A note on the generalized photocurrent spectral moments in Laser Doppler Flowmetry

Laser Doppler flowmetry (LDF) is used to non invasively assess tissue blood flow. By calculating the first moment of the Doppler signal power spectral density, a continuous output signal is obtained that scales linearly with tissue blood flow defined as the product of the moving blood cells (MBCs) average speed and concentration. The shape of the Doppler signal power spectral density, however, also carries information about the velocity distribution of the MBCs and thereby about what compartment (capillaries or global flow) that generates the Doppler components. By analysing the high order moments of the Doppler signal power spectral density, more information about the qualitative aspects of the tissue blood flow may be revealed. Without assuming any specific MBC speed or scattering vector distribution, a generalized formula is derived in the case of low and moderate MBC concentration. The underestimation of tissue blood flow by the first moment in highly perfused tissue is explained.