Exploratory Thermal Imaging Assessments of the Feet in Patients with Lower Limb Peripheral Arterial Disease

Peripheral arterial disease (PAD) is an atherosclerotic condition that can result in reduced lower limb tissue perfusion. It is associated with significant comorbidity including coronary artery disease (CAD) and cerebrovascular disease. One of the most currently utilised diagnostic tools is the ankle brachial pressure index, which is time consuming, requires significant user training and is unreliable in diabetics due to vessel calcification leading to falsely elevated results. The aim of this pilot study was to explore the potential use of thermal imaging in identifying PAD. In 44 patients (24 male; mean (SD) age 67 [12] years) thermal images of three regions of interest (ROI’s) on the feet were collected within a normothermic measurement room. The ROI’s for each foot included the first toe (T), proximal foot (PF) and whole foot (WF). The ankle brachial pressure index (ABPI) reference test was collected to make a diagnosis of PAD (ABPI < 0.9). Parametric statistics were employed and a p value <0.05 considered statistically significant. Twenty-three patients had significant PAD in at least one leg (Mean ABPI 0.64; Range 0.32–0.86) while 26 patients had a normal ABPI (non-PAD) in at least one leg (Mean ABPI 1.14; Range 0.9–1.46). There were no significant ROI differences between PAD (Mean WF temperature 30.3 °C; SD 0.8) and non-PAD feet (Mean WF temperature 31.0 °C; SD 0.7) for their mean or SD values. The temperature gradient (toe-proximal foot) was close to −1 °C but this was not significantly different between the groups. Furthermore, right minus left whole foot temperature differences were not significant. Absolute, gradient, spatial and bilateral skin temperature differences of the feet have been quantified in PAD and non-PAD legs and have found no significant differences overall. This pilot study indicates that thermal imaging from resting measurements is unlikely to be of diagnostic value in detecting significant PAD. Furthermore, the study also raises questions about the apparent misconception that in PAD the foot temperatures are usually significantly reduced.