Background Osteoporosis is a prevalent but underdiagnosed condition. Objective To evaluate computed tomography (CT)-derived bone mineral density (BMD) assessment compared with dual-energy x-ray absorptiometry (DXA) measures for identifying osteoporosis by using CT scans performed for other clinical indications. Design Cross-sectional study. Setting Single academic health center. Patients 1867 adults undergoing CT and DXA (n = 2067 pairs) within a 6-month period over 10 years. Measurements CT-attenuation values (in Hounsfield units [HU]) of trabecular bone between the T12 and L5 vertebral levels, with an emphasis on L1 measures (study test); DXA BMD measures (reference standard). Sagittal CT images assessed for moderate-to-severe vertebral fractures. Results CT-attenuation values were significantly lower at all vertebral levels for patients with DXA-defined osteoporosis (P < 0.001). An L1 CT-attenuation threshold of 160 HU or less was 90% sensitive and a threshold of 110 HU was more than 90% specific for distinguishing osteoporosis from osteopenia and normal BMD. Positive predictive values for osteoporosis were 68% or greater at L1 CT-attenuation thresholds less than 100 HU; negative predictive values were 99% at thresholds greater than 200 HU. Among 119 patients with at least 1 moderate-to-severe vertebral fracture, 62 (52.1%) had nonosteoporotic T-scores (DXA false-negative results), and most (97%) had L1 or mean T12 to L5 vertebral attenuation of 145 HU or less. Similar performance was seen at all vertebral levels. Intravenous contrast did not affect CT performance. Limitation The potential benefits and costs of using the various CT-attenuation thresholds identified were not formally assessed. Conclusion Abdominal CT images obtained for other reasons that include the lumbar spine can be used to identify patients with osteoporosis or normal BMD without additional radiation exposure or cost. Primary Funding Source National Institutes of Health.

Purpose To evaluate the utility of lumbar spine attenuation measurement for bone mineral density (BMD) assessment at screening CT colonography (CTC), using central dual-energy x-ray absorptiometry (DXA) as the reference standard. Material and Methods 252 adults (240 women, 12 men; mean age, 58.9 years) underwent CTC screening and central DXA BMD measurement within 2 months (mean interval, 25.0 days). The lowest DXA T-score between the spine and hip served as the reference standard, with low BMD defined per WHO as osteoporosis (DXA T-score ≤-2.5) or osteopenia (DXA T-score between −1.0 and −2.4). Both phantomless QCT and simple non-angled ROI MDCT attenuation measurements were applied to T12-L5 levels. Ability to predict osteoporosis and low BMD (osteoporosis or osteopenia) by DXA was assessed. Results A BMD cut-off of 90 mg/cc at phantomless QCT yielded 100% sensitivity for osteoporosis (29/29) and specificity of 63.8% (143/224); 87.2% (96/110) below this threshold had low BMD and 49.6% (69/139) above this threshold had normal BMD at DXA. At L1, a trabecular ROI attenuation cut-off of 160 HU was 100% sensitive for osteoporosis (29/29), with a specificity of 46.4% (104/224); 83.9% (125/149) below this threshold had low BMD and 57.5% (59/103) above had normal BMD at DXA. ROI performance was similar at all individual T12-L5 levels. At ROC analysis, AUC for osteoporosis was 0.888 for phantomless QCT (95% CI: 0.780–0.946) and ranged from 0.825–0.853 using trabecular ROIs at single lumbar levels (0.864 [0.752–0.930] at multivariate analysis). Supine-prone reproducibility was better with simple ROI method compared with QCT. Conclusion Both phantomless QCT and simple ROI attenuation measurements of the lumbar spine are effective for BMD screening at CTC, with high sensitivity for osteoporosis as defined by the DXA T-score.

Assessment of liver attenuation by use of unenhanced CT represents an objective and noninvasive means for detection of asymptomatic hepatic steatosis, whereas clinical risk factor assessment is unreliable. Further longitudinal investigation is needed to determine the most appropriate attenuation threshold and the risk for disease progression to steatohepatitis and cirrhosis.

We identified a high incidence of acute kidney injury among control subjects undergoing unenhanced CT. The incidence of creatinine elevation in this group was statistically similar to that in the isoosmolar contrast medium group for all baseline creatinine values and all stages of chronic kidney disease. These findings suggest that the additional risk of acute kidney injury accompanying administration of contrast medium (contrast-induced nephrotoxicity) may be overstated and that much of the creatinine elevation in these patients is attributable to background fluctuation, underlying disease, or treatment.