Multislice CT angiography: Optimization of scan parameters in a vascular phantom.

Purpose: The aim of this study is to determine the optimal scan parameters for the evaluation of experimental vascular stenoses with a multislice-helical CT. Material and Methods: A vascular phantom consisting of four tubes with an inner diameter of 8 mm and with experimental stenoses of 50%, 75% and 90% was scanned in different tube orientations using a multislice-CT scanner (LightSpeed QX/i, GE, Milwaukee, USA). Examinations were performed with increasing collimations (1.25-5mm), tube currents (100-300mA) and two different table speeds (0.75 HQ mode and 1.5 HS mode). Results: The most exact measurements were obtained in tubes angulated parallel to the scan direction with a collimation of 2.5 mm in the HQ mode (7.5 mm/rot.). An almost equivalent accuracy was obtained in the HS mode (15 mm/rot.) with a collimation of 2.5 mm when higher tube currents (300 mA) were employed. The degree of stenoses was overestimated when the tube was angulated perpendicular to the z-axis. Conclusion: Multislice-CT provides a good detection rate of vascular stenoses especially at 0 degrees and also at 45 degrees angulation in the HQ mode. The use of the HS mode with higher tube currents allows scanning of longer distances with almost identical accuracy.