesh and unobstructed configurations.Ultrasound in medicine & biology 04/2014; · 2.46 Impact Factor