Quantitative characterization of the ultrasound thermal strains in tissue mimicking phantoms with different oil concentrations

Ultrasound thermal strain imaging (US-TSI) has been known for the capability of tissue characterization according to distinct sound speed change in different tissues when temperature increases. US-TSI for detecting lipids in atherosclerosis plaques and fatty livers has previously been reported while some practical challenges were not fully addressed, especially due to physiological motions. To overcome such limitation, we recently developed an ultrasound transducer that combines an acoustic heating array and an imaging array to achieve US-TSI with heating performed in a region of approximately 10 mm by 5 mm by 2 mm within a very short time period of about 50 ms compared both cardiac and breathing motions. To characterize the new US-TSI probe, a thorough benchtop investigation was performed on the relationship among the threekey variables for TSI: thermal strain, temperature increase, and lipid concentration. In the experiments, homogeneous oil-in-gelatin phantoms of different oil concentrations were fabricated to simulate different lipid-plaque concentrations. Temperature curves were recorded by a thermal couple with millisecond-level time constant. Thermal strains were computed by developed US-TSI signal processing procedures. The results build a tissue-temperature-strain model and calibrate the new US-TSI probe for in vivo atherosclerosis plaque characterization.