Automatic control of hyperthermic therapy based on real-time Fourier analysis of MR temperature maps

Local hyperthermia is increasingly being used for therapeutic purposes, such as tumor ablation. Heat conduction and energy absorption in vivo during the hyperthermic procedure are largely unknown, thus making feedback temperature control highly desirable. Here, a general method for temperature control based on Fourier transformation (FT) of the bio-heat equation is presented, taking into account heat diffusion (D) and energy absorption (a) together with temperature distribution derived from rapid, continuous MR temperature mapping. The main advantages of the new method are: 1) the spatial distribution of heat deposition and conduction over the full region of interest (ROI) is taken into account, and 2) the high speed resulting from the use of fast FT (FFT) of temperature maps allows rapid feedback coupling. Initial tests based on MRI-guided focused ultrasound (FUS) demonstrated that high-quality temperature regulation can be obtained even for erroneous values of D and a., so long as their relative error remained in the same range. Performance of the automated control procedure was validated ex vivo and in vivo on rabbit thigh using moderate FUS heating. During the procedure, the standard deviation (SD) of the temperature remained in the range of temperature noise obtained by MRI, indicative of the performance of the regulation algorithm.