Objective: To observe the appearance of fat necrosis in pig model after radio frequency ablation on MRI and to study the relevant pathologic basis. Methods: The model of fat necrosis was made in superficial fat layer of five pigs by radio frequency ablation, MRI including T1WI, T2WI, T2STIR, PWI and T1WI contrast-enhanced scan were performed at different times(from seven days to six months) after radio frequency ablation one week. The MRI findings in fat necrosis model was analyzed and compared with pathological results. Results: 22 lesions of fat necrosis were made in 5 pigs. Based on pathological features, the evolution of fat necrosis was divided into three stages. 22 lesions manifested heterogeneous low intensity which were in different degree in T1WI and T2WI, ring-shaped lower intensity was found in periphery of fat necrosis lesions. As the time went, the signal intensity of fat necrosis lesions was lower in T1WI and T2WI, patchy and dot-linear high signal were found in part of fat necrosis lesions; 22 lesions manifested high intensity in T2STIR and the signal intensity was lower lightly. Perfusion curves were rapid ascending and slow descending, there was not rapid ascending and rapid descending. The enhancement characteristic of fat necrosis was mainly early ring enhancement, and mainly in the late heterogeneous mild enhancement. Histopathlolgically, it was characterized by anuclear fat cells surrounded by phagocytic lipid-laden histiocytes(foam cells) initially, with an accumulation of multinucleated giant cells and fibroblast at the edges of the lesion. During the subsequent reparative phase, fibrosis may replace the areas of necrotic fat and debris. Conclusion: The MRI findings in fat necrosis model is characteristic, and can reflect the pathological features. |
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