Purpose: To implement and evaluate the accuracy of non-invasive temperature mapping using MRI methods based on the chemical shift (CS) and T1 relaxation in media of various heterogeneity during focal (laser) and external thermal energy deposition.
Materials and methods: All measurements were performed on a 1.5 T superconducting clinical scanner using the temperature dependence of the water proton chemical shift and the T1 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, T1:+/-2.0 degrees C). In gel, the accuracy with the CS method was +/-0.6 degrees C. The accuracy decreased in heterogeneous media containing fat (T1:+/-3.5 degrees C, CS: +5 degrees C). In focal heating of turkey muscle, the accuracy was within 1.5 degrees C with the T1 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.