The purpose of the study was to develop a simulation approach for laser-induced thermotherapy (LITT) that is based on mathematical models for radiation transport, heat transport, and tissue damage. The LITT ablation was applied to ex vivo pig liver tissue. Experiments were repeated with different laser powers, i.e., 22-34 W, and flow rates of the cooling water in the applicator system, i.e., 47-92 ml/min. During the procedure, the temperature was measured in the liver sample at different distances to the applicator as well as in the cooling circuit using a fiber optic thermometer. For validation, the simulation results were compared with the results of the laser ablation experiments in the ex vivo pig liver samples. The simulated and measured temperature curves presented a relatively good agreement. The Bland-Altman plot showed an average of temperature differences of -0.13 C and 95%-limits-of-agreement of ±7.11C. The standard deviation amounted to ±3.63 C. The accuracy of the developed simulation is comparable with the accuracy of the MR thermometry reported in other clinical studies. The simulation showed a significant potential for the application in treatment planning.
To assess the benefit of routinely used three-dimensional 1H-spectroscopy of the prostate combined with magnetic resonance imaging in patients with elevated prostate-specific antigen (PSA) levels and negative or no previous prostate biopsies. Fifty-four patients were examined with our combined imaging protocol, which consisted of transversal, coronal and sagittal T2-weighted fast spin echo sequences. For spectroscopy, we used a three-dimensional chemical shift imaging spin echo (3D-CSI-SE) sequence. The study population consisted of patients with elevated PSA levels and histologically proven prostate carcinoma and patients with elevated PSA levels and negative or no previous prostate biopsies. Examination time was 31 min, a time feasible for routine use. Eighty-eight tumour voxels and 67 control voxels of 27 patients with histologically proven prostate carcinoma were analysed. Ratios of (choline + creatine)/citrate [(Cho + Crea)/Cit] below 0.6 were classified as normal and above 0.6 as pathological. Applying this classification to 20 patients with tumour-suspicious lesions of the prostate and negative or no previous prostate biopsies, we could obtain a sensitivity and specificity for tumour detection of 100% and 69%, respectively. Our combined imaging protocol is feasible for routine use and can add valuable information for the diagnostic management of patients with negative or no previous prostate biopsies.
The purpose of this study was to evaluate magnetic resonance (MR) temperature imaging of the laser-induced thermotherapy (LITT) comparing the proton resonance frequency (PRF) and T 1 thermometry methods. LITT was applied to a liver-mimicking acrylamide gel phantom. Temperature rise up to 70 °C was measured using a MR-compatible fiber-optic thermometer. MR imaging was performed by a 1.5-T scanner utilizing fast gradient echo sequences including a segmented echo planar imaging (seg-EPI) sequence for PRF and the following sequences for T 1 method: fast low-angle shot (FLASH), inversion recovery turbo flash (IRTF), saturation recovery turbo flash (SRTF), and true fast imaging (TRUFI). Temperature-induced change of the pixel values in circular regions of interest, selected on images under the temperature probe tip, was recorded. For each sequence, a calibration constant could be determined to be -0.0088 ± 0.0002 ppm °C(-1) (EPI), -1.15 ± 0.03 °C(-1) (FLASH), -1.49 ± 0.03 °C(-1) (IRTF), -1.21 ± 0.03 °C(-1) (SRTF), and -2.52 ± 0.12 °C(-1) (TRUFI). These constants were evaluated in further LITT experiments in phantom comparing the calculated temperatures with the fiber optic-measured ones; temperature precisions of 0.60 °C (EPI), 0.81 °C (FLASH), 1.85 °C (IRTF), 1.95 °C (SRTF), and 3.36 °C (TRUFI) were obtained. Furthermore, performing the Bland-Altman analysis, temperature accuracy was determined to be 0.23 °C (EPI), 0.31 °C (FLASH), 1.66 °C (IRTF), 1.19 °C (SRTF), and 3.20 °C (TRUFI). In conclusion, the seg-EPI sequence was found to be more convenient for MR temperature imaging of LITT due to its relatively high precision and accuracy. Among the T 1 method sequences, FLASH showed the highest accuracy and robustness.
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