An ARX model for light propagation in biological tissue

For many applications in biomedical engineering, and especially for precise dosimetry in photodynamic therapy, it is essential to determine the absorption and scattering of light in biological tissue very precisely. At present it is not possible to measure the absorption and scattering coefficient separately by using an endoscopic sensor based upon the backscattering phenomenon. In this paper, we propose a solution to this problem. We present a new model derived from Kubelka and Munk's theory, which is known to be suitable for the description of optical phenomena in tissue. Then we apply an algorithm often used in signal processing, the Auto Regressive with eXternal input or ARX model, which allows us to determine both optical coefficients separately. A first validation is done by numerical simulation, then measurements with phantoms were done. The results of both tests prove the model to be reliable and effective.