Computer simulation of pressure wave generation in biological media by pulsed lasers with various beam profiles

Pressure waves can be generated in biological tissues by pulsed lasers which deposit optical energy in absorbing structures such as blood vessels. Arrays of acoustic detectors on a tissue surface can sense the arrival of such waves. Analysis of the time-resolved signals can be used to reconstruct the 3-D distribution of the absorbing structures. In this report, a computer simulation was developed (see code listed in Appendix) to predict the time-resolved spatial distribution of pressure in a tissue in response to a pulse laser beam. In particular, the temporal history of pressure generated in a sphere of uniform energy deposition was calculated to illustrate the calibration of the computation. The temporal histories of pressures generated by a flat-field beam and a Gaussian-profile beam are also presented. The results show that the sharp edge of the flat-field beam yields tensile pressure wave and the pressure pattern is significantly different than the pressures produced by the smoother Gaussia-profile beam. The computer simulation is a very simple computation that is a valuable tool for predicting expected experimental results, and may be used in a reconstruction algorithm. This paper can be viewed at http://optics.sgu.ru/SFM/2002/internet/Jacques/index.htm.