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

Purpose: The 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 (≤30mL) 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 Methods: Measurements 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 (70-120kVp) on the arterial enhancement profile with very small CA volumes (20 and 30mL of Iobitridol 350mg I/mL) at a flow rate of 5mL/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, 60mL) and saline (total, 24mL) at a flow rate of 4mL/s. The peak arterial enhancement (PAE) and the time period of diagnostic aortic enhancement ≥200 HU (T200) were analyzed.

Results: For the short scan time protocols, a diagnostic peak enhancement was achieved using 20mL of CA at 70 and 80kVp (PAE: 327±10 and 255±15 HU, respectively) or 30mL of CA at 70, 80 and 100kVp (PAE 451±10, 367±9, and 253±15 HU). For the long scan time, the optimized multi-bolus injection protocol extended T200 at 100kVp by 6s (40%) compared to a linear injection protocol (21±1s and 15±1s, respectively; p<0.001).

Conclusion: Optimized CTA protocols comprising alternations of tube voltage and the CA injection protocol can save radiation doses and CA volumes at the same time.