Methods of optically monitoring wound healing
Optical changes of tissue during wound healing measured by Near Infrared and Diffuse Reflectance Spectroscopy are shown to correlate with histologic changes. Near Infrared absorption coefficient correlated with blood vessel in-growth over time, while Diffuse Reflectance Spectroscopy (DRS) data correlated with collagen concentration. Changes of optical properties of wound tissue at greater depths are also quantified by Diffuse Photon Density Wave (DPDW) methodology at near infrared wavelengths. The diffusion equation for semi-infinite media is used to calculate the absorption and scattering coefficients based on measurements of phase and amplitude with a frequency domain or time domain device. An increase in the absorption and scattering coefficients and a decrease in blood saturation of the wounds compared to the non wounded sites was observed. The changes correlated with the healing stage of the wound. The methodologies used to collect information regarding the healing state of a wound may be used to clinically assess the efficacy of wound healing agents in a patient (e.g., a diabetic) and as a non-invasive method to detect the progress of wound healing, particularly chronic wounds due to diabetes. The methodology applies to ischemic environments, impaired healing states, and emerging subsurface tissue deterioration, such as in pressure ulcers, venous ulcers, and ubiquitous ulcers.
1. A method of determining if a wound in a human patient is healing, comprising the steps of:
illuminating the wound tissue in the patient with light from a light source;
measuring over time less than ten weeks one or both of the amplitude and phase shift of the light as it propagates through the wound tissue; wherein the illuminating and measuring steps are performed using a diffuse photon density wave (DPDW) device that is a continuous wave, a frequency domain, or a time domain measurement device,
calculating optical absorption coefficients using the measured amplitude or phase shift of the light;
quantifying the concentration of the oxygenated hemoglobin or the total hemoglobin in the wound tissue over a period of time of less than ten weeks from the optical absorption coefficients; and
determining the rate of change of the oxygenated hemoglobin or total hemoglobin concentration over the period of time, wherein a negative rate of change of either the oxygenated hemoglobin or total hemoglobin indicates the wound is healing and a negligible or positive rate of change indicates the wound is not healing.
2. The method of claim 1 , wherein the light has a wavelength between 650 and 870 nm.
3. The method of claim 1 , wherein the light has a near infrared wavelength selected from the group consisting of 685 nm light, 780 nm light, 830 nm light, and 950 nm light.
4. The method of claim 1 , wherein the wound is selected from the group consisting of pressure ulcers, diabetic foot ulcers, ubiquitous ulcers, and venous ulcers.
5. The method of claim 1 , further comprising differentiating a healing wound from a non-healing wound using the rate of change of total hemoglobin concentration over the period of time.
6. The method of claim 1 , wherein the measurements are taken from at least 2 mm below the surface of the wound.
7. The method of claim 1 , comprising determining the statistical variability of the measurements, wherein a higher degree of statistical variability between consecutive measurements relative to the variability in a healing wound indicates a non-healing wound.
8. The method of claim 1 , wherein the period of time is less than five weeks.
9. The method of claim 1 , wherein the concentration is measured up to five times over the period of time.
10. The method of claim 1 , wherein the threshold between the negative rate of change and the negligible rate of change is a change of −0.003 cm −1 /wk in the optical absorption coefficient.