Dual energy quantitative computed tomography in the analysis of vertebral trabecular bone compositio

Single energy quantitative computed tomography (QCT) is an established technique for the estimation of vertebral trabecular mineral content, a measurement of clinical value in the management of metabolic bone disease. This measurement is precise (reproducible) but its accuracy is influenced by the presence of other tissue in the region of interest, particularly fat, which has a negative CT attenuation value and thus results in reduction of the measured mineral content. Scanning the same region of trabecular bone at a different X-ray beam energy allows recalculation of the mineral content with correction for the effect of fat as relative attenuations of the various components of trabecular bone change with X-ray energy. Several methods of analysis of such dual energy CT data have been described. They are all less precise but experimentally more accurate than single energy Qcr. Some of the dual energy methods also allow an estimate of vertebral trabecular fat content to be derived. This thesis compares the accuracy and precision of the described post-processing methods of dual energy quantitative computed tomography for both fat and mineral estimation in vivo and in vitro. Investigation of the effects of temperature on QCT by in vitro experiments demonstrated that scanning vertebral specimens at room temperature underestimates the influence of fat on SEQCT mineral densitometry with serious consequences for the interpretation of all published in vitro studies to date. The author develops another DEQCT method that can be applied in vivo in the Manchester Medical School Department of Diagnostic Radiology. All these methods have then been applied to a review and re-analysis of single and dual energy quantitative computed tomographic examinations in patients with a variety of conditions which may affect trabecular bone composition. Increased marrow fat con-tent as well as reduced mineral density was demonstrated in patients with Cushing's disease and in osteoporosis, whilst replacement of marrow fat was evident in metastatic breast carcinoma. Widely varying marrow composition was demonstrated in patents with osteomalacia. The results of these analyses and comparisons with other methods are described and the clinical role of DEQCT for the analysis of vertebral trabecular bone composition is discussed.