Laser Doppler perfusion imaging by dynamic light scattering.

Imaging of tissue perfusion is important in assessing the influence of peripheral vascular disease on microcirculation. This paper reports on a laser Doppler perfusion imaging technique based on dynamic light scattering in tissue. When a laser beam sequentially scans the tissue (maximal area approximately 12 cm *12 cm), moving blood cells generate Doppler components in the back-scattered light. A fraction of this light is detected by a remote photodiode and converted into an electrical signal. In the signal processor, a signal proportional to the tissue perfusion at each measurement point is calculated and stored. When the scanning procedure is completed, the system generates a color-coded perfusion image on a monitor. A perfusion image is typically built up of data from 4,096 measurement sites, recorded during a time period of 4 min. This image has a spatial resolution of about 2 mm * 2 mm. A theory for the system inherent amplification factor dependence on the distance between individual measurement points and detector is proposed and correction measures are presented. The performance of the laser Doppler perfusion imager was evaluated using a flow simulator. The correlation coefficient between the estimated flow parameter and the perfusion through a mechanical flow simulator was calculated to r = 0.996. To assess the sampling depth of the laser beam, light scattering in tissue was simulated by a Monte Carlo technique. The average sampling depth for skin tissue was calculated to 200-240 microns, depending on the blood content.(ABSTRACT TRUNCATED AT 250 WORDS)