SEPARATION OF CHANGES IN LIGHT-SCATTERING AND CHROMOPHORE CONCENTRATIONS DURING CORTICAL SPREADING DEPRESSION IN RATS

We used near-infrared spectroscopy to separate tissue scattering chang es from changes in cerebral oxyhemoglobin and deoxyhemoglobin and the redox state of cytochrome-c-oxidase. A separate term of the transport scattering coefficient (mu(s)') was included in a modified Lambert-Bee r equation. It is shown by diffusion equation analysis that there is a simple relationship between the differential path-length factor (D-a) and its scattering equivalent (D-s). The method was applied to cortic al spreading depression (CSD) data recorded through the skulls of rats . Biphasic changes in mu(s)' of +/-0.1 mm(-1) were observed during CSD 's that spread with a velocity of similar to 5 mm/min. The method prop osed has the promise to permit monitoring of scattering changes noninv asively in humans during cortical activation or pathophysiological con ditions. (C) 1998 Optical Society of America.