SPIRAL CT ANGIOGRAPHY OF THE RENAL-ARTERIES - SHOULD A SCAN DELAY BASED ON A TEST BOLUS INJECTION OR A FIXED SCAN DELAY BE USED TO OBTAIN MAXIMUM ENHANCEMENT OF THE VESSELS

Purpose: The purpose of this work was to assess the optimal scan delay for spiral CT angiography (SCTA) of the renal arteries in achieving o ptimal vascular contrast enhancement and to compare the utility of a d elay based on test bolus injection versus that of a fixed scan delay. Method: Seventy patients underwent renal artery SCTA with a 140 mi bol us of contrast agent injected at 3 ml/s. In 35 patients (Group A), a f ixed scan delay of 27 s was used; in the other 35 (Group B), the scan delay was based on the transit time (T-Test) of a test bolus injection . The scan delays in this group were set at T-Test + 5 s (n = 5), T-Te st + 10 s (n = 8), T-Test + 15 s (n = 4), or T-Test + 20 s (n = 18). F or all 70 patients, the time intervals between T-RA (time to scanning the renal arteries) and T-Max (time to maximum aortic enhancement afte r 140 mi bolus injection) were calculated, after which it was determin ed in which group of patients T-RA occurred closest to T-Max. Linear r egression and mean squared error (MSE) were used for statistical analy sis. Results: For Group A, mean T-RA and T-Max were 38 and 50 s, respe ctively. Mean (T-RA - T-Max) was -12 s with MSE of 185,76. For Group B , mean T-RA and T-Max were 45 and 52 s. Mean (T-RA - T-Max) values wer e -15, -12, -11, and -1 s for scan delays Of T-Test + 5 s, T-Test + 10 s, T-Test + 15 s, and T-Test + 20 s, respectively, with MSEs of 253.8 0, 158.00, 137.50, and 30.00. Conclusion: SCTA of the renal arteries w as best performed with a scan delay of T-Test + 20 s. However, analysi s of our data showed that similar results could be expected with a del ay of 44 s.