Charles W. Manry, Jr. Shira L. Broschat
School of Elec. Eng. & Comput. Sci., Washington State Univ., Pullman, WA 99164-2752
The incidence of breast cancer is increasing. In 1961 a woman had a 1 in 20 change of getting breast cancer; today it is 1 in 9. The earlier a tumor is detected, the more likely the survival of the victim. Thus it is critical that high-resolution breast imaging techniques be developed that are capable of detecting small tumors. One modality under consideration is ultrasound imaging. Algorithms developed for ultrasound imaging usually assume that scattering of energy in the breast is weak, allowing simple and efficient image formation algorithms. However, experiments conducted at the University of Pennsylvania suggest that fat lobes near the breast's surface refract ultrasound energy as it passes through the breast. This strong refraction violates the weak scattering assumption and calls into question the validity of algorithms using this approximation. A higher-order finite-difference time-domain (FDTD) algorithm has been developed that can be used to model the effects of fat lobes on the propagation and scattering of an ultrasound pulse in the human breast. The simple breast model used is two-dimensional with a fat structure similar to that of the Pennsylvania study. Results support the conclusion that refraction in the breast poses a significant challenge to ultrasound imaging. [Work supported by NSF.]