Andy Chon MD, Presenter: Nothing to Disclose

Jeremy Douglas Collins MD, Abstract Co-Author: Nothing to Disclose

James Christopher Carr MD, Abstract Co-Author: Nothing to Disclose

To determine the accuracy of thoracic aortic measurements by ECG-gated non-contrast CT using ECG-gated contrast-enhanced CT Angiography performed in the same examination as the reference standard.

Retrospective review of 25 consecutive patients (19 men, avg age 63.2 yrs) with suspected thoracic aortic aneurysm that underwent both non-contrast and contrast-enhanced examinations for aortic aneurysm. All studies were performed on a dual source scanner. The imaging protocol consisted of a prospectively ECG-triggered non-contrast and C.A.R.E. bolus initiated prospectively ECG-triggered arterial phase acquisitions. Both datasets were reconstructed at 0.75mm collimation with 50% overlap, identical fields of view, and the B26f kernel. kVp and mAs were adjusted based on body habitus, but were identical between the non-contrast and angiographic acquisitions. A single reviewer obtained orthogonal cross-sectional measurements of the thoracic aorta on both datasets at the following levels: annulus, sinuses of Valsalva, sinotubular junction, mid ascending aorta, proximal arch, distal arch and distal descending aorta. Repeat measurements were performed on 10 patients. A significant difference between measurements was defined as 2mm or greater. Confidence in delineating the vessel borders was scored on an interval scale of 0-3.

The maximum dimension of the thoracic aorta was > 5 cm in 6 patients (24%). A significant difference in maximum dimension was found at the annulus, averaging 0.62 cm (p 0.05). Differences in measurements at the sinuses of Valsalva demonstrated a trend towards significance, with an average difference of 0.19 cm. There were no significant differences in vessel border confidence scores except at the annulus (0.8 vs 2.8) and sinuses of Valsalva (2.2 vs 3.0) for non-contrast and arterial phase acquisitions respectively (p<0.05). Intraobserver variability assessed by the intraclass correlation coefficient was 0.79 at non-contrast CT compared with 0.91 at CT angiography.

Thoracic aortic measurements can be reliably obtained on ECG-gated non-contrast thin section CT examinations above the level of the annulus. Work is ongoing to validate these results with two reviewers in a larger patient cohort.

Non-contrast ECG-gated thin-section CT may offer an alternative to non-contrast MR techniques to quantify thoracic aortic size in patients with renal insufficiency.

Chon, A, Collins, J, Carr, J, Comparison of ECG-gated Noncontrast and Arterial-Phase CT in the Quantitative Assessment of Thoracic Aneurysm.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9015356.html