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[Optimization of the scan delay time of 64-slice spiral CT portal venography].

OBJECTIVE
To optimize scan delay time of multi-slice spiral CT portal venography (MSCTP) using test bolus injection.


METHODS
Sixty individuals with no hepatic diseases were randomly divided into 4 groups (A, B, C and D). The time-density curves (TDC) of the portal vein (PV) were acquired by test bolus (15 ml, 5 ml/s) at the level of liver hilus. In the 4 groups, the MSCTP were delayed for 4, 6, 8 and 10 s according to the peak time of TDC, respectively. The maximum CT value of the portal vein and liver parenchyma were recorded. The maximum intensity projection (MIP) and volume rendering (VR) were employed for three-dimensional reconstruction and the image quality of the 4 groups was estimated.


RESULTS
The average peak time of healthy individuals ranged between 24 and 32 s (95% confidence interval) by means of the test bolus (15 ml). Group C (delay time of 8 s) had a much better image quality of the portal vain than the other groups, and the small branches of the portal vein (6th and 7th orders) were clearly visualized; the major portal vein branches (1st to 4th orders) were also enhanced with sharp edges. Although the hepatic vein was also observed in the portal venous phase in group D, the details of the portal vein on the hepatic edge were distinct and well defined.


CONCLUSION
At the injection rate of 5 ml/s, the optimum scan time delayed is 8 to 10 s in normal individuals according to the peak time of the test bolus.