gms | German Medical Science

Objectives: Osteoporosis is a silent disease that is often diagnosed only after a fracture has already occurred. This emphasizes the need for earlier diagnosis. Quantitative Computer tomography (QCT) as a diagnostic tool to measure bone mineral density (BMD) is approved for native computer tomography (CT). CT-scans such as for polytrauma are often performed under contrast agent administration. The aim of this study was to investigate whether contrast enhanced (CE) CT can also be used for routine BMD-measurement. Measurements of non-enhanced (NE) CT used so far for this purpose were compared with the results of CE-CT for the spine and proximal femur.

Methods: Using the search terms polytrauma and CTA-hemorrhage, patients from a national level-1 trauma center were identified who had received both NE- and CE-CT in a maximum interval of 6 months. BMD measurements in the spine region were performed with QCT for NE and CE scans. Corresponding measurements were performed in the hip region to evaluate possible location-specific differences. Monthly asynchronous calibration was performed on all CT-scanners. Additional parameters such as age, weight and height were collected.

Results and conclusion: 130 patients were included, 60 (46.2%) with spine only, 3 (2.3%) with hip only and 67 (51,5%) with both hip and spine. BMD-measurements differed significantly between NE and CE scans, 122.9± 48.2 mg/cm³ (NE) vs. 143.8± 46.4 mg/cm³ (CE) for spine and 123.2 ± 37.5 mg/cm³ (NE) vs. 126 ± 36.7 mg/cm³ (CE) for hip.

The mean effect of contrast media differed between spine (19.4 mg/cm³) and hip (2.8 mg/cm³) indicating that there is a location-specific effect of contrast media. We determined location-specific conversion factors which allow to calculate the true BMD-values. The additional parameter BMI showed negative correlation with a lower effect of the contrast agent at higher BMI.

Results show that CE scans cannot be used directly for BMD-diagnostics because contrast media significantly alters the BMD. We established location specific conversion factors, which are likely to depend on additional parameters such as BMI of the patient. Conversion factors can be used to calculate reliable volumetric BMD measurements for both the spine and hip from routine CT datasets.