Correlation between CT attenuation value and iodine concentration in vitro: discrepancy between gemstone spectral imaging on single-source dual-energy CT and traditional polychromatic X-ray imaging

Abstract

Introduction: To assess the relation between CT attenuation value and iodine concentration in vitro, using gemstone spectral imaging (GSI) with single-source dual-energy CT and traditional polychromatic X-ray imaging (TPXI), respectively.

Methods: A polypropylene phantom with eight test tubes in which iodine concentrations of solution were 0.4, 0.7, 2, 5, 10, 20, 30 and 50 mg/mL underwent GSI and traditional polychromatic X-ray scans (80, 100, 120 and 140 kV(p)), using single-source dual-energy spectral CT (Discovery CT750HD; GE Healthcare Technologies, Milwaukee, WI, USA) at the same tube speed of 0.8 s/rotation. All spectral imaging data were analysed with GSI viewer to obtain monochromatic images (50-140 keV, interval of 10 keV). Computed tomography attenuation values of iodine solution were measured with the same size of regions of interest and at the exact same level for both monochromatic and polychromatic images. The relation between CT attenuation value and iodine concentration was examined.

Results: A linear correlation was found between CT attenuation value and iodine concentration for both monochromatic and polychromatic images. Moreover, the fitting coefficients for CT attenuation values and iodine concentrations were closer to one with GSI (r(2) = 0.99824-0.99996) than that with TPXI (r(2) = 0.99640-0.99736).

Conclusions: Owing to the better correlation coefficients between CT attenuation value and iodine concentration, GSI may be a preferred method for quantitative measurement compared with TPXI.