ECG- vs non-ECG-triggered CTAA: Which is better for assessing aortic disease?

An electrocardiograph (ECG)-triggered computed tomography (CT) angiography of the aorta (CTAA) on a single-source scanner generates better image quality and vessel attenuation of the aortic root and ascending aorta than the non-ECG-triggered CTAA, but the former also delivers a higher dose of radiation, a Singapore study has shown.

“Its use should be considered specifically when assessing aortic root [and] ascending aorta pathology,” in particular, suspected acute aortic syndrome, according to the investigators.

Data of 126 patients who underwent CTAA on a single-source CT scanner using ECG-triggered (group 1; n=77) or non-ECG-triggered (group 2; n=49) protocols were assessed retrospectively in this study. The investigators compared radiation doses between the two groups and performed qualitative (4-point scale) as well as quantitative image quality assessments.

In group 1, the mean volume CT dose index was 12.4 mGy, while the mean dose length product and effective dose were 765.8 mGy cm and 13.0 mSv, respectively. These values were markedly higher than those seen in group 2 (mean volume CT dose index, 9.1 mGy; mean dose length product, 624.1 mGy cm; mean effective dose, 10.6 mSv; p<0.001). [Singapore Med J 2024;65:84-90]

In qualitative assessment, group 1 showed superior image quality at the aortic root‒proximal ascending aorta (median 3) than group 2 (median 2; p<0.001). Quantitative assessment revealed ECG-triggered CTAA as having significantly better mean arterial attenuation, signal-to-noise ratio, and contrast-to-noise ratio than non-ECG-triggered CTAA.

“[O]ur study demonstrates that ECG-triggered CTAA on a single-source scanner results in superior image quality and better vessel attenuation of the aortic root and ascending aorta, but a higher radiation dose of approximately 23 percent as compared to non-ECG-triggered CTAA,” the investigators said.

“It should be used when specifically assessing aortic root and ascending aorta pathology, in particular, suspected acute aortic syndrome, as recommended by British Society of Cardiovascular Imaging/British Society of Cardiovascular CT,” they added. [Br J Radiol 2016;89:20150705]

Aortic root

In an earlier study by Bolen and colleagues, researchers showed better image quality and reduced radiation dose with an ECG-triggered CTAA protocol on a dual-source scanner. However, a dual-source scanner is more expensive than a single-source CT scanner, making it not easily available for patients. [AJR Am J Roentgenol 2012;198:931-938]

The difference in image quality between ECG-triggered and non-ECG-triggered CTAA in the current study was most considerable at the aortic root and the ascending aorta, similar to the findings in the Bolen study. [AJR Am J Roentgenol 2012;198:931-938]

“Accurate assessment of the aortic root is of utmost importance in conditions such as Stanford type A dissection, where it is important to ascertain if the dissection flap extends into the coronary arteries,” according to the investigators.

“Another important application is in preprocedural planning, where the aortic root dimensions need to be accurate for device sizing,” they added. [J Vasc Surg 2011;53:942-949; Eur Radiol 2009;19:664-669; Eur Radiol 2017;27:1963-1970]

“Understanding these different imaging protocols for the aorta and their implications will allow the clinician and radiologist to balance conflicting goals of improving image quality and minimizing radiation burden to optimize patient care,” the investigators said.