Feasibility of low concentration iodinated contrast medium in portal venous abdominal imaging: performance of photon-counting CT virtual monoenergetic imaging compared to conventional EID-CT.
PURPOSE To evaluate whether reduced-iodine photon-counting CT (RI-PCCT) virtual monoenergetic imaging (VMI) provides comparable quantitative and non-inferior qualitative image quality compared with standard-iodine energy-integrating detector CT (SI-EIDCT) in portal venous phase abdominal imaging, and to identify the optimal keV range. MATERIALS AND METHODS This retrospective study included 84 adult patients who underwent abdominopelvic PCCT using a lower-concentration iodinated contrast medium (270 mg I/mL) administered at the same injection volume as routine practice, resulting in a reduced total iodine dose, and who had a prior conventional EID-CT performed with standard contrast medium (350 mg I/mL) within one year. Organ-specific contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were calculated across virtual monoenergetic imaging (VMI) levels ranging from 40 to 65 keV and compared with EID-CT. Two independent radiologists assessed subjective image quality at predefined VMI levels (40, 45, and 50 keV) using a 5-point Likert scale. Non-inferiority testing was performed using a predefined margin of -0.5. RESULTS The total iodine dose was significantly lower in the PCCT group than in the EID-CT group (400.60 ± 29.82 vs. 517.88 ± 39.46 mgI/kg, P < 0.001). At 40 keV, RI-PCCT demonstrated higher CNR than SI-EIDCT for the pancreas, portal vein, and spleen (all P < 0.001), whereas liver CNR was similar. SNR showed organ-specific reductions, particularly in the liver. Qualitative scores were lower at 40 keV, but 45 keV and 50 keV met the predefined non-inferiority criterion for all qualitative parameters using a -0.5-point margin. Interobserver agreement was excellent for all qualitative parameters (Gwet's AC2, 0.932-0.975). CONCLUSIONS RI-PCCT provided comparable quantitative and non-inferior qualitative image quality compared with SI-EIDCT, while lowering the iodine and radiation dose. VMI at 45-50 keV provided the optimal balance of contrast and noise, supporting its potential clinical feasibility for routine portal venous phase imaging.