Feasibility of abdomino‐pelvic T1‐weighted real‐time thermal mapping of laser ablation

PURPOSE: To prove the hypothesis that T1-weighted (T1W) thermal mapping is reliable and achievable in magnetic resonance (MR)-guided laser tumor ablation. MATERIALS AND METHODS: Near real-time gray and color-scale T1W thermal maps in 111 MR-guided laser thermal ablations (LTA) of liver, kidney, and uterine tumors were studied. After laser fiber placement, near real-time gray and color-scale thermal maps were produced. Previous work showed T1 signal is inversely proportional to temperature below 55 degrees C (the point of irreversible necrosis). RESULTS: Thermal mapping was successful in 84% of uterine, 74% of hepatic, and 20% of renal ablations. For hepatic and uterine tumors, size and conspicuity of thermal lesions were significantly greater on subtracted colorized images rather than gray-scale raw image mapping (P = 0.001, paired Student's t-test). Patient movement (N = 24), fiber charring N = 2), magnetic field distortion, and reconstruction errors (N = 2) caused mapping failure. For both renal and hepatic tumors, comparison of near real-time T1W colorized thermal map and follow up gadolinium-enhanced MR imaging revealed moderate correlation (Pearson correlation coefficient of 0.55 and 0.5, respectively). CONCLUSION: In hepatic, renal, and uterine thermal maps, the color scale produced significantly greater sized lesions with significantly greater conspicuity than the gray scale. T1W thermal mapping was reliable and successfully achieved in 73.7% of procedures, and predicted the ablated area of the tumor moderately well.