| Περίληψη: | <p>The potential deleterious effects of ionising radiation continue to be highlighted, with radiation reduction largely consisting of low dose techniques rather than a shift to non-ionising methods. The craniofacial region is a key anatomical area for radiation protection in view of the radiosensitive lens and thyroid gland. CT scanning is routinely employed to image this region in view of its superior imaging of bone and ability to create 3D rendered images and anatomical models for diagnosis and surgical planning. Standard MRI sequences make 3D rendering of bone a challenging problem. The objectives of the thesis were to explore the potential of MRI as an alternative to CT in three key patient groups: children with premature fusion of the cranial sutures (craniosynostosis), adolescents with facial disproportion, and adults with malignancy of the facial skeleton. Investigation was undertaken with routine MRI sequences, and a new low flip-angle gradient echo sequence "Black Bone."</p> <p>Overall, the potential of "Black Bone" far exceeded that of routine MRI sequences. In children with craniosynostosis, the cranial sutures were clearly delineated on "Black Bone" with accurate distinction between normal and prematurely fused sutures. In adolescents with facial disproportion "Black Bone" offered a reliable method of 2D-cephalometric assessment with potential for development of 3D cephalometry. In adults with malignancy of the craniofacial skeleton the "Black Bone" sequence was useful in detecting bony erosion and tumours contained within the facial skeleton. However it was of limited value in tumour volume measurements where the tumour involved surrounding soft tissues, and routine sequences offered a reliable solution. A positive correlation was seen with tumour volume and clinical outcome, surpassing the accuracy of the current TNM staging system.</p> <p>The clear soft-tissue-bone boundary of the "Black Bone" sequence was successfully utilised for the first time to produce 3D rendered images and anatomical models of the craniofacial skeleton from MRI datasets. This novel application demonstrated comparable accuracy of "Black Bone" and CT rendered datasets.</p> <p>This work has made a significant contribution to radiation protection and is likely to change clinical practice in the near future.</p>
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