MRI evaluation of thermal ablation of tumors with focused ultrasound

MRI was used to target and evaluate the tissue effects of focused ultrasoun d ablation on tumors implanted in the skeletal muscle of rabbits in vivo. F irst, MRI was used to localize the tumors and plan the ultrasound therapy, Second, temperature-sensitive phase-difference images were acquired to moni tor the location of the ultrasound focus and to estimate the effects of tem perature rise. After the treatment, the spatial and temporal temperature pr ofiles for defining boundaries of tissue coagulation were calculated, Final ly, these boundaries were compared to Ta-weighted and contrast-enhanced T1- weighted images obtained immediately after therapy. The results indicate th at using MRI for planning and evaluating focused ultrasound surgery is feas ible. We showed a linear relationship between applied power and shifts in t he proton resonant frequency, Fluctuations in the location of the focus abo ut the target location were on the order of the resolution of the MR images , The temperature rise and lesion size varied significantly. Regions of tis sue coagulation calculated from MR data correlated well with post-therapy i maging.