Indocyanine Green (ICG) is an FDA approved, water-soluble tricarbocyanine dye routinely used in clinical settings for measuring cardiac output, liver function, and retinal angiography and has been in use for over 50 years. The chemical formula is C45H47N2O6S2Na and the compound has a molecular weight of 774.96Da (CAS number 3599-32-4). It has a peak absorption in the near-infrared spectrum at 805nm and maximal emission at 835nm. Indocyanine Green (ICG) is rapidly and completely bound to plasma proteins (especially albumin) after intravenous injection in the blood (3). At that point the emission spectrum shifts dramatically and can be excited to the 735nm absorbance - 770nm emission spectrum.