Length and Volume
To find out if the volume of a brain region has changed in an experimental group versus the control group, or to calculate the volume of a lesion or injury, the tool to use in stereology is the Cavalieri probe. According to the Cavalieri method of indivisibles, volume can be comprised of an indefinite number of parallel planar area measurements. The volume of the region is quantified by summing areas and multiplying by the section thickness. In stereology, areas are calculated with the point counting method which requires marking points on a defined grid that falls randomly on your region of interest. The random placement of the grid, as well as the systematic random sampling of tissue sections to use in the study, is crucial to obtaining unbiased results.
Plus signs are used to indicate the grid points that are randomly laid over onto the section by the stereology system. If the center of the plus sign lands in the region of interest, then it is marked for quantification. This process is repeated for each tissue section included in the study. Each marked point represents a given area that is summed with the other marked areas, and then multiplied by the section thickness to yield the volume. The results are based on cut thickness so the calculated volume is based on tissue condition prior to histology.
Stereo Investigator makes marking points quick and easy, including the option to have grid points marked automatically by drawing a contour around your region of interest. All of the grid points within the contour will be marked automatically by the software system.
The length of nerve fibers and blood vessels can be quantified using the Space Balls stereology probe. Quantifying fiber length helps with studies examining neuron signal reach, for example. Or, if blood vessel supply is the area of interest, quantifying fiber length can show if blood vessels have changed due to medication administered for a tumor.
Using systematic random sampling to choose sample sites, the virtual spheres of the Space Balls probe are placed within the sample sites to calculate the length. Intersections between the spheres and the fiber or vessel under study are counted to calculate the results.
Length density of the linear biological structures can be quantified as well as the total length of the object. To calculate the density, a regional volume calculated with Cavalieri will be needed as well as results from using the Space Balls probe.
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