Effect of tube potential and luminal contrast attenuation on atherosclerotic plaque attenuation by coronary CT angiography: In vivo comparison with intravascular ultrasound

Background: It has been shown that CT attenuation of noncalcified plaques depends on luminal contrast attenuation (LCA). Although tube potential (kilovolt [kV]) has been shown to exert influence on plaque attenuation through LCA as well as its direct effects, in-vivo studies have not investigated plaque attenuation at lower tube potentials less than 120 kV. We sought to evaluate the effect of kV and LCA on thresholds for lipid-rich and fibrous plaques as defined by intravascular ultrasound (IVUS). Methods: CT attenuation of IVUS-defined plaque components (lipid-rich, fibrous, and calcified plaques) were quantified in 52 consecutive patients with unstable angina, who had coronary CT angiography performed at 100 kV (n = 25) or 120 kV (n = 27) using kV-adjusted contrast protocol prior to IVUS. CT attenuation of plaque components was compared between the two groups. Results: LCA was similar in the 100-kV and 120-kV groups (417.6 +/- 83.7 Hounsfield Units [HU] vs 421.3 +/- 54.9 HU, p = 0.77). LCA correlated with CT attenuation of lipid-rich (r = 0.49, p = 0.001) and fibrous plaques (r = 0.32, p < 0.05), but not with that of calcified plaques (r = 0.04, p = 0.81). When plaque attenuation was normalized to LCA, lipid-rich (0.087 +/- 0.036, range - 0.012-0.147) and fibrous plaque attenuation (0.234 +/- 0.056, range 0.153-0.394) were distinct (p < 0.001) with no overlap for both kV groups. CT attenuation was not significantly different between 100-kV and 120-kV groups for lipid-rich (34.0 +/- 21.5 vs 39.3 +/- 12.9, p = 0.33) or fibrous plaques (95.4 +/- 19.1 vs 97.6 +/- 22.0, p = 0.75). Conclusion: Plaque attenuation thresholds for non-calcified plaque components should be adjusted based on LCA. Further adjustment may not be required for different tube potentials.