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Spatial and temporal variations in forearm skin perfusion captured by laser Doppler perfusion imaging (LDI) have been compared with topographic maps recorded by laser Doppler flowmetry. In order to determine the shortest LDI sampling time required at each measurement site, with an adequate signal-to-noise ratio and with the ability to display the heterogeneity in skin perfusion, the noise-limited resolution of the LDI system as well as various sampling times were tested. The noise-limited resolution for medium and high light intensities were less than 0.5% (temporal) and 0.3% (spatial) of full scale. A sampling time of 1 sec was selected and image presentation was made by performing bilinear interpolation between perfusion values. The same area (10 x 10 mm) was mapped with LDI and topographic mapping at seven different sites. In addition, a larger area covering the surrounding skin was recorded with LDI. The small area recordings with LDI and topographic mapping could be identified in the larger LDI image. High-and low-perfusion spots coincided between the two systems. Temporal variations were studied by repeated LDI recordings of the same areas as above. Small spots were selected in the areas and plotted versus time. Without provocation, the total perfusion changes at each spot showed large variations, but the relative perfusion levels between neighboring spots persisted. Provocation with heat increased the perfusion in all spots.

Using a "needle" probe in a template probe holder, we measured the flux and the concentration of moving red blood cell (CMBC) outputs from a Perimed (PF2B) laser-Doppler instrument at 1-mm2 contiguous sites in a 8 x 8-mm area on the flexor forearm of three subjects. Using the means of the flux and CMBC recorded at each spot, a topographic contour map was constructed for each of these parameters. Viewing the two maps together, sites with four different combinations of flux and CMBC could be identified. Trephine biopsies (2 mm) of three representative sites in each subject were performed and the upper plexus was reconstructed in 3 dimensions from serial sections. High flux/high-to-medium CMBC sites were found over the spot where the ascending arterioles entered the upper plexus. Medium flux/medium-to-low CMBC sites and low flux/medium CMBC sites were found in the peripheral part of the vascular unit that was fed by the ascending arteriole. The low flux/low CMBC sites were relatively avascular zones. Video imaging of the upper plexus in the forearm showed the same overall vascular pattern as the contour maps. The highest flux and CMBC signals were recorded when horizontally oriented vessels were present in the upper third of the plexus (400-650 microns below the stratum corneum). Topographic mapping will allow one to selectively identify different microvascular areas in the skin for physiological studies.