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.