Ph.D Thesis

Ph.D StudentKartvelishvili Liana
SubjectDevelopment of Optical Method for The Measurement of Blood
Flow in Pre-Capillary Tubes
DepartmentDepartment of Aerospace Engineering
Supervisors PROFESSOR EMERITUS Yeshayahou Levy
Full Thesis textFull thesis text - English Version


A new approach of laser Doppler velocimetry designed to measure in vitro blood flow in a glass capillary tube is proposed. The objective is to use the developed method for analyzing retinal hemodynamics. Precise measurement of the RBC velocity properties could be of significant help to the clinician in the early diagnosis and treatment of vascular disease in the retina. 

The Doppler backscattered signal is used for blood flow determination. In this technique, a laser beam of high temporal coherence emitted from a He-Ne laser is bifurcated by diffraction grating. A pair of beams are passed through an optical setup and focused onto the capillary tubes of 200 μm inner diameters. The volume of the beams’ intersection has an ellipsoid shape with interferometric pattern. The backscattered light from the moving particles, is collected by the lens, divided into two parts by the beam splitter and passes onto the pinholes of two photomultiplier tubes. The optical system is aligned to maintain a fixed phase difference between the signals of the two photodetectors. A time shift between two measured signals allows determining the particles’ velocity, stagnation point and flow direction. The signals of the pair of photomultipliers are filtered by low pass-filter and transferred to the computer LabView data acquisition system. Fourier analysis of the photo-detectors signal, obtained from the light scattered by the red blood cells provides a Doppler frequency power spectrum. The cross covariation of the initial signals are used for accurate velocity determination. The shape of this spectrum is dependent on the expected profile of the particles’ velocity.  Stagnation point and velocity direction change are revealed by means of analysis of the Doppler signal, without the need for frequency shifting elements.

The flow velocity was measured in 200 μm diameter glass tubes. The distillate water flow with suspension of polystyrene latex spherical particles (with a diameter of 5 microns) and blood flow with values of haematocrit of 5 % and 40 % were used in the experiments. Flow rate range, used in the measurements, was 1.5-25 ml/h. The ability of the system to measure in high concentrations of RBC particles was studied. It was found that the system measurement error for 5% haematocrit is about 5 % (for flow rate of 10 ml/h). For a haematocrit concentration of 40 %, measurement error was found to be 10 % (also for the case of 10 ml/h flow rate).