Preliminary Evaluation of the Effect of Body Weight on Contrast Enhancement in Coronary CT Angiography: A Fixed Iodine-Dose Protocol

<b>Objective</b>: To assess the effectiveness of a fixed contrast injection protocol-75 mL of contrast followed by 40 mL saline at 5 mL/s with an injection duration of 23 s-in achieving diagnostic enhancement in coronary CT angiography (CCTA) using 64-slice detector CT scanner. <b>Materials and Methods</b>: 456 consecutive patients with suspected coronary disease who underwent CCTA on a 64-slice detector CT scanner between January 2023 and December 2024 and were retrospectively enrolled. Each patient received 75 mL of contrast medium followed by 40 mL of saline at a flow rate of 5 mL/s, with a total injection duration of 23 s. Two radiologists, blinded to patient information, independently measured the contrast enhancement (HU) values in the coronary segments, ascending and descending aorta, and left ventricle. Attenuation levels ≥250 HU were considered diagnostic. Patients were grouped by body weight into two categories: Group 1 (≤75 kg) and Group 2 (>75 kg). The independent t-test and Mann-Whitney U test were used to compare HU values in each vessel between the two groups, while the Chi-square test was applied to compare enhancement success rates (HU ≥ 250) between the groups per vessel. <b>Results</b>: A total of 281 patients (mean age: 51.88 years ± 11.15 [SD]; 167 male, 114 female), were included. Statistically significant differences in the HU enhancement measurements were found between groups (<i>p</i> < 0.001-0.007). However, all segments showed mean and median HU values above 250 HU. Enhancement success rates were significantly higher in Group 1 (<i>p</i> = 0.005-0.04), except in the ascending aorta, descending aorta, left main coronary artery, middle right coronary, distal right coronary artery, and middle left circumflex artery, where the rates were statistically comparable between the groups (<i>p</i> = 0.054-0.61). <b>Conclusions</b>: A fixed contrast protocol (75 mL of contrast medium followed by 40 mL of saline at a 5 mL/s flow rate with a total injection duration of 23 s) appears to be feasible for achieving diagnostic contrast enhancement in CCTA using a 64-slice multidetector CT scanner. This protocol may offer a simplified alternative to individualized, weight-based contrast dosing strategies.