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Abstract Pulsed high intensity focused ultrasound (HIFU) induced hyperthermia effects (39-44 ?C) have been regarded as a promising therapeutic tool for boosting immune responses or enhancing drug delivery into solid tumor. However, previous studies also reported that the cell death occurred when cells were maintained at 43 ?C for greater than 20 minutes. The aim of this study was to investigate the thermal responses inside in vivo rabbit auricular veins exposed to pulsed HIFU (1.17 MHz frequency, 5300 W/cm2 ISPPA) with relatively low duty ratios (0.2%-4.3%). The results show that: (1) with constant PRF (e.g., 1Hz), the thermal responses inside the vessel will increase with the increasing duty ratio; (2) a temperature elevation to 43 ?C can be identified at the duty ratio of 4.3%; (3) with constant duty ratios, the change of PRF will not significantly affect the temperature measurements in the vessel; and (4) as the duty ratios lower than 4.3%, the presence of microbubbles will not significantly enhance the thermal responses in the vessel, but will benefit HIFU-induced inertial cavitation events.
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