MR imaging of the liver after microwave coagulation. Experimental study in rabbits

The liver of normal rabbits was subjected to microwave tissue coagulation (MTC), and comparison was made of the subsequent time-course changes in tissue observed on MRI and histopathological examination. Shortly after MTC, with MRI, change from high signal intensity to iso-signal intensity from the inner zone to the margin was found on T1WI, and heterogeneous high signal intensity was observed on T2WI. On Gd-DTPA enhanced MRI, no enhancement was detected. One to four weeks after MTC, the cellular structure in the site of coagulation was lost on histological examination, and the tissue became necrotic. With MRI, regions of iso- or slightly low signal intensity were observed on T1WI, and regions of heterogeneous high to low signal intensity was observed on T2WI. After one week, a granulation layer consisting mainly of fibrous tissue growth developed, and a ring-shaped enhancement was observed in the low signal intensity region on T1WI and in the high signal intensity region on T2WI. MRI appears to be useful for observation of time-course changes following MTC therapy because of its sensitivity in detection of tissue changes. (author)