Non-invasive estimation of temperature using diagnostic ultrasound during high intensity focused ultrasound therapy

Abstract

The use of HIFU for thermal ablation of human tissues requires safe real-time monitoring of the lesion formation during the treatment to avoid damage of the surrounding healthy tissues and to control temperature rise. Besides MR imaging, several methods have been proposed for temperature imaging using diagnostic ultrasound, and echoshift estimation (using speckle tracking) is the most promising technique. It is based on the thermal dependence of the ultrasound echo that accounts for two different physical phenomena: local change in speed of sound and thermal expansion of the propagating medium due to changes in temperature. In our experiments we have used two separate transducers: HIFU exposure was performed using a 1.06 MHz single element focusing transducer of 64 mm aperture and 63.2mm focal length; the ultrasound diagnostic probe of 11 MHz operated in B-mode for image guidance. The temperature measurements were performed in an agar-based tissue-mimicking phantom complying with the specification given in IEC60601-2-5. To verify the obtained results, the numerical modeling of the acoustic and temperature fields was carried out using KZK and Pennes Bioheat equations. The comparison of the results simulated and measured, as well as measured with thermocouples, shows a rather good coincidence.