The use of clinical CT for baseline bone density assessment

Purpose: Many patients having an abnormal initial bone densitometry study h ave had a previous abdominal/pelvic computed tomography (CT) for other clin ical reasons. This study evaluates if a nondedicated quantitative CT (QCT) abdominal/pelvic CT scan could be used as reliable baseline data for subseq uent dedicated bone density studies. Subjects and Methods: Twenty-sir: patients (13 men, 13 women) undergoing cl inically-indicated non-i.v. and i.v. contrast abdominal/pelvic CT had dedic ated QCT performed immediately following scans of the L1, L2, and L3 verteb ral bodies. QCT was then performed on all three scans. A repeated measures analysis of variance model was used to analyze the data in order to compare noncontrast clinical CT with QCT and noncontrast clinical with contrast cl inical CT. Results: The mean bone mineral density for the noncontrast clinical study w as 98.51 (mg/cc) versus 90.56 (mg/cc) for QCT (p = 0.0003; 95% confidence i nterval: 3.90 to 13.71). There was no significant difference (p = 0.085) be tween QCT performed from non-i.v. and i.v. contrast clinical CT scans. Conclusion: Bone densitometry can be performed from either non-i.v. or i.v. contrast clinical CT scans if a conversion factor is applied. This can be determined by utilizing a formula D-average = -7.83 + (0.99 x NCaverage), w here D-average and NCaverage are the abbreviations of "dedicated" and "nonc ontrast clinical" BMD averaged over vertebral bodies L1-L3, respectively.