MRI THERMOMETRY IN PHANTOMS BY USE OF THE PROTON-RESONANCE FREQUENCY-SHIFT METHOD - APPLICATION TO INTERSTITIAL LASER THERMOTHERAPY

In this work the temperature dependence of the proton resonance freque ncy was assessed in agarose gel with a high melting temperature (95 de grees C) and in porcine liver in vitro at temperatures relevant to the rmotherapy (25-80 degrees C). Furthermore, an optically tissue-like ag arose gel phantom was developed and evaluated for use in MRI. The phan tom was used to visualize temperature distributions from a diffusing l aser fibre by means of the proton resonance frequency shift method. An approximately linear relationship (0.0085 ppm degrees C-1) between pr oton resonance frequency shift and temperature change was found for ag arose gel, whereas deviations from a linear relationship were observed for porcine liver. The optically tissue-like agarose gel allowed reli able MRI temperature monitoring, and the MR relaxation times (T-1 and T-2) and the optical properties were found to be independently alterab le. Temperature distributions around a diffusing laser fibre, during i rradiation and subsequent cooling, were assessed with high spatial res olution (voxel size = 4.3 mm(3)) and with random uncertainties ranging from 0.3 degrees C to 1.4 degrees C (1 SD) with a 40 s scan time.