INTEROBSERVER VARIABILITY IN MEASURING THE DIMENSIONS OF THE ABDOMINAL-AORTA - COMPARISON OF ULTRASOUND AND COMPUTED-TOMOGRAPHY

Objectives: To examine the interobserver variability in measuring the abdominal aorta by ultrasound (US) and computed tomography (CT). Desig n: A prospective clinical study in a university hospital. Materials: T hirty-three patients whose abdominal aortas were scanned both with CT and US as a part of aneurysm investigation or for a variety of other r easons. Methods: Three radiologists measured abdominal aortic diameter s by US and CT. The interobserver differences (IOD) in US and CT and i ntraobserver differences for CT-US-pairs were analysed by various stat istical methods. A new concept of ''clinically acceptable difference'' (CAD) was adopted denoting differences of less than 5mm. Results: The IOD in US was 2mm or less in 65% of the anteroposterior and 61% of th e transverse measurements and 5mm or more in 11% of the anteroposterio r and 14% in the transverse measurements in 102 observer pairs for all aortas. The IODs were significantly larger in measuring the aneurysma l aortas compared with normal aortas (p < 0.001). The CAD-value for th e aneurysmal aortas was 84% in the anteroposterior and 82% in the tran sverse directions. In CT the IODs were 2mm or less in 62% of the anter oposterior and 66% of the transverse measurements and 5mm or more in 1 2% of both anteroposterior and transverse measurements in 94 observer pairs for all aortas. The CAD-value in the aneurysmal aortas was 91% i n the anteroposterior and 85% in the transverse directions. There was no significant difference between the US and CT CAD-levels. The absolu te CT-US difference of an individual observer was 2mm or less in 54%, 5mm or more in 17% and 10mm or more in 2% of the anteroposterior measu rements in the 95 CT-US pairs. In the transverse direction the corresp onding figures were: 2mm or less in 63%, mm or move 13% and 10mm or mo re in 2% of the pairs. The diameters obtained by LIS were smaller in 8 4% of the cases compared with those of CT in measuring the maximum aor tic diameter in anteroposterior direction, whereas the same figure for the transverse measurements was 59%. Conclusions: Both US and CT meas urements are subject to significant interobserver variability that mus t be taken into account in the clinical follow-up of small abdominal a ortic aneurysms and in screening studies. Neither of these methods can be considered as a 'gold standard'.