Microwave coagulation therapy: Ex vivo comparison of MR imaging and histopathology

We compared the findings of magnetic resonance (MR) images and pathological examination to determine whether or not MR images reflect pathological cha nges following microwave coagulation therapy (MCT) on liver tissue. We used microwave (generating frequency 2450 Mhz, wave length 12 cm, output 50 W, 60 second duration) to irradiate six canine livers under general anesthesia . After the animals were sacrificed, the livers were resected, The irradiat ed regions were cut with margins and divided into two pieces, one for MR st udy, and the other for pathological examination. The findings were compared . From the center to the marginal layer, the irradiated region presented 4/ 3 laminal patterns on T1/T2-weighted images: low/ high, high/low, very high /high, and iso-low/high intensity. On gradient-echo imaging, the irradiated regions presented no decreasing signals using several echo time lengths. W ith hematoxylin and eosin stain, MR laminar patterns reflected the histopat hological changes, as follows: a tissue loss area surrounding the inserted needle, low/high: decreased sinusoidal width with/without necrotic tissue, high/low; sinusoidal width dilation at the periphery, very high/high; and f atty degenerated tissue surrounding the irradiated area at the boundary of the normal hepatocytes, iso-low/high. The MR signal intensity, which reflec ted the histopathological changes, presented tissue characterization after MCT, and the macromolecular hydration effect influenced the high intensity on T1-weighted images, (C) 2000 Wiley-Liss, Inc.