Reliability of Ultrasound Diameter Measurements in Patients with a Small Asymptomatic Popliteal Artery Aneurysm: An Intra- and Inter-observer Agreement Study

Abstract

In this study the intra- and inter-observer variability of ultrasound measurements of the diameter of the popliteal artery were tested in a group of patients under surveillance for a small (diameter 10-20 mm), asymptomatic popliteal artery aneurysm (PAA). From a group of patients under ultrasound surveillance for bilateral, asymptomatic PAAs, 13 consecutive patients agreed to participate in the study and provided informed consent. The maximum diameter of the popliteal arteries was assessed by a vascular technologist. The same assessment was repeated by a second vascular technologist, unaware of the results of the first measurement. After a week, this protocol was repeated. The intra- and inter-observer reliability of this measurement was calculated using intra-class correlation coefficients (ICCs) and Bland and Altman plots. Of the 10 patients with bilateral and three patients with unilateral PAA, 12 completed the 2 week protocol. A total of 86 measurements were analyzed. The mean diameter of the popliteal arteries was 13.5 ± 3.4 mm. The ICC for the intra-observer reliability of observer 1 was 0.96 (95% CI 0.92-0.99), p < .001 and of observer 2 was 0.98 (95% CI 0.95-0.99), p < .001. The ICC for the inter-observer reliability for the first measurements was 0.96 (95% CI 0.90-0.98), p < .001 and for the second measurements 0.97 (95% CI 0.94-0.99), p < .001. The Bland-Altman plots showed random error, while 95% of the variation was between 0.016 and 0.16, p > .47. The absolute magnitude of the systematic error of both observers was less than 0.135 mm (median 0.00). Ultrasound measurement of the maximum diameter of the popliteal artery is reproducible; hence, it is suitable for making a clinical treatment decision. Its use for surveillance of small, asymptomatic PAAs is justified.