Endovascular thoracic aortic aneurysm repair: evaluating the utility of intravascular ultrasound measurements.

Purpose: To compare intravascular ultrasound (IVUS) and computed tomography (CT) measurements of aortic diameter for the determination of stent-graft sizes used in thoracic endovascular aneurysm repair (TEVAR).

Methods: A retrospective review was conducted of 71 IVUS measurements performed in 33 patients (17 men; mean age 69 years) undergoing endovascular repair for thoracic aortic aneurysm (TAA). For comparison, an inanimate model of the aortic arch and the great vessels was created; 5 independent operators took multiple blinded IVUS measurements. Measurement accuracy is presented as the mean and coefficient of variance in percent.

Results: In 47 (66%) of the 71 clinical measurements, IVUS yielded a value that was larger than the CT scan measurement; in 8 (11%), the difference was at least 5 mm. In the model, CT centerline measurements were accurate within a mean 0.3 mm (0.6%) of the actual diameter; IVUS measurements were accurate within a mean 1.4 mm (2.8%). Centerline IVUS measurements increased the accuracy to within 0.8 mm (1.8%) of the actual diameter.

Conclusion: IVUS measurements of the thoracic aorta were larger than CT measurements 66% of the time. However, there are 2 concerns with IVUS: off-center measurements distort the image and tangential measurements on a curve do not reflect a true centerline diameter. Thus, off-center IVUS measurements or those taken in the tortuous portion of the aorta may not be as accurate as centerline CT measurements.