On T1W images, the probe was well visible with an adequate artifact size. Immediately after RF, the MR images showed a hypointense lesion around the probe tip which became isointense within 15 minutes on subsequent images. The size of the macroscopic thermal lesion corresponded to the size of the zone of signal loss (Fig. 2).

All eight treatment sessions were well tolerated, no adverse effects were noted and discharge from hospital was possible after 24 hours in all instances. The time required for probe placement was approximately 30-50 minutes per lesion and total procedural time was 60-120 minutes per session. The interactive iPath 200® device proved to be particularly helpful in situations that required an angulated approach. Documentation of the probe position prior to RF application was always feasible (Fig.4). In all liver metastases, contrast-enhanced T1W images immediately after treatment showed a lack of contrast medium uptake in a region exceeding the volume of the initial tumor nodule (Fig 4C). On T2W images the metastases which had displayed a hyperintense signal prior to treatment, became isointense with liver tissue (Fig. 4D). The three hypervascular HCC lesions showed lack of enhancement on both post-procedural MRI and CT. Comparison between lesion size before and after RF treatment and outcome is given in table 1.