Babak Bazrafshan MS, Presenter: Nothing to Disclose

Frank Hübner MS, Abstract Co-Author: Nothing to Disclose

Christina Larson MD, Abstract Co-Author: Nothing to Disclose

Vitali Vogel, Abstract Co-Author: Nothing to Disclose

Werner Mäntele, Abstract Co-Author: Nothing to Disclose

Thomas Josef Vogl MD, Abstract Co-Author: Nothing to Disclose

To perform real-time MRI-based thermometry during tumor thermal ablation, PRF method with an EPI sequence is preferred due to its acceptable accuracy. Among the T1-weighted sequences, FLASH is preferable as the most robust and accurate sequence.

Tumor thermal ablation methods, among them Laser-induced Thermotherapy (LITT) and Radiofrequency Ablation (RFA), are nowadays widely in clinical use. In these methods, tumor is locally heated up to approximately 70 °C ensuring death of tumor cells. At the same time, surrounding healthy tissue should be protected. Therefore, a real-time temperature mapping for temperature controlling during the therapy is desirable.

Fast Magnetic Resonance Imaging (MRI) sequences were evaluated for both Proton Resonance Frequency (PRF) and T1 thermometry methods. MRI-guided LITT was applied to pig liver and gel phantom. Simultaneously, temperature was measured using a fluoroptic thermometer and MR imaging was performed utilizing an Echo Planar Imaging (EPI) sequence for PRF and the following sequences for T1 method: Fast Low Angle Shot (FLASH), Inversion Recovery Turbo FLASH (IRTF), Saturation Recovery Turbo FLASH (SRTF) and True Fast Imaging (TRUFI). Plotting MRI signal intensity obtained from magnitude images against measured temperature determined a temperature coefficient for each T1-weighted sequence. To identify the PRF temperature coefficient, phase values gained from phase images were plotted against temperature. Finally, the temperature coefficients were examined in further LITT experiments.

Temperature coefficients were determined for FLASH, IRTF, SRTF and TRUFI sequences as follows: 0.49, 0.52, 0.26 and 0.24 %/°C, respectively. Regarding linearity of data points, analyses resulted in coefficients of determination of 0.996 (FLASH), 0.990 (IRTF), 0.979 (SRTF) and 0.975 (TRUFI). For EPI sequence, an excellent linear correlation of phase values and measured temperatures was detected which led to a temperature coefficient of 0.011 ppm/°C. Concerning temperature coefficient validation, the results are still being processed, with initial analysis showing measured and MRI-based temperatures agreement for EPI sequence.

Bazrafshan, B, Hübner, F, Larson, C, Vogel, V, Mäntele, W, Vogl, T, Noninvasive Magnetic Resonance Imaging-based Thermometry: An ex Vivo Study on Pig Liver and Gel Phantom.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9006786.html