Optimized Beamforming and Limited Angle Tomography of the Compressed Breast

Breast cancer is one of the most predominant forms of cancer, comprising of 22.9% of all cancers in women, causing approximately 450,000 deaths in 2008. The conventional imaging standard procedure for screening studies encompasses mammography followed by handheld ultrasound. However, there is a decrease in specificity and sensitivity when imaging younger women with dense breast tissue. This dissertation will investigate ultrasound grayscale, speed of sound, and attenuation imaging of the compressed breast to improve current screening procedure. Enabling improved efficiency in 3D volume B-mode imaging would remove operator dependency on acquiring ultrasound data and improve diagnosis because handheld ultrasound sometimes is focused on a different lesion compared to the suspicious one found on the mammogram. Beamforming algorithms for use in reconfigurable arrays were investigated. A transmit beam with an extended depth of focus was developed by minimizing a cost function that reduced the side lobe energy while maximizing the depth of focus generated by the beam. Optimized channel selection of subelements in reconfigurable arrays was illustrated in order to remove excess side lobe energy caused by overall phase delay across the aperture. Speed of sound and attenuation imaging represent different imaging modes and have been shown to increase sensitivity and specificity in breast imaging studies. In the compressed breast, these transmission modes have limited views similar to those in X-ray tomosynthesis, resulting in a major streaking artifact in the axial direction. Using a regularized cost function, a priori information was used to aid the speed of sound and attenuation inversion to produce images with minimal streaking artifacts. The speed of sound images were employed in a forward model to produce attenuation coefficient images with only speed of sound artifacts, allowing creation of attenuation images representative of the bulk properties of the different tissues in the breast, i.e., including attenuation from local absorption and internal isotropic scattering of the ultrasonic energy independent of the acoustic properties of surrounding tissues.PhDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91430/1/fongming_1.pd