Validation of computer-based analysis of static ultrasound images of patellar and Achilles tendon enthesis territories

Abstract

Aim: The aim of the present study is to conduct interobserver and intra-observer validation of computer analysis of static ultrasound images of entheseal territories of the Achilles and distal patellar tendons. Methods: Three rheumatologists with varying levels of experience underwent training in the use of ImageJ software for the analysis of 384 pairs of ultrasound images (long and short axis) from recorded studies of the Achilles and patellar tendons of both spondyloarthritis (SpA) patients and controls. Intra-observer and interobserver tests were conducted by calculating the differences in measurements of the same image at two different times by the same observer and by two different observers assessing the same image. The measurements included the area of analysis, the mean grayscale intensity, and the dispersion of grayscale intensity. Results: In the intra-observer test, no measurement showed a difference greater than 15%, ranging from 4.10% to 14.14%. In the interobserver test, no measurement exhibited a difference greater than 16%, ranging from 7.96% to 15.87%. The differences detected were evenly distributed among observers in both the intra-observer and inter-observer tests. Higher differences were detected in the analysis of images obtained from patient studies compared to control studies in almost all measurements. Conclusions: Whether analyzing control or patient ultrasound images of Achilles and patellar tendons, the intra-observer and interobserver agreement of computer-based analysis of static ultrasound images is more than acceptable and predominantly excellent.