Diabetic Wound Imaging Using a Noncontact Near-Infrared Scanner

An estimated 15% of all patients suffering with diabetes will develop foot ulcers.¹ To date, clinicians employ visual inspection of the wound site during its standard 4-week healing process via monitoring of surface granulation. However, surface granulation is not an implication of internal healing in many cases. If left untreated immediately, the extent of leg/foot amputation may increase due to lack of response to the treatment.

Near-infrared spectroscopy (NIRS) is an emerging noninvasive and nonionizing technology that can map the changes in hemodynamics in the site of interest (eg, the wounded and healthy tissue site) even up to a few centimeters deep. Researchers have implemented NIRS toward wound healing studies in animals and pilot human subject studies as well.^2-3 Herein, a near-infrared optical scanner (NIROS) is implemented in differentiating healing/nonhealing foot ulcers.

NIROS was set up to image large tissue surfaces (>12 cm²) without contact using an LED-based source and an NIR sensitive camera (IDS, Germany). A custom-developed imaging software is used to acquire diffuse reflected NIR images in real time from the tissue surface. IRB-approved imaging studies were carried out on 4 diabetic subjects with wounds at Somesh’s Diabetic Foot Clinic, Chennai, India (www.ndiabeticfoot.com). Diffuse reflected optical images were acquired from the wound and its surrounding regions in all subjects. The optical contrast of wound:peripheries was estimated from the intensity distribution in the wound with respect to its peripheries. From the qualitative and quantitative analysis, it was observed that there is a negative wound:background optical contrast in nonhealing wounds (see Figures 1a and 1c) compared to a positive wound:background contrast in healing wounds (see Figures 1b and 1d). Healing wounds initially have a higher hemoglobin concentration in the wound site, and with time (in weeks) they tend to decrease and become closer to the hemoglobin concentrations of the normal background.^2-3 On the contrary, nonhealing wounds have a higher hemoglobin concentration that does not decrease with time due to the chronic inflammatory phase of these wounds. Extent of absorption of NIR light is directly proportional to hemoglobin concentration. Hence, a negative optical contrast potentially indicates a greater hemoglobin concentration in the wound site with respect to the surroundings than a healing wound that progressed to cell proliferation stage (where hemoglobin is consumed). Thus, a biometric of positive and negative optical contrast is shown to differentiate healing and nonhealing wounds, with future emphasis on extensive studies to validate the results.

Figure 1.

Near-infrared optical images of diabetic subjects with healing or nonhealing ulcers. The plots in third column correspond to the zoomed out region of interest with the intensity profile at a chosen y-plane. The intensity varies from max to min along the y-axis. All cases employed 710 nm LED light source. Healing wounds show a positive optical contrast, while nonhealing wounds show a negative optical contrast.