Non-invasive temperature mapping using MRI:: Comparison of two methods based on chemical shift and T1-relaxation

Purpose: To implement and evaluate the accuracy of non-invasive temperature mapping using MRI methods based on the chemical shift (CS) and T-1 relaxation in media of various heterogeneity during focal (laser) and external thermal energy deposition. Materials and Methods: All measurements mere performed on a 1.5 T superconducting clinical scanner using the temperature dependence of the water proton chemical shift and the T-1 relaxation time, Homogeneous gel and heterogeneous muscle phantoms were heated focally with a fiberoptic laser probe and externally of varying degree ex vivo by water circulating in a temperature range of 20-50 degrees C. Magnetic resonance imaging data were compared to simultaneously recorded fiberoptic temperature readings. Results: Both methods provided accurate results in homogeneous media (turkey) with better accuracy for the chemical shift method (CS: +/-1.5 degrees C, T-1: +/-2.0 degrees C:). Ln gel, the accuracy with the CS method was +/-0.6 degrees C. The accuracy decreased in heterogeneous media containing fat (T-1: +/-3.5 degrees C, CS: +5 degrees C). In focal heating of turkey muscle, the accuracy was within 1.5 degrees C with the T-1 method. Conclusion: Temperature monitoring with the chemical shift provides better results in homogeneous media containing no fat, In fat tissue, the temperature calculation proved to be difficult. (C) 1998 Elsevier Science Inc.