On the number of measurement sites required to assess regional cerebral blood flow by laser-Doppler scanning during cerebral ischemia and reperfusion.

The aim of this study was to determine whether the number of measurement sites affected the precision of regional cerebral blood flow (CBF) assessment by Laser-Doppler (LD). A simulation study was applied based on data obtained by scanning the cortex in 25 rats during baseline conditions, 15 min global cerebral ischemia and reperfusion. Random samples were repeatedly collected from 1 to 100 locations and deviations from the median of the entire CBF data pool (800 locations) were determined. Single location CBF measurements missed the true median by 24.8+/-2.2 LD-units (baseline conditions, n=100 simulations, mean+/-SEM), 2.7+/-0.6 LD-units (ischemia), and 31.9+/-2.4 LD-units (30th min reperfusion), which can be reduced to 10.9+/-1.0 LD-units (baseline), 0.9+/-0.1 LD-units (ischemia), and 15.5+/-1.3 LD-units (30th min reperfusion) by scanning ten locations. Reliability is further improved by scanning 30 sites with deviations of 6.1+/-0.6 LD-units (baseline), 0.4+/-0.0 LD-units (ischemia), and 8.9+/-0.7 LD-units (30th min reperfusion). Single location CBF assessment was sufficient during global ischemia only. In order to keep the deviation from the true flow below 10 LD-units, at least 15 locations are recommended during baseline conditions and 25 during reperfusion. Laser-Doppler scanning improves the reliability and reduces the variability of CBF measurements.