Impact of intravenous CT contrast agents on internal calibration techniques to determine trabecular BMD of the lumbar spine

Objectives: Contrast agents are frequently administered in computed tomography (CT) scans used for opportunistic screening of osteoporosis. The objective of this study is to compare the impact of contrast-related bone mineral density (BMD) increase between phantom-based and internal CT calibration techniques.

Materials and methods: Phantom-based and internal CT calibration techniques were used to determine trabecular BMD in 93 existing clinical CT scans of the lumbar spine of 34 subjects, scanned before and after administration of contrast agents. BMD differences between native (Nat) and contrast-enhanced scans in arterial (Art) and portal venous (PV) phases were compared among calibration methods. Three pairs of internal reference materials were investigated: blood/air, subcutaneous adipose tissue (SAT)/air and muscle tissue/air.

Results: Contrast agents increased CT values of blood in the aorta and the inferior vena cava in the Art phase by 210 ± 99HU and 47 ± 35HU, respectively and in the PV phase by 110 ± 49HU and 73 ± 28HU, respectively. Effects on CT values of muscle and SAT were < 5HU in the Art phase and < 10HU in the PV phase. BMD obtained with phantom calibration increased significantly (p < 0.01) in Art and PV phases by 8.6 ± 14.7 mg/cm³ and 14.4 ± 16.3 mg/cm³, respectively. If SAT/air or muscle/air were used as internal reference materials, increases in internally calibrated BMD (<12 mg/cm³ in AT phase and < 17 mg/cm³ in PV phase) did not significantly differ (p > 0.1 for Art and PV phases) from increases of phantom-calibrated BMD.

Conclusions: Although CT values of internal reference materials increased following the administration of contrast, internal calibration was unable to mitigate the contrast-related BMD increases observed in phantom-based calibration.