Thermoablative Treatments for Malignant Liver Lesions: 10-Year Experience of MRI Appearances of Treatment Response

OBJECTIVE. The objective of our study was to describe our 10-year experience using MRI to evaluate response to local thermoablative interventions in the treatment of malignant liver lesions. MATERIALS AND METHODS. This retrospective study was conducted from 1998 to 2008. MRI studies were performed at 1.5 and 3 T and were acquired < 4, 4-9, and > 9 months after radiofrequency ablation (RFA), cryoablation, and microwave ablation. MR features were evaluated on the basis of signal intensity on unenhanced T1-weighted images and the presence of ill-defined perilesional enhancement, well-defined lesional enhancement, or washout on contrast-enhanced images. Imaging features were evaluated with all interventional modalities together and separately. RESULTS. The study population was composed of 135 men and 36 women (203 ablated lesions) with a mean age of 65 years (range, 39-78 years). When the data for all treatment methods were combined, well-defined lesional enhancement and washout were significant findings among the resolved and unresolved outcome groups regardless of follow-up time category. After RFA, ablated areas had a tendency to show high signal intensity on T1 images, whereas low signal was seen after cryoablation and a hyperintense rim was seen after microwave ablation. Washout was only depicted 9 months after cryoablation but was seen in 12% of lesions < 4 months after RFA. No difference was appreciated on ill-defined perilesional enhancement with all methods combined or separately. CONCLUSION. MRI findings after ablation are dependent on the treatment modality and the length of time between the procedure and follow-up examination.