Particle Image Velocimetry (PIV)

  PIV-setup Copyright: CVEAME Figure 1: PIV-setup

One challenge in the development of implantable devices such as artificial heart valves, blood pumps, total artificial heart or oxygenators is the reduction of hemolysis and thrombogenesis. Hemolysis is induced by suboptimal flow conditions and occurs when erythrocytes are overstressed. Thrombus formation is usually observed in areas of low flow velocities. Therefore, a detailed analysis of flow patterns is necessary for the development of these devices. The analysis is performed using Particle Image Velocimetry (PIV) – a laseroptical, non-invasive flow measurement system.

Methods

PIV has the ability to detect all three velocity components simultaneously in one measurement plane. Since the measurement is based on optical detection, the flow model as well as the model fluid must be transparent. The flow is seeded with micro-particles, which follow the fluid. The particles are then illuminated in a plane by a laser light sheet and the motion is recorded by one or more cameras (Fig.1).

If the time-gap between two images is small enough, a comparison of these two images by statistical evaluation algorithms (e.g. cross-correlation) leads to the detection of the particle displacement. The local displacement and the time-gap result in the local velocity.

The calculation of the velocity-component perpendicular to the measurement plane is made possible by using two cameras, which record the particles simultaneously from different view angles. Time-resolved detection of the flow field is achieved by using high-speed cameras. Three-dimensional, time-averaged flow fields are detectable by manipulating the measurement plane.

Results

Figure 2 shows two typical particle-images of a PIV-measurement. By using statistical evaluation methods the particle-displacement is calculated and displayed as a vector-plot. Beside measurements of blood pumps, artificial heart valves and oxygenators, general flow measurements such as the flow through a model of the human aorta (Fig.3) are performed.

  Particle images Copyright: CVEAME Figure 2: Particle images and resulting velocity vector plot   3D velocity field Copyright: CVEAME Figure 3: 3D velocity field and measurement planes of the flow through the model of a human aorta