Reproducibility of inter-session human subject wrist (a) and metacarpalphalangeal (MCP) (b) heat distribution index (HDI) measurements. Three thermal images of control human wrists and MCPs were captured once a day on 3 separate days. Each data point represents the mean and standard error of the three images. (c) Comparison of wrist and MCP HDI values in control patients and patients with active arthritis. Solid horizontal lines represent the mean. Dotted line represents proposed cutoff for active arthritis (1.3°C).