AbstractsMedical & Health Science

This work studied the conversion of the magnetic resonance images to synthetic heterogeneous computed tomography (CT) images, so-called pseudo-CT images. The study focused on updating and modifying a previously introduced conversion technique. Ultimate objective of this study was to verify the technique after a hardware and software update of the MR scanner. This included adjustments of the image conversion algorithms and integration of these into a medical image processing software. Additionally, this work aimed to use automatic bone segmentation atlas with the technique. The updated technique was verified for prostate cancer patients. This work aimed also to evaluate possibilities to adopt the technique for other patient groups and with different MR scanner. The evaluation included measurement for geometric accuracy in MR images. Average local difference in Hounsfield units (HU) between pseudo-CT and actual CT images for soft- and bony tissues were -1±13 HU and -10±139 HU, respectively. Measurement points in soft tissue had coverage of 89 % with smaller absolute error than 20 HUs. In bony tissue average of 88 % of the measurement points were within 200 HU error margin. The dose difference between pseudo-CT and actual CT images was -0.4 % ± 0.2%. Dose difference in PTV for automated bone contouring against user corrected bone volumes was 0.1 % ± 0.1 %. The calculated dose in heterogeneous pseudo-CT was shown statistically significantly (p = 0.0014) more accurate compared to that in simplified pseudo-CT. The geometric error was within 1.1 mm for distances shorter than 20 cm from isocenter with two scanners. Preliminary pseudo-CT images were created with modified conversion algorithms for thigh and abdomen. Magnetic resonance imaging- based radiation therapy treatment planning provides reliable method for radiotherapy treatment in pelvic areas reaching the requirements in patient care. This study showed that the MR image conversion technique can be adjusted in case of updates in MR platform. The examinations suggested also that it seems doable to adopt the MR image conversion technique to different body parts and with different MR scanners.