Propagation of focused and multibeam laser energy in biological tissue

The results of a Monte Carlo simulation of laser beam propagation in turbid media are presented The study was performed to determine whether using a f ocused beam or multiple beams instead of a single collimated beam could imp rove subsurface laser energy delivery in biological tissue. A parametric st udy was carried out to determine both the laser fluence at a target depth a nd the ratio of fluence at the target over surface fluence as a function of tissue properties and the mode of energy delivery. It was found that the r educed scattering coefficient was the primary determinant as to whether mul tibeam or focused beam delivery could be effective. A focused bean was Soun d to be extremely effective in increasing fluence at the target if the dime nsionless reduced scattering coefficient was less than 2. The delivered flu ence, however, was found to be extremely sensitive to tissue properties. A five-beam laser system was found to be less effective at increasing fluence at the target than a focused beam; but the fluence delivered by a five-bea m system was far less sensitive to tissue properties, thereby making accura te dosimetry more feasible. [S0148-0731(00)01205-X].