Low- Versus High-Concentration Iodine Contrast for Hepatic Multiphase CT in Chronic Liver Disease: Image Quality, Lesion Detectability, and Iodine Load Reduction with Modern MDCT-A Retrospective Non-Inferiority Study.

Background/Objectives: Lower iodine concentration may mitigate nephrotoxicity by decreasing osmolality and viscosity. With modern multidetector CT (MDCT) and hybrid iterative reconstruction, reducing total iodine load without compromising image quality is feasible. We evaluated whether hepatic multiphase CT using low-concentration iodine contrast (LCIC, 270 mg I/mL) provides non-inferior image quality and lesion detectability compared with high-concentration iodine contrast (HCIC, 350 mg I/mL), and we identified iodine dose thresholds for acceptable image quality. Methods: We retrospectively analyzed 179 HCIC and 190 LCIC multiphase CT examinations. Arterial-phase imaging used 100 or 120 kVp; the portal-venous phase used automated tube-voltage modulation. We prespecified a non-inferiority margin of -0.5 for the mean image-quality score. Image quality and diagnostic performance were compared, and iodine dose thresholds for acceptable quality were determined using AUC analysis. Results: Arterial-phase image-quality scores were 4.450 ± 0.462 (HCIC) versus 4.439 ± 0.477 (LCIC) (difference, -0.010; 95% CI, -0.107 to 0.086). Portal-venous scores were 4.430 ± 0.443 and 4.337 ± 0.371, respectively (difference, -0.093; 95% CI, -0.177 to -0.010). Both met non-inferiority. Per-patient diagnostic performance was comparable (0.931 versus 0.947; p = 0.38). Per-lesion detectability was also similar (0.862 versus 0.909; p = 0.18), whereas per-lesion diagnostic performance differed (0.669 versus 0.781; p = 0.02). Optimal iodine dose thresholds were 501.691 mg I/kg at 100 kVp and 599.145 mg I/kg at 120 kVp for the arterial phase, and 517.650 mg I/kg for the portal-venous phase. Conclusions: LCIC hepatic multiphase CT provided non-inferior image quality and diagnostic performance compared with HCIC on contemporary MDCT with hybrid iterative reconstruction. The iodine dose required to preserve image quality varied by tube voltage, supporting tailored protocols.