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: Although simple cysts are easily identified using sonography, description and management of nonsimple cysts remains uncertain. This study evaluated whether the correlation coefficient differences between breast tissue and lesions, obtained from 2D breast elastography, could potentially distinguish nonsimple cysts from cancers and fibroadenomas. We hypothesized that correlation coefficients in cysts would be dramatically lower than surrounding tissue because noise, imaging artifacts, and particulate matter move randomly and decorrelate quickly under compression, compared with solid tissue. For this preliminary study, 18 breast lesions (7 nonsimple cysts, 4 cancers, and 7 fibroadenomas) underwent imaging with 2D elastography at 7.5 MHz through a TPX (a polymethyl pentene copolymer) 2.5 mm mammographic paddle. Breasts were compressed similar to mammographic positioning and then further compressed for elastography by 1 to 7%. Images were correlated using 2D phase-sensitive speckle tracking algorithms and displacement estimates were accumulated. Correlation coefficient means and standard deviations were measured in the lesion and adjacent tissue, and the differential correlation coefficient (DCC) was introduced as the difference between these values normalized to the correlation coefficient of adjacent tissue. Mean DCC values in nonsimple cysts were 24.2 +/- 11.6%, 5.7 +/- 6.3% for fibroadenomas, and 3.8 +/- 2.9 % for cancers (p < 0.05). Some of the cysts appeared smaller in DCC images than gray-scale images. These encouraging results demonstrate that characterization of nonsimple breast cysts may be improved by using DCC values from 2D elastography, which could potentially change management options of these cysts from intervention to imaging follow-up. A dedicated clinical trial to fully assess the efficacy of this technique is recommended.Ultrasound in Medicine & Biology 02/2008; 34(1):12-21. · 2.46 Impact Factor
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ABSTRACT: Ischemia reperfusion (IR) injury, occurring during heart attacks, hemorrhagic shock, and bypass and transplant surgeries, impairs microcirculatory function and nitric oxide (NO) synthesis. We report the regulation of endothelial and inducible NO synthase (eNOS and iNOS) proteins as a consequence of the application of continuous mode diagnostic frequency ultrasound application following IR injury. Animals were assigned to one of five groups for microcirculatory assessment or Western blot analysis (WB) as follows: (1) IR+iNOS inhibition (1400W); and (2) IR+1400W+ultrasound for microcirculatory assessment, (3) Control; (4) IR; and (5) IR+ultrasound for WB. Functional capillary density and microvascular diameter, flow velocity, and flow were monitored for microcirculatory assessment. Skin tissue samples were harvested for WB. 2.49MHz continuous ultrasound was used for application. Both the inhibition of iNOS alone and iNOS inhibition with ultrasound irradiation positively influenced the microcirculation of observed animals relative to baseline values. Ultrasound exposure resulted in a significant production of eNOS protein in skin tissue harvested 24h into reperfusion (p<0.01). iNOS levels from the same tissue of ultrasound exposed animals were found to be significantly decreased 0.5h into reperfusion (p<0.05). Protection from lasting IR injury effects in the microcirculation, with continuous mode diagnostic frequency ultrasound, results from augmented eNOS protein levels during late reperfusion. Ultrasound inhibited iNOS protein production during early reperfusion may also confer protection from IR injury.Ultrasonics Sonochemistry 06/2008; 16(1):197-203. · 3.52 Impact Factor
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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. · 2.76 Impact Factor