On generalized photocurrent spectral moments and the recovery of speed distribution in laser Doppler flowmetry.

Abstract

Laser Doppler flowmetry (LDF) is a noninvasive method to assess tissue blood flow. By calculating the first moment of the Doppler signal power spectral density, a real-time output is generated that scales linearly with the perfusion flux defined as the product of average speed and concentration of moving blood cells (MBC's) if multiple scattering is negligible. However, this first spectral moment alone is apparently deficient to provide further information about the MBC's under study and therefore unable to answer more intricate questions in LDF. Without assuming any specific MBC speed or scattering vector distribution, a generalized formula for photocurrent spectral moments is first derived in the case of low and moderate MBC concentration. Then as a direct and important use of the formula, the speed distribution of MBC's is obtained via Henyey-Greenstein phase function and a Fourier inversion. The important implications and applications of this formulation in extracting more MBC information are discussed together with some other related issues.