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Laser Imaging Sees the Pulse Racing

Photonics Spectra
Apr 1999
Robert C. Pini

A laser imaging system is helping researchers to better understand how blood flows through an artificial heart.

Researchers use particle image velocimetry to study blood flow through a mechanical heart, and to pinpoint areas that could cause blood clots or other problems. Courtesy of Jaikrishnan Kadambi.

Surface flaws, discontinuities between surfaces and imperfect flow patterns can cause cells or platelets to stick to the mechanical heart valves and chambers, forming blood clots and causing stroke or an embolism.
To study how this occurs, a team of researchers developed a pulsing mechanical heart complete with synthetic blood. Using a laser-based particle image velocimetry technique to measure blood particle motion over a large area, the scientists are able to track the platelets and cells and see where they begin to stick. Previous blood-flow analyses used Doppler techniques to get point-specific data.
Using 532-nm light at 50 mJ per pulse from an Nd:YAG laser from New Wave Research of Sunnyvale, Calif., the researchers produce two independent images of the blood flow at various sequenced delays. A cylindrical lens converts the beam into a light sheet that illuminates the flow system, creating an image sequence detected by a charge-coupled device camera, using models built by Eastman Kodak Co. in Roch-ester, N.Y., and by Pulnix Inc. in Sunnyvale. Each laser pulse lasts a few nanoseconds and creates a stop-action image of the complicated flow of blood.
Jaikrishnan Kadambi, an engineering professor at Case Western Reserve University, worked with Hiroaki Harasaki, a Cleveland Clinic Foundation researcher, and M.P. Wernet from the NASA Lewis Research Center to create the model.
"We take two independent images, compare them, analyze the image[s] and calculate the distance traveled, and obtain particle size in addition to velocities," Kadambi said.
To simulate blood's viscosity, the team concocted a mixture of water, sodium iodide and xanthan gum. "To this we add different-size particles. When particles, especially platelets, interact with surfaces, they change their behavior pattern and sometimes stick to walls, and that can cause clotting," Kadambi said. "We can look at the interaction of the particles with the surfaces."
According to Upendra Rohatgi, a research scientist at Brookhaven National Laboratory in Brookhaven, N.Y., the calculation of both particle size and velocity is a novel aspect of the work that enables the researchers to calculate shear stresses and pressure changes in the mechanical heart.

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