An Acoustic Backscatter-Based Method for Estimating Attenuation Towards Monitoring Lesion Formation in High Intensity Focused Ultrasound

This work investigated the transient characteristics of tissue attenuation coefficients before, during and after HIFU treatment at different total acoustic powers in ex vivo porcine muscle tissues. Initially, preliminary data for the changes in attenuation coefficient induced in ex vivo porcine muscle tissues due to coagulation were obtained. The data indicated that changes in least squares attenuation coefficient slope (Δβ) and attenuation coefficient intercept (Δα0) were both potentially reliable indicators of tissue thermal damage. Then, pulse-echo radiofrequency data were acquired to estimate Δβ and Δα0, and to construct Δβ, Δα0, and B-mode images. Dynamic changes of Δβ and Δα0 were correlated with conventional B-mode ultrasound images over the HIFU treatment process. During HIFU treatment, Δβ and Δα0 increased rapidly with the appearance of bubble clouds in the B-mode images, and bubble activities appeared as strong hyperechoic regions in the B-mode images, caused fluctuations in the estimated Δβ and Δα0 values. After the treatment, Δβ and Δα0 gradually decreased, accompanied by fadeout of hyperechoic spot in the B-mode images, until they were stable at 10 minutes post-treatment, at 0.84 ± 0.11 [dB/(MHz.cm)] and 1.36 ± 0.19 [dB/cm], respectively. Finally the results showed that Δβ and Δα0 images had significantly higher contrast to speckle ratios than the conventional B-mode images.