A fast referenceless MR thermometry technique

Referenceless proton resonance frequency (PRF) shift thermometry is robust to B₀ drift and inter-scan tissue displacement in temperature change measurement during minimally invasive thermotherapy procedures such as High Intensity Focused Ultrasound (HIFU). In this method, the baseline phase of the heated region is extrapolated from unheated region by a polynomial model. The procedure would involve the time-consuming phase unwrapping procedure necessary for polynomial modeling. We propose here a novel method for referenceless PRF without the need for phase unwrapping. The method fits the spatial derivative of phase image to the polynomial model to avoid phase unwrapping. The baseline phase of heated region is then numerically integrated from the predicted phase derivative image based on the polynomial model. Our experiment demonstrated that the new method improved computational efficiency by 2 to 4 times with slightly better accuracy to the original referenceless thermometry. The speed improvement would facilitate the application of the technique to multi-slice and 3D near-real-time MR thermometry.