Ultrasound phase contrast thermal imaging with reflex transmission imaging methods in tissue phantoms

Thermal imaging measurements using ultrasound phase contrast have been performed in tissue phantoms heated with a focused ultrasound source. Back projection and reflex transmission imaging principles were used to detect sound speed-induced changes in the phase caused by an increase in the temperature. The temperature was determined from an empirical relationship for the temperature dependence on sound speed. The phase contrast was determined from changes in the sound field measured with a hydrophone scan conducted before and during applied heating. The lengthy scanning routine used to mimic a large two-dimensional array required a steady-state temperature distribution within the phantom. The temperature distribution in the phantom was validated with magnetic resonance (MR) thermal imaging measurements. The peak temperature was found to agree within 1 degrees C with MR, and good agreement was found between the temperature profiles. The spatial resolution was 0.3x0.3x0.3mm, comparing favorably with the 0.625x0.625x1.5-mm MR spatial resolution.