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Figure 11b.   MR imaging-guided laser ablation. (a) Photograph shows a patient positioned in an MR imaging unit (0.2-T Viva [Siemens Medical Systems, Iselin, NJ]) with the radiologist performing the procedure. (b) Sagittal MR image obtained after administration of ferumoxide contrast material shows the high-signal-intensity tumor (arrow) into which two needles (arrowheads) have been inserted.