Revisiting test bolus: a plug-and-play solution for cardiac CTA timing

Background: Cardiac computed tomography angiography (CTA) for congenital heart disease (CHD) can be technically challenging, particularly in low-volume centers. Real-time radiologist supervision can strain resources and impact productivity. Objective: To evaluate a standardized, delay-corrected test-bolus timing method for cardiac CTA for CHD. Materials and methods: We performed a retrospective review of cardiac CTA examinations (November 2020 to August 2022), comparing a delay-corrected test-bolus timing cohort to a manually triggered control cohort (institutional standard protocol during the study period). We measured quantitative enhancement (HU) at six regions of interest and assessed aorto-pulmonary differentiation. Continuous variables were compared using Welch t-tests; non-inferiority was assessed using one-sided 95% confidence intervals (margin -50 HU). Results: We analyzed 318 examinations (test-bolus n=98; control n=220). In a pooled non-inferiority analysis (margin -50 HU), the test-bolus method met non-inferiority for absolute aortic enhancement (difference +24.1 HU; one-sided 95% CI lower bound −22.7 HU). For left-sided examinations at 80 kVp, mean aorto-pulmonary separation was greater with test-bolus timing (264.0±225.8 HU) than with manual triggering (40.2±192.3 HU; P<0.001), indicating greater preferential enhancement of the systemic circulation when intended. For both-sided goals at 80 kVp, mean aorto-pulmonary enhancement differences did not differ significantly between groups (P=0.082); median values near 0 in both cohorts were consistent with generally balanced enhancement. Results for both-sided goals at 100 kVp were reported descriptively because of the small test-bolus subgroup size. Conclusion: A patient-specific, real-time physiology-based, internally derived test-bolus framework uses measured contrast dynamics to prescribe scan timing, enabling reliable congenital cardiac CTA with diagnostic-quality target-vessel enhancement across a range of clinical goals.