Determination of Scan Delay Time in Spiral CT-Angiography

OBJECTIVE: The usefulness of a test bolus of contrast medium for predicting the optimal scan delay time in spiral CT-angiography (CTA) was determined. MATERIALS AND METHODS: Two axial single level CT studies were performed at the level of the pancreas in 20 patients, first after injection of a 12 ml "test" bolus, second after administration of a 90 ml bolus. The time interval between the start of the test bolus injection and peak aortic enhancement (T-peak) was measured and compared with the time required to reach a 50, 100, and 150 HU level of aortic enhancement after 90 ml bolus injection. RESULTS: The time required to reach 50, 100, and 150 HU enhancement during the 90 ml bolus was largely variable (mean SD 4.9 s). The T-peak varied between 11 and 32 s (mean 20, SD 6.1 s). There was a strong correlation between the T-peak and the time to the different levels of enhancement during the 90 ml bolus (R2 > or = 0.83). The mean time to 50, 100, and 150 HU enhancement was T-peak -3.3 s (SD 2.5 s), T-peak -1.2 s (SD 2.4 s), and T-peak + 1.3 s (SD 2.4 s). CONCLUSION: The injection of a test bolus improves the timing of a spiral CTA acquisition.