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Pressure injuries (PIs) originate beneath the surface of the skin at the interface between bone and soft tissue. We used diffuse correlation spectroscopy (DCS) and diffuse near-infrared spectroscopy (DNIRS) to predict the development of PIs by measuring dermal and subcutaneous red cell motion and optical absorption and scattering properties in 11 spinal cord injury subjects with only nonbleachable redness in the sacrococcygeal area in a rehabilitation hospital and 20 healthy volunteers. A custom optical probe was developed to obtain continuous DCS and DNIRS data from sacrococcygeal tissue while the subjects were placed in supine and lateral positions to apply pressure from body weight and to release pressure, respectively. Rehabilitation patients were measured up to four times over a two-week period. Three rehabilitation patients developed open PIs (POs) within four weeks and eight patients did not (PNOs). Temporal correlation functions in the area of redness were significantly different ( p < 0.01 ) during both baseline and applied pressure stages for POs and PNOs. The results show that our optical method may be used for the early prediction of ulcer progression.

Wound size reduction has been the standard benchmark for determination of efficacy for diabetic ulcer treatments but due to interclinician error and difficulty measuring irregular wound shapes, this method is unreliable with a positive predictive value of less than 60%. Diffuse near-infrared spectroscopy (DNIRS) uses 70-MHz modulated light in the diagnostic window (650-900 nm) noninvasively to quantify levels of oxy- and deoxy-hemoglobin in the wound bed, which when measured over time, can show a trend toward or away from healing based on the changes in oxy-hemoglobin concentration from week to week. In this study, DNIRS was used to monitor 24 human diabetic foot ulcers longitudinally over the course of 20 weekly or biweekly measurement sessions. In just 4 weeks, the DNIRS system has an 82% positive predictive value (sensitivity of 0.9 and specificity of 0.86; p < 0.002). These data indicate that it could be possible to predict healing in 4 weeks using DNIRS, which can provide objective guidance toward the continuation of costly treatments. Discontinuing ineffective treatments after 4 weeks could have potentially saved over $12,600 per patient, based on the treatment regimen of patients in this study., (© 2012 by the Wound Healing Society.)

A human study was conducted in which the efficacy of in vivo diffuse near-infrared (NIR) spectroscopy was demonstrated in predicting wound healing in diabetic foot ulcers. Sixteen chronic diabetic wounds were followed and assessed for subsurface oxy-hemoglobin concentration using the NIR device. Weekly measurements were conducted until there was wound closure, limb amputation, or 20 completed visits without healing. Digital photography measured wound size, and the degree of wound contraction was compared with the NIR results. In the 16 patients followed, seven wounds healed, six limbs were amputated, and three wounds remained opened after 20 visits. The initial values in subsurface hemoglobin concentration in all wounds were higher than the nonwound control sites. Healed wounds showed a consistent reduction of hemoglobin concentration several weeks before closure that approached control site values. In wounds that did not heal or resulted in amputation of the limb, the hemoglobin concentration remained elevated. In some cases, these nonhealing wounds appeared to be improving clinically. A negative slope for the rate of change of hemoglobin concentration was indicative of healing across all wounds. In conclusion, evaluation of wounds using NIR may provide an effective measurement of wound healing. NIR spectroscopy can determine wound healing earlier than that visibly assessed by current clinical approaches.

A pilot human study is conducted to evaluate the potential of using diffuse photon density wave (DPDW) methodology at near-infrared (NIR) wavelengths (685 to 830 nm) to monitor changes in tissue hemoglobin concentration in diabetic foot ulcers. Hemoglobin concentration is measured by DPDW in 12 human wounds for a period ranging from 10 to 61 weeks. In all wounds that healed completely, gradual decreases in optical absorption coefficient, oxygenated hemoglobin concentration, and total hemoglobin concentration are observed between the first and last measurements. In nonhealing wounds, the rates of change of these properties are nearly zero or slightly positive, and a statistically significant difference (p<0.05) is observed in the rates of change between healing and nonhealing wounds. Differences in the variability of DPDW measurements over time are observed between healing and nonhealing wounds, and this variance may also be a useful indicator of nonhealing wounds. Our results demonstrate that DPDW methodology with a frequency domain NIR device can differentiate healing from nonhealing diabetic foot ulcers, and indicate that it may have clinical utility in the evaluation of wound healing potential.

The objective of this paper was to correlate optical changes of tissue during wound healing measured by near infrared (NIR) and diffuse reflectance spectroscopy (DRS) with histologic changes in an animal model. Amplitude and phase of scattered light were obtained in a diabetic rat and control model and biopsies were taken for blood vessel ingrowth and collagen concentration. NIR absorption coefficient correlated with blood vessel ingrowth over time, in both the control and diabetic animals. DRS data correlated with collagen concentration. Previous publications by this group documented only the NIR changes during the wound healing process but this is the first reported correlation with histology data. The ability to correlate DRS scattering with collagen concentration during healing is another important and novel finding. This technology may play an important role clinically in assessing the efficacy of wound healing agents in diabetics.

A frequency domain diffuse optical tomography instrument operating in the Near Infrared region (680-830nm) has been designed and used to monitor healing in diabetic wounds in a rat animal model. Instrument design and calibration are described and preliminary data of the in vivo experiment are reported. Excellent discrimination capability between the control and the diabetic population is possible, while the time course of impaired healing in diabetic animals appears to have different optical coefficients from the normal healing in the control group.