A study of the three-dimensional distribution of light (632.8 nm) in tissue

Effective application of photodynamic therapy requires that light dose to tissue be accurately calculated. Special fiber optic detectors have been constructed, and experimental methods developed, for determining three-dimensional flux patterns of red light instilled into tissue. These methods utilize the insertion and movement of the detecting fibers along fixed coordinates within tissue, and the measurement of light flux values at these positions. Resulting values of bovine skeletal muscle have been interpolated and mapped into two-dimensional graphical patterns. Combinations of two-dimensional patterns allow a reconstruction in three dimensions. Either calculation or geometric construction provides penetration depths. Light dispersion is spherically symmetrical, as predicted by diffusion theory. Penetration depths for bovine muscle ranged from 1.8 to 2.3 mm. Three theoretical formulations were fit to the experimental data and were found to be equally valid at depth.