This paper describes an enhanced noninvasive continuous laser Doppler system for real time blood flow measurement in perfusion regions and larger vessels. The system consists of a miniaturized sensor, a fast digital signal processing (DSP) unit and a PC for signal visualization. The sensor comprises an IR laser diode to illuminate tissue through a short optical fiber with a variable spot size of 400 micrometers to 1000 micrometers and a photodetector which can be positioned 3 mm to 7 mm from the laser spot. The DSP of the system uses a parametric estimation of the laser Doppler power spectrum density based on a first order autoregressive process model AR (1) to calculate the first weighted moment. This algorithm is approximately ten times faster and as accurate as equivalent FFT-based algorithms. With a sampling rate of 390 kHz, it is possible to calculate and visualize 85 flow values per second. Model measurements prove very high linear correlations (r >= 0.99) between calculated first moments and flow velocities in a range from 1 mm/s up to 120 mm/s. Furthermore, in vivo measurement of blood flow both in perfusion regions and larger arteries, such as the a. radialis, were successfully performed in real time.

Date Published: 15 January 1999
PDF: 11 pages
Proc. SPIE 3570, Biomedical Sensors, Fibers, and Optical Delivery Systems, (15 January 1999); doi: 10.1117/12.336946

Published in SPIE Proceedings Vol. 3570:
Biomedical Sensors, Fibers, and Optical Delivery Systems
Francesco Baldini; Nathan I. Croitoru; Martin Frenz; Ingemar Lundstroem; Mitsunobu Miyagi; Riccardo Pratesi; Otto S. Wolfbeis, Editor(s)