Purpose: To evaluate the feasibility and accuracy of monitoring radio-frequency (RF) ablation with an open-configuration, 0.5-T magnetic resonance (MR) imager.
Materials and methods: Thirty-six in vivo RF ablation experiments were performed in porcine paravertebral muscle (n = 24) and liver (n = 12). A 90 degrees C tip temperature was applied for 3-9 minutes. MR images were acquired after continuous or during intermittent RF application. Temperature changes were monitored as signal intensity and proton-frequency-shift (PFS) alterations in two T1-weighted gradient-echo sequences. An update image was obtained every 2.5 seconds (20/10 [repetition time msec/echo time [TE] msec]) or every 5.0 seconds (40/20). A color-coded subtraction technique enhanced the signal intensity and PFS changes. Macroscopic coagulation size was compared with MR image lesion size.
Results: The RF application mode had no significant effect on coagulation size in muscle or liver (P > .05). Twenty-two of 24 coagulative lesions in muscle and nine of 12 in liver were demonstrated with the PFS technique. Accuracy of lesion size determination depended on TE (TE = 20 msec, r = .95; TE = 10 msec, r = .78 [P < .01]). The T1-weighted technique depicted only six of 24 muscle and three of 12 liver lesion ablations. In the lesions depicted, macroscopic size was significantly underestimated (P < .001).
Conclusion: PFS MR monitoring of RF effects in liver and muscle is feasible and accurate. The PFS technique outperformed the T1-weighted technique.