Velocity measurement accuracy in optical microhemodynamics: experiment and simulation.

Area of Science:

• Biophysics
• Fluid Dynamics
• Biomedical Engineering

Background:

• Micro particle image velocimetry (µPIV) is widely used for blood flow analysis in microvessels.
• Using red blood cells (RBCs) as tracers in µPIV can lead to a large depth of correlation (DOC), potentially reducing measurement accuracy.
• The limitations of RBC-based µPIV for blood flow measurements require further evaluation.

Purpose of the Study:

• To investigate the impact of DOC on blood flow measurements using µPIV with RBC tracer particles.
• To evaluate the accuracy of µPIV in determining flow rates and velocity profiles in microvessels.

Main Methods:

• In vitro µPIV experiments were conducted using a 15 µm radius glass tube with 40% hematocrit blood.
• A 3D mechanical RBC-flow model simulated optical speckle patterns at varying hematocrits, tube radii, focus planes, and flow rates.
• Cross-correlating speckle tracking techniques were employed, and measured flows were compared to pump rates and model profiles.

Main Results:

• Both in vitro and in silico models accurately measured flow rates with less than 10% error.
• Hematocrit and tube radius did not significantly influence flow rate measurement precision.
• Velocity profile shape and focus plane location were critical, with errors ranging from 3% to 97%.

Conclusions:

• The large DOC introduced by RBCs affects µPIV image processing for velocity estimation.
• µPIV is acceptable for estimating flow rates if measurements are taken at the vessel's equatorial plane.
• µPIV is not suitable for accurately estimating velocity profile shapes due to the DOC.