The difference between ultrasound and computed tomography (CT) measurements of aortic diameter increases with aortic diameter: analysis of axial images of abdominal aortic and common iliac artery diameter in normal and aneurysmal aortas. The Tromsø Study, 1994-1995.

OBJECTIVE: To assess agreement between ultrasound and computed tomography (CT) measurements from axial images of normal and aneurysmatic aortic and common iliac artery diameter.

DESIGN: Part of a population health screening for abdominal aortic aneurysm conducted in 1994-1995.

MATERIALS AND METHODS: Three hundred and thirty-four subjects with and 221 subjects without ultrasound-detected aneurysm were scanned with CT. Three technicians and one radiologist measured ultrasonographic diameters and five radiologists measured CT diameters. The paired ultrasound-CT measurement differences were analyzed to assess agreement.

RESULTS: Compared to CT measurements, ultrasound slightly underestimated the diameter in normal aortas and tended to overestimate the diameter in aneurysmal aortas. In 555 ultrasound-CT pairs of measurements, the absolute differences for measurements of maximal aortic diameter were 2 mm or less in 62, 60 and 77% in anterior-posterior, transverse and maximum diameter in any plane, respectively. The corresponding figures for an absolute difference of 5 mm or more were 14, 18 and 8%, respectively. Variability increased with increasing diameter.

CONCLUSIONS: Both ultrasound and CT measurements of abdominal aortic diameter are liable to variability and neither of these methods can be considered to be 'gold standard'. Both methods can be used, while taking variability into consideration when making clinical decisions.