Magnetic Resonance Temperature Imaging

Continuous, real-time 3D temperature mapping during a hyperthermic procedure may provide enhanced safety by visualizing temperature maps in and around the treated region, improved efficiency by adapting local energy deposition with feedback coupling algorithms, and therapy endpoints based on the accumulated thermal dose. Noninvasive mapping of temperature changes can be achieved with MRI, and may be based on temperature dependent MRI parameters. The excellent linearity of the temperature dependency of the proton resonance frequency (PRF) and its near-independence with respect to tissue type make the PRF-based methods the preferred choice for many applications, in particular at mid to highfield strength (≥ 0.5 T). The PRF methods employ RF-spoiled gradient echo imaging methods, and incorporate fat suppression techniques for most organs. A standard deviation of less than 1 o C, for a temporal resolution below 1 s and a spatial resolution of about 2 mm, is feasible for immobile tissues. Special attention is paid to methods for reduction of artifacts in MR temperature mapping caused by intra-scan and inter-scan motion, and motion and temperature-induced susceptibility effects in mobile tissues. Real-time image processing and visualization techniques, together with accelerated MRI acquisition techniques, are described because of their primary importance for real-time, image guided, therapy guidance