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The aim of the thesis was to compare the methods of CR and LDCT for musculoskeletal imaging of the pelvis, hip and thoracic and lumbar spine to investigate if LDCT can achieve similar or higher diagnostic quality compared to CR, with an equal level of radiation exposure. The comparison focused on image quality, visibility and radiation dose, with the addition of diagnostic findings.

In paper I 21 patients, who had undergone open reduction and internal fixation of pelvic fracture, were examined with CR and LDCT. Hardware positioning, fracture reduction, image quality and radiation dose was noted. In paper II a phantom with hip prosthesis and tantalum markers was scanned with 14 different CT protocols. The image sets were assessed regarding image quality, robustness of numerical data for migration and radiation dose. The protocol with highest overall score and an estimated radiation dose < 1mSv was applied to a pilot patient. In paper III and IV, 63 and 84 patients respectively were examined with routine CR and LDCT with a study protocol. Technical and diagnostic image quality and visibility was assessed. Diagnostic findings were noted. An AI software was used for visibility of vertebrae and fracture detection. Radiation dose was calculated.

LDCT had a significantly higher image quality than CR in the post-operative pelvis and the thoracic and lumbar spine, but also significantly higher radiation doses. LDCT is more reliable in assessing hardware and fracture reduction in the pelvis. LDCT can be used to perform precise migration measurements in patients with hip prosthesis with a radiation dose comparable to CR. More fractures were detected with LDCT than CR in the thoracic spine but not in the lumbar. There was no difference in detected compression fractures in LDCT between AI and radiologists in either thoracic or lumbar spine.

The findings of this thesis indicates that it is possible to examine the pelvis, hips with prosthesis, and thoracic and lumbar spine with LDCT and get as good or better diagnostic information with higher image quality than CR. More work is needed to further reduce radiation dose.