Research papersScan time adapted contrast agent injection protocols with low volume for low-tube voltage CT angiography: An in vitro study

PurposeThe aims of this study were twofold. First, we investigated the extent of changes in arterial peak enhancement and changes in the duration of a diagnostic arterial enhancement when small amounts of CA volumes (≤30 mL) were administered at varying tube voltages. Second, we investigated how to optimize CA injection protocols for CT-angiography with long scan times at various tube voltages to achieve optimal vascular enhancement at the lowest reasonable CA dose.Materials and methodsMeasurements were performed with a custom-made dynamic flow phantom. For CTA protocols with a short scan time, we investigated the effect of various tube voltages (70-120 kVp) on the arterial enhancement profile with very small CA volumes (20 and 30 mL of Iobitridol 350 mg I/mL) at a flow rate of 5 mL/s. For CTA protocols with a long scan time, we utilized an optimized multi-bolus technique switching rapidly between 13 “micro-boli” of CA (total, 60 mL) and saline (total, 24 mL) at a flow rate of 4 mL/s. The peak arterial enhancement (PAE) and the time period of diagnostic aortic enhancement ≥200 HU (T200) were analyzed.ResultsFor the short scan time protocols, a diagnostic peak enhancement was achieved using 20 mL of CA at 70 and 80 kVp (PAE: 327 ± 10 and 255 ± 15 HU, respectively) or 30 mL of CA at 70, 80 and 100 kVp (PAE 451 ± 10, 367 ± 9, and 253 ± 15 HU). For the long scan time, the optimized multi-bolus injection protocol extended T200 at 100 kVp by 6 s (40%) compared to a linear injection protocol (21 ± 1 s and 15 ± 1 s, respectively; p < 0.001).ConclusionOptimized CTA protocols comprising alternations of tube voltage and the CA injection protocol can save radiation doses and CA volumes at the same time.