Current Clinical Concerns in CT: Results : Protocols
Abdominal Aorta CTA
1. Is IV contrast routinely needed to make the diagnosis of ruptured abdominal aortic aneurysm? Is there any reference in addition to the comments in Computed Body Tomography by Lee, Sagel and Stanley?
Answer: The reality is that we will always use IV contrast; however, if there is a rupture with blood in the retroperitoneum, you can see it without IV contrast. |
2. Do you do CT abdomen for r/o leaking aneurysm, AAA or impending rupture? What is your protocol?
Answer: We do a CT angiogram with a 30 second delay. I will also routinely get a few delayed scans at 60 seconds. Some people would also recommend select non-contrast scans before the contrast injection, but that usually adds little in my experience (although it will show a bleed if present). |
3. Should delayed imaging be routine in endoluminal graft imaging to avoid missing endoleaks?
Answer: Yes, it should. We routinely get delayed images for our endograft studies. |
References
Rozenblit AM, Patlas M, Rosenbaum AT et al. Detection of endoleaks after endovascular repair of abdominal aortic aneurysms: Value of unenhanced and delayed helical CT acquisitions. Radiology 2003; 227: 426-433.
- Summary: This study involving single detector helical technology demonstrated the utility of unenhanced and delayed acquisitions in patients who are imaged following endovascular repair of a AAA. The protocol involved infusion of 120 to 150 mL of 300 mgI/ml contrast at 3 - 4 ml/second. In most patients, an empiric delay of 25 to 30s seconds was used for arterial phase, with test-bolus technique used in those with heart disease. Seventy-three patients were included, 40 of whom did not have an endoleak and 33 of whom did have an endoleak. Various combinations of series were reviewed (unenhanced + arterial, arterial + delayed, unenhanced + arterial + delayed) to determine the impact of each series on detection sensitivity and exclusion of a leak in the leak-negative group. The results showed that only the complete set of acquisitions (unenhanced + arterial + delayed) resulted in 100% sensitivity for detection of leaks. Furthermore, the unenhanced acquisition enabled discrimination of perigraft calcification from perigraft leaking contrast in 20% of the negative studies, which would have been deemed indeterminate without the unenhanced series.
- Summary: In this study, post-treatment angiography and CT were performed in 40/68 patients who underwent endograft stent placement, and in the final 28 patients, angiographic correlation was conducted in cases with positive CT results. The three-phase post-treatment helical CT protocol included unenhanced, enhanced (45 second delay) and delayed (100 second delay) acquisitions. One-hundred-fifty mL of 300 mgI/ml contrast was infused at 2.5 mL/second. The results elucidated a significant correlation between the number of patent lumbar arteries (specifically 4 or more) visualized preoperatively and the likelihood of a post-treatment endoleak.