Development of Non-Invasive Temperature Monitoring for RF Interstitial Hyperthermia Using an 0.2-T Open MR-Apparatus

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The technique of a non-invasive, real-time monitoring of the temperature change distribution has been one of the desired methods in performing hyperthermia treatment. The purpose of this study was to estimate the feasibility of temperature mapping using the phase mapping method during RF interstitial hyperthermia with a very low magnetic field(0.2-T) using phantoms and animals.The experiments were performed with a 0.2-T MR unit for interventional radiology using a head surface coil. Vegetable oil containers were used as comparative substance to observe the magnetic field deviation. The chemical shift change was measured with the phase mapping method using a gradient echo process. For RF interstitial hyperthermia, the power was supplied by a RF generator, which was driven at a frequency between 9.0 and 13.5 MHz, with the power of 2 to 7 W. (1)The spatial distribution of the magnetic field fluctuation : measured as phase difference distribution in an oil phantom. The spatial resolution was 1.56 x 1.56 x 5 mm3. (2)To obtain the temperature coefficient, 4.5mM CuSO4 solution phantoms were warmed up to 80℃ by microwave, then the phase difference images were processed during the cooling. The temperature coefficient obtained was -0.0096 ppm/℃. (3)Anesthetized and immobilized five New Zealand- White rabbits were used to confirm the efficacy of this system. The interstitial electrode was inserted into the rabbit's thigh. The RF power supply and temperature processing were performed alternately. The reconstructed temperature images were processed in 5 seconds.Feasibility of the temperature change distribution imaging with the 0.2-T open MR system with a quasi-real-time processing was demonstrated. The results shown in the present study suggest the possibility of clinical applications of such low-end field scanners to monitor the internal body temperature during RF interstitial hyperthermia.