The reliability of an Achilles tendon infrared image analysis method

INTRODUCTION: Prior to utilising smartphone-based thermal imaging for clinical assessment of the Achilles tendon, the intra-rater and inter-rater reliability of the method of analysis must be established, with associated standard error of measurement (SEM) and minimal detectable change (MDC) values. METHOD: A convenience sample of 7 participants (4male, 3female, age 18.57± 1.57 years, height 173.7 ± 6.3cm, weight 73.8 ± 8.1kg) were recruited for the study, for a total of 28 skin temperature (TSk) measurements per camera. Measure- ments were taken using two infrared cameras, one handheld (FLIR E8) and one smartphone-compatible (FLIR ONE), from 0.5m and 1m distances. Regions of interest (ROI) were retrospectively selected using a freeform software ROI tool. RESULTS: The method used to analyse TSk of the midportion of the Achilles tendon demonstrated excellent intra-rater reliability at both 0.5m and 1m distances using the FLIR ONE (ICC = 0.99, ICC = 0.99) and FLIR E8 (ICC = 0.98, ICC = 0.95). There was excellent inter-rater reliability of the method at 0.5m and good inter-rater reliability at 1m with data cap- tured from the FLIR ONE (ICC = 0.97, ICC = 0.79), and excellent ICC's at both distances for the FLIR E8 (ICC = 0.97, ICC = 0.99). CONCLUSIONS: The method of TSk analysis using the FLIR ONE is acceptable at 0.5m and 1m distances, however data capture is recommended for the closer distance