Laser Doppler perfusion imaging in coronary by-pass surgery

Visualizing the spatial distribution of tissue blood flow by laser Doppler perfusion imaging (LDI) reveals a dependence of the system amplification factor on both the distance to the tissue from the detector and the incident angle of backscattered light on the detector surface. This dependence is caused by a changing number of coherence areas on the detector surface during the scanning procedure. By introducing a lens system that slightly diverges the laser beam, the amplification factor dependence on the tissue-detector distance has been eliminated. The amplification factor dependence on the incident beam angle can be automatically compensated for, since this angle is known to the system at each measurement site. These corrective measures have been verified experimentally and implemented in LDI for myocardial perfusion mapping during coronary by-pass surgery.