Three-dimensional monitoring of small temperature changes for therapeutic hyperthermia using MR

Radiofrequency hyperthermia of deep-seated pelvic tumors requires noninvasi ve monitoring of temperature distributions in patients. Methods of MR therm ography were reported to be a promising tool in solving this problem. Howev er, to be truly useful for monitoring hyperthermia treatments, MR thermogra phy should be able to cover the entire pelvis in acquisition times no longe r than for a breath-hold (less than or equal to 15 seconds) and to resolve small temperature differences (<1 degrees C). Three methods exploiting the temperature dependence of spin-lattice relaxation time (T1), of self-diffus ion coefficient (D), and of chemical shift of proton resonance frequency (P RF) were applied in phantom experiments: the pulse sequences were the T1-we ighted gradient echo, the pulsed diffusion gradient spin echo made faster t hrough the keyhole technique, and the gradient echo with the phase reconstr uction, respectively, The high planar resolution wag compromised, and inste ad, coarse and mole isotropic voxels were used, Experiments were performed in two consecutive steps, thus imitating a possible scenario for monitoring hyperthermia, In the first step, calibration curves were recorded, which w ere then used in the second step to obtain maps of temperature changes. The results show a clear superiority of the PRF method, followed by the D and the T1 methods, The uncertainty of temperature changes predicted both from calibration curves and from maps was less than 1 degrees C only with the PR F and the D-based methods.