CHANGES IN TISSUE OXYHEMOGLOBIN CONCENTRATION MEASURED USING MULTICHANNEL NEAR-INFRARED SPECTROSCOPY DURING INTERNAL CAROTID ANGIOGRAPHY

Objective-To develop an in vivo model for testing spatially resolved s pectroscopy and quantified near infrared spectroscopy (NIRS) cerebral blood flow measurements. Method-Multiple detector NIRS has been used t o 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 oxygenate d blood by the radiocontrast medium from vascular beds of differing fl ow and NIR light attenuation. Increasing changes in O(2)Hb concentrati on per unit photon path length-predicted to occur at greater emitter-d etector separations if those changes had occurred predominantly in cer ebral tissue-were found in the first four seconds after injection of r adiocontrast medium. However, later changes (6-10 s) were larger and w ere not proportional to emitter-detector separation. Conclusion-The fi ndings 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 rela tive contributions to attenuation of NIR light may not be justified.