Imaging particle analysis: Difference between revisions

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Revision as of 17:15, 10 March 2021

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[[File:Basic flow through diag on white.png|thumb|Diagram showing flow-through architecture for dynamic imaging particle analysis.]]In Dynamic image acquisition, large amounts of sample are imaged by moving the sample past the microscope optics and using [[flash (photography)#High speed flash|high speed flash]] illumination to effectively "freeze" the motion of the sample. The flash is [[synchronization|synchronized]] with a high [[shutter speed]] in the camera to further prevent motion blur. In a dry particle system, the particles are dispensed from a shaker table and fall by gravity past the optical system. In fluid imaging particle analysis systems, the liquid is passed across the optical axis by use of a narrow flow cell as shown at right.

[[File:Flow cell Cross Section.png|thumb|Flow cell Cross Section|Diagram showing the flow cell cross-section perpendicular to the optical axis in a dynamic imaging particle analyzer. Credit: Fluid Imaging Technologies, Inc.]]The flow cell is characterized by its depth perpendicular to the optical axis, as shown in the second diagram on right. In order to keep the particles in focus, the flow depth is restricted so that the particles remain in a plane of best focus perpendicular to the optical axis. This is similar in concept to the effect of the microscope slide plus cover slip in a static imaging system. Since depth of field decreases exponentially with increasing magnification, the depth of the flow cell must be narrowed significantly with higher magnifications.

The major drawback to dynamic image acquisition is that the flow cell depth must be limited as described above. This means that, in general, particles larger in size than the flow cell depth can not be allowed in the sample being processed, because they will probably clog the system. So the sample will typically have to be filtered to remove particles larger than the flow cell depth prior to being evaluated. If it is desired to look at a very wide range of particle size, this may mean that the sample would have to be fractionated into smaller size range components, and run with different magnification/flow cell combinations.<ref name=Brown />