Breast ultrasound has been used in the USA primarily as an adjunct breast cancer diagnosis to projection x-ray mammography or DBT. Ultrasound is employed in screening in most of the world and its use for such dense breast is increasing in the USA. In either application, finding corresponding masses in images from both x-ray and ultrasound is time-consuming and prone to correlation errors, leading to delays in cancer diagnosis. Previously, we have shown that, when automated breast ultrasound is performed through a special mammographic paddle in the same or slightly reduced compression as the x-ray exam, such correlation errors were reduced<sup> [1-2]</sup>. Even for hand-controlled scanning, it should be useful to track the physical position and orientation of the ultrasound transducer in the coordinates of the x-ray to help in reducing both exam time and correlation errors in mass identification. A tracking system for hand scanning through a mesh mammographic paddle is achieved via the coordination of a full-HD camera and a 6-axis sensor, locates the path of the real time ultrasound image plane through the x-ray image or image stack. The tracking system requires minimal setup, with the camera mounted to a fixed location relative to the paddle and the 6-axis sensor attached to the transducer body. The tracking system can achieve an overall frame rate of 5 Hz and mean position error within 6.62mm. In a parallel display, a mass identified in the x-ray image volume will be used to generate trajectories for an ultrasound transducer to reach the same mass. Feasible, improved position tracking should allow creation of spliced 3D volumes and precise, multimodality image fusion.
In B-mode imaging of the dependent or compressed breast, wave incidence at steep angles can change propagation directions and induce areas of signal dropout. To evaluate the image anomalies in reasonable simulation times, we performed full-wave studies for center frequencies of 1 and 4 MHz. Speed of sound and density of skin, typical coupling gel, and adipose tissue were assigned to the test couplant. Compared with commercial gel, skin-like couplant reduced the dropout area at 1 and 4 MHz by 57.1% and 96.7%, respectively, consistent with a decreased average beam deflection in the breast. Conversely, the adipose-like couplant increased the dropout area from that of simulated commercial gel by 26.5% and 36.7% at 1 and 4 MHz, respectively. In addition, the skin-like couplant resulted in the greatest beam deflection inside the breast among all couplants. The findings could aid the use of three-dimensional simulations to design ultrasound couplants for beam passage through tissue boundaries at steep angles to improve corrections of signal dropout and defocusing and in compound imaging.
In B-mode images from dual-sided ultrasound, it has been shown that by delineating structures suspected of being
relatively homogeneous, one can enhance limited angle tomography to produce speed of sound images in the same view
as X-ray Digital Breast Tomography (DBT). This could allow better breast cancer detection and discrimination, as well
as improved registration of the ultrasound and X-ray images, because of the similarity of SOS and X-ray contrast in the
breast. However, this speed of sound reconstruction method relies strongly on B-mode or other reflection mode
segmentation. If that information is limited or incorrect, artifacts will appear in the reconstructed images. Therefore, the
iterative speed of sound reconstruction algorithm has been modified in a manner of simultaneously utilizing the image
segmentations and removing most artifacts. The first step of incorporating a priori information is solved by any nonlinearnonconvex
optimization method while artifact removal is accomplished by employing the fast split Bregman method to
perform total-variation (TV) regularization for image denoising. The proposed method was demonstrated in simplified
simulations of our dual-sided ultrasound scanner. To speed these computations two opposed 40-element ultrasound linear
arrays with 0.5 MHz center frequency were simulated for imaging objects in a uniform background. The proposed speed
of sound reconstruction method worked well with both bent-ray and full-wave inversion methods. This is also the first
demonstration of successful full-wave medical ultrasound tomography in the limited angle geometry. Presented results
lend credibility to a possible translation of this method to clinical breast imaging.