Monitoring and visualization techniques for MR-guided laser ablations in an open MR system

Our purpose was to develop temperature-sensitive MR sequences and image-pro cessing techniques to assess their potential of monitoring interstitial las er therapy (ILT) in brain tumors (n = 3) and liver tumors (n = 7). ILT last ed 2 to 26 minutes, whereas images from T1-weighted fast-spin-echo (FSE) or spoiled gradient-recalled (SPGR) sequences were acquired within 5 to 13 se conds. Pixel subtraction and visualization of T1-weighted images or optical now computation was done within less than 110 msec, Alternating phase-mapp ing of real and imaginary components of SPGR sequences was performed within 220 msec. Pixel subtraction of T1-weighted images identified thermal chang es in liver and brain tumors but could not evaluate the temperature values as chemical shift-based imaging, which was, however, more affected by susce ptibility effects and motion, Optical now computation displayed the predict ed course of thermal changes and revealed that the rate of heat deposition can be anisotropic, which may be related to heterogeneous tumor structure a nd/or vascularization.