Multislice CT angiography in post-aortic stent grafting: optimization of scanning protocols for virtual intravascular endoscopy

Abstract

Objective: The aim of this study is to investigate the optimal 64-slice CT scanning protocols of 3D virtual intravascular endoscopy (VIE) visualization in abdominal aortic aneurysm treated with suprarenal stent grafts, based on an in vitro phantom study. Materials and Methods: The study was performed on a human aorta phantom with a commercially available stent graft in situ. The contrast medium was diluted to produce CT attenuation similar to that used in routine abdominal aortic CT angiography. A series of scans was performed on a 64-slice CT scanner with the scanning protocols being section thickness of 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm and 5.0 mm, pitch of 0.9, 1.2 and 1.4 with reconstruction interval of 50% overlap. Quantitative assessment of image quality was performed by measuring the standard deviation (SD) on surfaced rendered VIE images at three anatomic locations, superior mesenteric artery, right renal artery and aortic aneurysm. This aims to determine the degree of stair-step artifacts present on VIE images using a line profile. The thickness of suprarenal stent wires was measured corresponding with each scanning protocol at above same three locations. Subjective assessment of image quality was focused to evaluate the configuration of aortic ostium visualized on VIE images. Results: Our results showed that the SD was independent of section thickness and pitch value, although thinner section thickness of 0.5 mm and 1.0 mm produced better image quality with fewer artifacts. The aortic ostium became irregular or distorted when the section thickness increased to 3.0 mm and 5.0 mm. Radiation dose was inversely proportional to the pitch values. Conclusion: We recommend a scanning protocol of 1.0 mm and pitch 1.4 with reconstruction interval of 0.5 mm as the optimal one of VIE in post-aortic stent grafting as it allows for generation of acceptable images, with fewer artifacts and less radiation dose.