Determination of optimal exposure time for imaging of blood flow changes with laser speckle contrast imaging.

Laser speckle contrast imaging is becoming an established method for full-field imaging of cerebral blood flow dynamics in animal models. The sensitivity and noise in the measurement of blood flow changes depend on the camera exposure time. The relation among sensitivity, noise, and camera exposure time was investigated experimentally by imaging the speckle contrast changes in the brain after electrical forepaw stimulation in rats. The sensitivity to relative changes in speckle contrast was found to increase at longer exposure times and to reach a plateau for exposure times greater than approximately 2 ms. However, the speckle contrast noise also increases with exposure time and thus the contrast-to-noise ratio was found to peak at an exposure time of approximately 5 ms. Our results suggests that approximately 5 ms is an optimal exposure time for imaging of stimulus-induced changes in cerebral blood flow in rodents.