Effects of microwave tissue coagulation on the livers of normal rabbits: A comparison of findings of image analysis and histopathological examination

The livers of normal rabbits were subjected to microwave tissue coagulation (MTC), and comparison was made of the subsequent time-course changes in tissue observed on MRI, CT and histopathological examination. 16 rabbits were used. MTC was performed with a 21 gauge needle electrode inserted into the liver at laparotomy. 1-2 h after thermal coagulation, a region with slightly lower attenuation than that of surrounding normal liver parenchyma was observed on CT, and no enhancement was detected. With MRI, change from high signal intensity to iso-signal intensity from the inner zone to the margin was found on T-1 weighted images (T1WI), and heterogeneous high signal intensity was observed on T-2 weighted images (T2WI). On Gd-DTPA enhanced MRI, no enhancement occurred. 1-4 weeks after coagulation, the cellular structure at the site of coagulation was lost on histological examination, and the tissue became necrotic. On CT, homogeneous water density was observed, and no enhancement was detected. With MRI, regions of iso- or slightly low signal intensity were observed on T1WI, and regions of heterogeneous high to low signal intensity were seen on T2WI. After 1 week, a granulation layer consisting mainly of fibrous tissue 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. The ring-shaped enhancement was also noted on CT. MRI appears to be useful for observation of time-course changes following MTC therapy because of its sensitivity in the detection of tissue changes.