Spectral analysis of laser Doppler signals in real time using digital processing.

A versatile spectrum analyser was developed to generate and display laser Doppler shift signals, and derived parameters, continuously in real time using a digital signal processing chip. A major attraction of the system is that it is entirely programmable, so that both the algorithms and the attributes of the system, such as window function and frame overlap, can be easily altered. It was used to investigate the relative merits of a variety of algorithms using a blood-flow phantom. An index based on the first moment of the Doppler power spectrum was found to be the most reliable flow indicator, with linearity extending towards a velocity of 5 mm s-1 for a blood haematocrit of 5%. The system is not limited to analysis based on the fast Fourier transform (FFT), and is suitable for non-linear techniques such as maximum entropy spectral estimation (MESE).

[1]  Sébastien Candel,et al.  Application of nonlinear spectral analysis and signal reconstruction to laser Doppler velocimetry , 1988 .

[2]  H. Hartley.  The Modified Gauss-Newton Method for the Fitting of Non-Linear Regression Functions by Least Squares , 1961 .

[3]  R. Nossal,et al.  Model for laser Doppler measurements of blood flow in tissue. , 1981, Applied optics.

[4]  Oberg Pa,et al.  Laser-Doppler flowmetry. , 1990, Critical reviews in biomedical engineering.

[5]  P. Welch.  The use of fast Fourier transform for the estimation of power spectra: A method based on time averaging over short, modified periodograms , 1967 .

[6]  Luc Duteil,et al.  A Double Wavelength Laser Doppler System to Investigate Skin Microcirculation , 1985, IEEE Transactions on Biomedical Engineering.

[7]  G Ward,et al.  A critical review of laser Doppler flowmetry. , 1990, Journal of medical engineering & technology.

[8]  M. Stern,et al.  In vivo evaluation of microcirculation by coherent light scattering , 1975, Nature.

[9]  H Fujii,et al.  Blood flow observed by time-varying laser speckle. , 1985, Optics letters.

[10]  G. Holloway,et al.  Cutaneous blood flow responses to injection trauma measured by laser Doppler velocimetry. , 1980, The Journal of investigative dermatology.

[11]  C. Burrus,et al.  DFT/FFT and Convolution Algorithms: Theory and Implementation , 1991 .

[12]  Dual diode preamplifier for detection of laser Doppler interference photons , 1991 .

[13]  C E Riva,et al.  Laser Doppler Velocimetry study of the effect of pure oxygen breathing on retinal blood flow. , 1983, Investigative ophthalmology & visual science.

[14]  G Dougherty,et al.  Comparative study of two laser Doppler blood flowmeters. , 1990, Journal of medical engineering & technology.

[15]  Frequency control for a synchronous motor infusion pump , 1991 .

[16]  A. D. Woolfson,et al.  Non-invasive monitoring of percutaneous local anaesthesia using laser-Doppler velocimetry , 1989 .