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Fsixtyfour (talk | contribs) m Added cites for digital microscopy |
Fsixtyfour (talk | contribs) m Added cites for static versus dynamic acquisition |
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In static image acquisition only one field of view image is captured at a time. If the user wishes to image other portions of the same sample on the slide, they can use the X-Y positioning hardware (typically composed of two [[linear stage|linear stages]] on the microscope to move to a different area of the slide. Care must be taken to insure that two images do not overlap so as not to count and measure the same particles more than once.
The major drawback to static image acquisition is that it is time consuming, both in sample preparation (getting the sample onto the slide with proper dilution if necessary), and in multiple movements of the stage in order to be able to acquire a statistically significant number of particles to count/measure. Computer-controlled X-Y positioning stages are sometimes used in these systems to speed the process up and to reduce the amount of operator intervention, but it is still a time consuming process, and the motorized stages can be expensive due to the level of precision required when working at high magnification.<ref name=Brown>{{cite web|last=Brown|first=L.|title=Dynamic Versus Static Image Acquisition in Particle Imaging|url=http://www.particleimaging.com/dynamic-versus-static-image-acquisition-in-particle-imaging/|work=www.particleimaging.com|accessdate=2 January 2014}}</ref>
The major advantages to static particle imaging systems are the use of standard microscope systems and simplicity of [[depth of field]] considerations. Since these systems can be made from any standard optical microscope, they may be a lower cost approach for people who already have microscopes. More important, though, is that microscope-based systems have less depth of field issues generally versus dynamic imaging systems. This is because the sample is placed on a microscope slide, and then usually covered with a [[cover slip]], thus limiting the plane containing the particles relative to the [[optical axis]]. This means that more particles will be in acceptable focus at high magnifications.<ref name=Brown />
=== Dynamic imaging particle analysis ===
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[[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.]]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 />
The major advantage to dynamic image acquisition is that it enables acquiring and measuring particles at significantly higher rates of speed, typically on the order of 10,000 particles/minute or greater. This means that statistically significant populations can be analyzed in far shorter time periods than previously possible with manual microscopy or even static imaging particle analysis. In this sense, dynamic imaging particle analysis systems combine the speed typical of [[particle counter|particle counters]] with the discriminatory capabilities of microscopy.<ref name=Brown />
== References ==
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