 Real–time US is the preferred method to place the RF probe because of its real-time capabilities, speed, low cost, and overall convenience5. In some cases, however, lesion conspicuity with US may be insufficient or artifacts may preclude an adequate percutaneous access. Ablation of large or asymmetrical lesions may require repositioning of the probe in different areas, which is often hampered by strong cavitation artifacts. Our rationale for investigating MRI as a tool for RF guidance in selected patients was related to several inherent advantages of MRI, namely, improved lesion conspicuity, the possibility to place the probe interactively and the potential to display temperature–induced changes in tissue. It has been shown that MRI, combined with Mn-DPDP, achieves equal or superior lesion conspicuity as CT but offers a much larger temporal window for probe placement than dynamic CT in both HCC and colorectal liver metastases6. This appears to hold true also at low field7. Open-magnet MR imaging at low field strength offers adequate access for probe placement. On the other hand, the procedure is technically quite complex, and repetitive image acquisition is necessary during probe placement. In summary, our preliminary experience suggests that the above-described RF probe can be used effectively and safely in an open-magnet MR system. Several improvements in hardware and software are still required, including the quality of images acquired on a single breathhold.
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