Cerebral blood flow is essential for normal brain function and often perturbed in neurological disease. If one shines a source of coherent light on perfused tissue, the detected speckles, or "grains" of light fluctuate, or "dance," at a rate proportional to blood flow in the volume sampled by the li ght. In brain tissue, this concept can be harnessed to measure the cerebral blood flow index (CBFi). ...read more read less