MR appearances of radiofrequency thermal ablation region: histopathologic correlation with dog liver models and an autopsy case

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate the utility of magnetic resonance (MR) imaging for indicating the extent of true tissue necrosis of the liver after radiofrequency (RF) ablation in comparison with histopathologic findings in dog models and an autopsy case. MATERIALS AND METHODS: RF ablation of the liver parenchyma was performed on three dogs under general anesthesia. MR appearances of the RF-ablated regions on T1-weighted fast-low angle shot (FLASH; repetition time/echo time [TR/TE]/flip angle: 120/3.8/70),T2-weighted turbo spin echo (3000/80/echo train = 25) and contrast-enhanced T1-weighted images were compared with histopathologic findings. An autopsy case with hepatocellular carcinoma was also enrolled in this study. RESULTS: All ablated regions showed three zones on T1-weighted FLASH images: a central zone with low intensity, a broad hyperintense middle zone, and a surrounding hypointense band. The central and middle zones corresponded to the degrees of coagulation necrosis observed during histopathologic examination, whereas no viable cells were seen in these zones during the microscopic examination using nicotinamide adenine dinucleotide diaphorase stain. The surrounding hypointense band corresponded to sinusoidal congestion in the acute phase and to fibrotic change in the subacute phase. CONCLUSION: MR imaging using the FLASH sequence can accurately determine the extent of the necrotic area after RF ablation.