Applications of computerized interactive morphometry in pathology: I. Tracings and generation of graphic standards

We have studied the use in anatomic pathology of a computerized interactive morphometry system and conditions for reliability and proper interpretation of data obtained by tracings. Because of the ease of operation and direct visualization of the tracings, we prefer touch-sensitive screens to digitizing tablets as optimal interactive peripherals. Because touch screens have fewer sampling points (256 X 256) than tracing tablets, we studied the relationship between point density and accuracy of length and area measurements by tracing models of known dimensions on the touch screen by experimenting with different step sizes ranging from every second to every sixth valid sampling point; we obtained excellent results with step size 6 followed by two-fold smoothing by two-dimensional filtering. We conclude that because of staircase formation, a high point density may be more of a liability than an asset and that the touch screen is satisfactory. By tracing closed figures of variable shapes but known areas we observed that area measurements may be unreliable with certain irregular shapes and we discuss how perimeter to area ratios can be used to compute surface to volume ratios. Finally, the generation of simple calibrated graphic standards over routine pathologic slides makes the system useful for fast diagnostic applications.