Towards Non-invasive Ultrasonic Characterization of Carotid Atherosclerotic Plaque

Vulnerable atherosclerotic plaques are thought to be prone to rupture due to various compositional and morphological factors. One key characteristic is thought to be the presence of a soft, lipid rich core in the plaque. Acoustic radiation force impulse (ARFI) and thermal strain imaging (TSI) are non-invasive ultrasound-based imaging modalities. ARFI imaging measures the tissue response to an ultrasonically generated mechanical perturbation. In TSI, the tissue temperature is increased and image contrast is a result of the temperature and composition dependence of the speed of sound.\ud \ud Initial efforts to develop a TSI system utilized two separate ultrasound transducers for heating and imaging. We developed signal processing to improve estimates of thermal strain obtained from this system and showed that TSI could be used to detect lipids in ex vivo human arterial tissue samples. However, the translational obstacles encountered by this system outweighed the potential imaging utility.\ud \ud In order to address these challenges, we developed temporally interleaved multi-foci beamforming which could be implemented on a standard imaging array to generate a broad, homogeneous ultrasound beam for either ARFI pushing or TSI heating. We showed that this beamforming approach could enable simultaneous acquisition of ARFI and thermal strain data while substantially improving the frame rate for ARFI imaging.\ud \ud In order to better understand the factors that affect signal quality in TSI and ARFI imaging, we conducted separate phantom studies for each imaging modality. We showed that with a temperature rise