Accuracy of correlation function method for evaluating pulsed high intensity focused ultrasound

Objective To investigate the accuracy of ultrasound monitoring during pulsed high intensity focused ultrasound(PHIFU) treatment and improve the sensitivity of ultrasound monitoring of tissue necrosis caused by PHIFU treatment. Methods Bovine liver ex vivo was dot-exposed with HIFU at the therapeutic doses of 2000 J(group A) and 1440 J(group B). The two groups were further divided into groups A1(power 100 W,duty cycle 100%,irradiate 20 s) A2(power 100 W,duty cycle 50%,irradiate 40 s),A3(power 100 W,duty cycle 40%,irradiate 50 s),B1(power 120 W,duty cycle 100%,irradiate 12 s), B2(power 100 W,duty cycle 50%,irradiate 24 s),and B3(power 100 W,duty cycle 40%,irradiate 30 s).The gray scale changes in the ultrasonic images after the exposures were observed,and the correlation function of the image was calculated before and after the exposure.The accuracy of evaluations based on the correlation function and gray-scale changes was compared. Results The correct rate of gray scale-based evaluation of tissue necrosis caused by PHIFU was only 51%,while that by correlation function-based evaluation reached 85%.Conclusion Monitoring of tissue necrosis caused by PHIFU treatment can not rely solely on evaluation of gray-scale change of the ultrasound images,and the correlation function-based evaluation can be more accurate and sensitive for that purpose.