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Length Measurement
The length of structures can also be measured by a counting procedure. This interactive tutorial illustrates the measurement of length per unit volume, showing a transmission light microscope image of dendritic processes viewed in a section of known thickness. Measuring the length of the structures seen in the image would not take into account their three-dimensional wanderings up and down in the section. However, any grid lines drawn on the image represent surfaces that extend vertically downwards through the section, and counting the intersections made by the structures with those lines can provide a correct measurement of the total length per unit volume as shown in Equation 1.
The tutorial initializes with a dendritic specimen appearing in the Specimen Image window. The Original button shows the original grayscale image, and the Thresholded and Skeletonized button shows the dendritic structure after processing. The Line Grid shows the grid of lines used for measurement (cycloidal arcs in this example), and their total length. The Grid Overlay button shows the superposition of the grid lines on the structure. The Counting Hits button shows marks for each intersection of the grid lines with the structure, and the number of hits. The Grid Overlay button superimposes a line grid on the image and also displays the number of the times that the grid lines “hit” the boundary. Based on the equation, the calculated length of the structure is 0.071 µm per cubic µm.
Contributing Authors
John C. Russ - Materials Science and Engineering Dept., North Carolina State University, Raleigh, North Carolina, 27695.
Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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