Orthogonal measurement of thoracic aorta luminal diameter using ECG-gated high-resolution contrast-enhanced MR angiography

PURPOSE: To compare orthogonal measurements of the thoracic aortic luminal diameter to standard axial measurements within the same patient population using ECG-gated high-resolution contrast-enhanced MR angiography (CE-MRA). MATERIALS AND METHODS: In all, 45 consecutive patients who had undergone CE-MRA for suspected disease of the thoracic aorta were evaluated retrospectively. Two diameter measurement techniques were performed for each patient's thoracic aorta: standard axial and orthogonal to the aorta. Seven anatomic locations along the thoracic aorta were used for measurement. The data obtained were compared using a paired, two-tailed t-test. RESULTS: We found that the aorta diameter measurements acquired from axial MRA images were significantly greater (P < 0.05) than those acquired from images orthogonal to the course of the aorta at six of seven anatomic sites. Overall, standard axial measurements were found to overestimate luminal diameter of the thoracic aorta by 0.24 cm (95% confidence interval [CI]: 0.14, 0.33) compared to orthogonal measurements. 13.3% of the patients were placed into a greater aorta size classification based on the axial versus the orthogonal measurements. CONCLUSION: Standard axial measurements can overestimate vessel size of the thoracic aorta. ECG-gated high-resolution CE-MRA can be used to measure orthogonal diameters of the thoracic aorta.