Effects of infrared camera angle and distance on measurement and reproducibility of thermographically determined temperatures of the distolateral aspects of the forelimbs in horses

Abstract

To assess effects of camera angle and distance on measurement and reproducibility of thermographically determined temperatures of the distolateral aspect of the forelimbs in horses. Evaluation study. 10 adult horses. Thermographic images of both forelimbs were obtained at 3 times during the day (replicates 1, 2, and 3); maximum surface temperature over 1 region (distolateral aspect of the third metacarpal bone and metacarpophalangeal joint) was measured. Standard images were obtained every 5 minutes for 1 hour with the camera positioned at an angle of 90° and a distance of 1.0 m from the forelimb; additional images were obtained at changed (± 20°) angles or at a 1.5-m distance. At the end of each replicate, 4 sets of additional images were obtained at 2-minute intervals to assess short-term reproducibility. Mean ± SD temperature difference between left and right forelimbs was 0.32° ± 0.27°C (0.58° ± 0.49°F) in standard images. Temperatures measured via standard images were highly correlated with those measured with the camera positioned at changed angles or distance. Mean ± SD differences between temperatures measured via standard images and those measured from changed angles or distance were considered small (≤ 0.22° ± 0.18°C [0.40° ± 0.32°F] for all comparisons). The degree of short-term reproducibility was high. Thermographically determined temperatures were unaffected by 20° changes in camera angle or a 0.5-m increase in camera distance from the forelimb. Minor temperature differences between left and right forelimbs were detected in the study and should be considered during diagnostic investigations.