 Over the past decade, a technique widely used by ophthalmologists to assess retinal blood flow, near-infrared ICG angiography, has been applied to neurosurgical patients undergoing a wide variety of cerebrovascular procedures. This technique offers the advantage of real-time visualization of cerebral blood flow through the operating microscope at the time the procedure is being performed. Indocyanine green is an ideal agent for imaging vessels as it is tightly bound to plasma albumin, has a short half-life, and maintains an acceptable safety profile. Furthermore, the excitation and emission profiles for ICG lie in the near-infrared wavelengths, which allow penetration and imaging of vessels below a few millimeters of tissue. 