Duplex laser Doppler perfusion imaging.

A duplex mode for recoding of both spatial and temporal blood perfusion components has been developed and evaluated. This modality, which has been implemented as a software module in the laser Doppler perfusion imager, consists of various local area scan (LAS) configurations. These include single-point recording or multipoint recording after repeated movements of the laser beam in quadratic patterns including 2 x 2 or 4 x 4 measurement sites. For the 2 x 2 and 4 x 4 LAS, the output value constitutes the average perfusion of all values captured within the actual region of interest. The 2 x 2 local area scan is corrected by time shifting the sequentially recorded measurement values at consecutive tissue sites, while the 4 x 4 LAS is presented as a vector of the individual subimages. With the standard setting of 65 msec for the signal integration time at each measurement site, the 1 x 1 and 2 x 2 LAS configurations can capture and reproduce perfusion signals with maximal bandwidths of 7.7 and 1.9 Hz, respectively. System evaluation showed that the signal integration time can be reduced to 45 msec without impaired signal quality, thereby further increasing the system bandwidth with a factor of about 1.5. Skin recordings showed that averaged time traces of adjacent measurement sites improve the signal-to-noise ration and allow for a more reliable analysis of, for example, the reactive hyperemic response. Individual time-trace extraction, however, showed reperfusion patterns that differed markedly between sites.