Abstract

The knowledge of the light fluence rate distribution inside a biological tissue irradiated by a Laser (or LED) is fundamental to achieve medical treatments. In this paper, a semi-infinite tissue model was considered, and the steady-state photon diffusion equation was solved by means of the 2-D Fourier Transform. This method can be applied to any irradiation source (cylindrically symmetric or not) at the surface of the tissue. Two particular beam shapes are studied: planar irradiation and flat beam with finite radius. The total fluence rate along the depth in tissues was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the effect of the beam radius on the light attenuation. Measurements were performed using a tank filled with a liquid-simulating medium (Milk), illuminated with a LED array (660 nm, 100mm×100mm). Several circular diaphragms were used in order to obtain uniform beams with specific radii. An optical fiber (with an isotropic tip) was used to measure the fluence rate inside the medium. Preliminary experimental results are in agreement with theoretical predictions.

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