Intravenous contrast injection significantly affects bone mineral density measured on CT

Objective The objective is to evaluate the effect of intravenous contrast media on bone mineral density (BMD) assessment by comparing unenhanced and contrast-enhanced computed tomography (CT) examinations performed for other indications. Methods One hundred and fifty-two patients (99 without and 53 with malignant neoplasm) who underwent both unenhanced and two contrast-enhanced (arterial and portal venous phase) abdominal CT examinations in a single session between June 2011 and July 2013 were included. BMD was evaluated on the three examinations as CT-attenuation values in Hounsfield Units (HU) in the first lumbar vertebra (L1). Results CT-attenuation values were significantly higher in both contrast-enhanced phases, compared to the unenhanced phase (p<0.01). In patients without malignancies, mean +/- standard deviation (SD) HU-values increased from 128.8 +/- 48.6 HU for the unenhanced phase to 142.3 +/- 47.2 HU for the arterial phase and 147.0 +/- 47.4 HU for the portal phase (p<0.01). In patients with malignancies, HU-values increased from 112.1 +/- 38.1 HU to 126.2 +/- 38.4 HU and 130.1 +/- 37.3 HU (p<0.02), respectively. With different thresholds to define osteoporosis, measurements in the arterial and portal phase resulted in 7-25 % false negatives. Conclusions Our study showed that intravenous contrast injection substantially affects BMD-assessment on CT and taking this into account may improve routine assessment of low BMD in nonquantitative CT.