Changes in tissue oxyhaemoglobin concentration measured using multichannel near infrared spectroscopy during internal carotid angiography

Objective-To develop an in vivo model for testing spatially resolved spectroscopy and quantified near infrared spectroscopy (NIRS) cerebral blood flow measurements. Method-Multiple detector NIRS has been used to study changes in tissue oxyhaemoglobin (O(2)Hb) concentration during selective internal carotid angiography. A significant reduction in O(2)Hb occurred in tissue interrogated by detectors situated between 0.7 and 4.1 cm from the NIRS light source. Results-The time course of O(2)Hb concentration change was consistent with displacement of oxygenated blood by the radiocontrast medium from vascular beds of differing flow and NIR light attenuation. Increasing changes in O(2)Hb concentration per unit photon path length-predicted to occur at greater emitter-detector separations if those changes had occurred predominantly in cerebral tissue-were found in the first four seconds after injection of radiocontrast medium. However, later changes (6-10 s) were larger and were not proportional to emitter-detector separation. Conclusion-The findings indicate that simple assumptions regarding the distribution of the internal carotid artery blood supply to cerebral and extracerebral tissues, the photon path length through those tissues, and their relative contributions to attenuation of NIR light may not be justified.