A method is disclosed for preoperative identification of a perforator vessel in a flap to be used in reconstructive surgery. The tissue area suitable for a flap is identified by injecting a bolus of ICG into the bloodstream, illuminating the tissue area with excitation light and observing ICG fluorescence through the skin. The location of the perforator vessel in the tissue area is marked on the patients skin. An incision is made in the tissue area and the flap is harvested only after a suitable perforator vessel has been identified.
