Optimal scanning protocol of multislice CT virtual intravascular endoscopy in pre-aortic stent grafting: In vitro phantom study

Objective: To investigate the optimal scanning protocol for multislice computed tomography angiography (MSCT) in pre-aortic stent grafting observed with virtual intravascular endoscopy (VIE). Materials and methods: The study was performed on a human abdominal aortic phantom which was housed in a perspex container, filled with contrast medium having CT attenuation similar to that used in the patient's abdominal CT scan. A series of scans were performed on a four-slice multislice CT scanner with the scanning protocols as follows: section thickness of 1.3, 3.2 and 6.5 mm, pitch value of 0.875, 1.25 and 1.75 with reconstruction intervals of 50% overlap. The degree of stair-step artifacts was measured at three different locations, superior mesenteric artery (SMA), renal ostium and the normal abdominal aorta. Standard deviation (S.D.) of the signal intensity measured on surface shaded images was used to determine the image quality. Radiation dose was also recorded in each scanning protocol. Results: The VIE images showed that image quality was not dependant on pitch and section thickness in the visualization of renal ostium and SMA, whereas it was dependant on these two factors at the level of the normal aorta (p < 0.05). It was noticed that when section thickness reached 6.5 mm the SMA and renal ostia became distorted. Radiation dose measured in 1.3 mm protocols was significantly higher that those measured in other section thicknesses (p < 0.05). Conclusion: The scanning protocol of section thickness 3.2 mm, pitch 1.25 with a reconstruction interval of 1.6 mm was recommended as it allows optimal visualization of VIE images of aortic ostia, generation of fewer artifacts and less radiation dose