Measurement of inner ear blood flow by laser Doppler flowmetry: the optical characteristics and a flow model study of the inner ear

Laser Doppler flowmetry has widely been used to investigate the real time changes of the local blood flow in the inner ear. However the optical properties of the cochlea have not thoroughly been investigated. We have investigated the optical characteristics of the bony layer of the guinea pig cochlea by means of an integrating sphere and determined the absorption and scattering coefficients. A Delrin plate with approximately the same optical properties as the bony layer was used as a model in some of the measurements. In a flow model the geometrical conditions of the cochlea were studied. The flow model consists of a single capillary and the Doppler shifted signals were measured by a single optical fiber. Results show, the changes of the Doppler shifted signals were related to the distance between the photodetector and the scattering medium. From our results we can conclude that the laser Doppler measurements include information on the blood flow in structures deeper than 1 mm below the bone surface (guinea pigs).