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Random field for medical ultrasound

Ulrich, Ines Elisa, Boehm, Christian, Fichtner, Andreas

Ines Elisa Ulrich, Christian Boehm, Andreas Fichtner, "Random field interferometry for medical ultrasound," Proc. SPIE 11319, Medical Imaging 2020: Ultrasonic Imaging and Tomography, 1131912 (16 March 2020); doi: 10.1117/12.2559852 Event: SPIE Medical Imaging, 2020, Houston, Texas, United States

Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 25 Mar 2020 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use Random field interferometry for medical ultrasound

Ines Elisa Ulrich, Christian Boehm and Andreas Fichtner Department of Earth Sciences, ETH Z¨urich, Sonneggstrasse 5, CH-8092 Z¨urich, Switzerland

ABSTRACT We present a novel approach to obtain time-of-flight measurements between transducer pairs in an Ultrasound computed tomography (USCT) scanner by applying the interferometry principle, which has been used success- fully in seismic imaging to recover the subsurface velocity structure from ambient noise recordings. To apply this approach to a USCT aperture, random wavefields are generated by activating the emitting transducers in a random sequence. By correlating the random signals recorded by the receiving transducers, we obtain an approximation of the Green’s functions between all receiver pairs, where one is acting as a virtual source. This eliminates specific source imprints, and thus avoids the need for reference measurements and calibration. The retrieved Green’s functions between any two measurement locations can then be used as new data to invert the sound speed map. On the basis of the cross-correlation travel times a ray-based time-of-flight tomography is developed and solved with an iterative least-squares method. As a proof of concept, the algorithm is tested on numerical breast phantoms in a synthetic 2D study. Keywords: Random field interferometry, ultrasound computed tomography, time-of-flight inversion

1. INTRODUCTION Ultrasound computed tomography (USCT) is frequently used for medical purposes to image soft tissue body parts, as for instance the breast. The property of interest is the speed of sound of the breast tissue, tissue density or attenuation. Commonly, malignant cell regions are denser and stiffer than benign regions, thus speed of sound maps image breast tissue.1–3 Breast cancer detection using USCT usually works with a collection of ultrasound scans that measure the pressure wavefield emitted by individual transducers. A state-of-the-art USCT acquisition process often requires a large number of emitter-receiver pairs to obtain a good coverage of the domain of interest and careful calibration of the emitting transducers using reference measurements in water.4–6 This is a time-consuming process during which patient movements can degrade the quality of the aquired data. Furthermore, calibration of emitters using reference measurements in water is often subject to strong assumptions, for instance, that the temperature of the water is uniform and constant, which are difficult to establish during real-life aquisition. In recent years, scientific contributions from geophysical research have proven to be a fruitful addition to the medical imaging community. Although the imaged medium in the geophysical application compared to the medical application seems considerably different, Pratt et al.7,8 have shown the possibilities arising from applying geophysical imaging methods to breast cancer screening. Further studies, extending the research to image other human body parts such as the brain9 or the limbs,10 have demonstrated the potential of ultrasound imaging. With this work, we propose to circumvent the aforementioned challenges of standard USCT data acquisition techniques by transferring yet another theory widely applied in seismic imaging, to breast imaging