The impact of imaging time and contrast agent dose on screening for osteoporosis with contrast-enhanced CT

Background Screening for osteoporosis with contrast-enhanced computed tomography (CT) is promising for identifying high-risk osteoporotic patients. Our aims were (1) to investigate the estimated volume bone mineral density (vBMD) change over time after contrast injection (CT perfusion imaging, CTPI); and (2) to examine the influence of contrast dose on vBMD. Methods Fifteen patients, aged 71 ± 9 years (mean ± standard deviation, range 55–86) underwent a CTPI examination (28 scans within 63 s) of the upper body followed (after a waiting time of 10 min) by a full 4-phase CT examination (4 scans within 4 min). The contrast dose for CTPI was 0.38–0.83 mL/kg, and for 4-phase CT was 0.87–1.29 mL/kg. Vertebrae L1–L3 were analysed totalling 43 vertebrae, using Mindways qCT Pro. Results After contrast injection, vBMD showed a near-horizontal line until 17.5 s (non-contrast phase), followed by a steep increase 17.5–41.5 s after contrast injection, i.e. , in the arterial phase, which plateaued 41.5 s after, i.e. , in the early venous phase. A higher contrast dose per kg yielded significantly higher vBMD increase in both the arterial and venous phase ( p < 0.003). Conclusions Both time from contrast administration and contrast dose per kg affected vBMD results. In arterial phase, the steepness of the curve makes vBMD estimation unsure. However, as values plateaued in the venous phase it might be possible to predict the correct vBMD values. Furthermore, contrast dose is a factor that needs to be adjusted for when using such a formula.