Reflectance measurements of layered media with diffuse photon-density waves: a potential tool for evaluating deep burns and subcutaneous lesions

The basic principles of a non-contact, near-infrared technique for the mapp ing of layered tissues are discussed theoretically and verified experimenta lly. The propagation properties of diffuse photon-density waves in tissues depend on the optical properties of the tissue. When a layered medium is ir radiated by amplitude modulated light, the difference in optical properties between the layers is evident in the phase and amplitude of the diffuse re flection coefficient, which is a result of the interference of the partial waves propagating in the different layers. Thus, diffuse photon-density wav es are applicable to the analysis of the structure of layered tissue. The p robing depth is determined by the modulation frequency of the incident ligh t. For modulation frequencies between several hundred megahertz and a few g igahertz, this allows us to analyse the properties of muscle tissue of up t o 4-8 mm below the surface. Experimental results based on chicken breast mu scle are given. As an example, the technique might be of use for evaluating the depth of necrosis and the blood volume fraction in deep burns.