Curvature correction in near-infrared spectroscopy for diabetic foot ulcers: a phantom study

Diabetic foot ulcer (DFU) is one of the major causes of non-traumatic lower limb amputation. Our NIRS imaging device (Smartphone base Oxygenation Tool, SPOT) can measure the tissue oxygenation of the wound and aid in wound management. However, the geometries of the DFU are curved, and the detector of the imaging device cannot collect signals from different depth planes, which leads to incorrect tissue oxygenation measurements. Hence, the signal needs to be corrected to get an accurate diagnosis of DFUs. A curvature correction model has been recently developed in terms of height and angle to correct the diffuse reflectance signal obtained from curved geometries via Monte Carlo light propagation-based simulations. Additionally, an experimental based correction model has also been developed using SPOT. According to the initial results, the simulation-based correction model decreased the percentage median error from a range of 9.4% to 9.67% to a range of 0.03% to 2% for the convex curved geometry, whereas the concave curved model did not need any correction. The objective of the study is to validate the correction models via phantom studies and compare the models. Resin based optical phantoms with convex curved geometry, have been used to apply correction models. A low-cost stereoscopic camera is used to obtain the depth map from the curved phantoms, with an accuracy of 99.3%. Ongoing studies are to apply these depth maps along with angle correction and implement curvature correction to the curved phantoms. Furthermore, the diffuse reflectance signal will be acquired from the curved surface and compared with the signal from the flat surface to determine the accuracy of the correction model using our SPOT device.