Abstract / Summary
Abstract Background Coronary CT angiography (CCTA) requires intravenous iodinated contrast to achieve diagnostic intraluminal opacification. Because reducing the contrast volume administered per examination is an exposure-reduction strategy of practical interest, institutions have explored lower-volume protocols; whether attenuation can be preserved above the diagnostic threshold under real-world, non-randomized implementation is not well documented outside research settings. Methods This retrospective, single-centre, non-concurrent before-and-after protocol-implementation study was conducted at Radiology Center (January 2023–December 2024). From 200 CCTA examinations initially identified from radiology reports as potentially eligible, 106 were excluded (44 body weight >120 kg; 12 beta-blocker administered; 27 coronary calcification/calcium scoring without significant stenosis; 23 motion artefact), leaving 94 CT-angiographically normal examinations: 51 under the standard (pre-reduction) protocol and 43 under the reduced-volume (post-reduction) protocol. All examinations used a third-generation dual-source CT scanner (Siemens SOMATOM Force) with automated tube-voltage selection (CARE kV) and tube-current modulation (CARE Dose4D), retrospective ECG gating, and a 32-cm scan length. Omnipaque 350 mgI/mL was administered by power injector with bolus tracking (ascending aorta ROI, 90 HU trigger, 5 s post-trigger delay). Intraluminal attenuation was measured by a single reader in the left main trunk (LMT) and proximal right coronary artery (RCA); no inter- or intra-observer reproducibility assessment was performed. Distributions were assessed with the Shapiro–Wilk test; normally distributed variables were compared with the independent-samples (Welch) t-test and non-normally distributed variables with the Mann–Whitney U test. A multivariable linear model examined coronary attenuation as a function of protocol epoch, kVp, body weight, heart rate, and iodine delivery rate. Results Contrast volume fell from 63.4 ± 7.3 mL to 49.0 ± 8.0 mL (median 60 [IQR 60–65] vs 45 [45–52.5] mL), a 22.8% reduction (Mann–Whitney p < 0.001), with a corresponding 22.8% reduction in iodine mass (22.20 ± 2.56 vs 17.13 ± 2.79 gI). Iodine delivery rate was essentially unchanged (1.69 ± 0.14 vs 1.69 ± 0.14 gI/s; p = 0.91). Mean LMT attenuation decreased from 520.4 ± 93.6 HU to 451.9 ± 90.7 HU (− 13.2%; t-test p < 0.001) and mean RCA attenuation from 500.2 ± 107.1 HU to 418.1 ± 89.3 HU (− 16.4%; Mann–Whitney p < 0.001). At the per-patient level, 41/43 post-reduction examinations (95.3%; exact 95% CI 84.2–99.4%) reached ≥ 300 HU at the LMT and 39/43 (90.7%; 95% CI 77.9–97.4%) at the RCA; 4/43 examinations, therefore, fell below the SCCT diagnostic threshold at the RCA and 2/43 at the LMT. In the multivariable model, protocol epoch remained independently associated with lower attenuation after adjustment for kVp, weight, heart rate, and iodine delivery rate (LMT: β = − 75.7 HU, 95% CI − 111.6 to − 39.8, p < 0.001; RCA: β = − 87.8 HU, 95% CI − 128.0 to − 47.7, p < 0.001). Mean DLP was 1158.2 ± 637.4 mGy·cm (pre) versus 1072.1 ± 530.6 mGy·cm (post), a non-significant 7.4% difference (Mann–Whitney p = 0.71); the reduction in DLP standard deviation (16.8%) corresponds to an estimated 30.7% reduction in variance, which was not statistically significant (Levene’s test p = 0.24). No renal function or image-quality metric was measured. Conclusion A reduced-volume contrast protocol lowered administered contrast volume and total iodine mass by 22.8% while iodine delivery rate was maintained. Mean coronary attenuation remained above 300 HU in both groups, but a per-patient minority of post-reduction examinations fell below this threshold, particularly at the RCA. Radiation-dose differences were a co-temporal secondary observation and are not attributable to the contrast protocol. Renal outcomes were not assessed, and the findings should not be interpreted as evidence of nephroprotection or as a formal non-inferiority result.