Tuesday, April 8, 2008

Topographic focusing

There are two basic ways of scanning a glass slide with a specimen. The one way involves using a single microscope objective. The other way involves using an array of microscope objectives in order to get the job done a whole lot faster.
Part of the speed advantage of the array microscope comes from being able to focus much more rapidly on the material on the glass slide with the array microscope than with a single microscope objective. It's a matter of searching out tissue, for instance, in many places at once instead of having to plumb the depth of the slide one spot at a time.
An array microscope searches for biological material on a glass slide in at least 80 places simultaneously. For most slides, the number of points at which tissue is detected reaches 240. It may be as high as 480. An array microscope measures topography of the specimen every 1.6 mm or so. That means that tissue topography whose knowledge is needed for accurate, focused imaging, leaves little to the imagination.
Compare 240 focus points to the 24 focus points or so that a single-objective scanner measures, one at a time. An array microscope is well along in its accurate scanning of a slide by the time that a single-objective scanner gets done with the 24th focus point.
Finally, it turns out that you can connect dense focus measurements of the array microscope to the operations of a histopathology laboratory. We will return to how that's accomplished in a later post.

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