Imaging system for nerve and fiber tract morphometry: Components, approaches, performance, and results

This report describes the imaging system that was developed to recognize, count, size, and evaluate shapes of transverse myelinated fiber (MF) profiles in nerves and fiber tracts automatically and by operator interaction. Automatic analysis, without operator interaction, will either miss a variable percentage of small MFs (using thresholds that discriminate against all other tissue profiles) or include most MFs but spuriously detect other tissue profiles (using more sensitive thresholds). Systems such as this must therefore be operator-interactive. The system that was developed will, in a favorable histologic section, automatically detect and border myelin in more than 85% of MFs without inclusion of other tissue elements. The remainder of the MFs are then identified by the operator with the digitizer pen, and the myelin is automatically bordered or, in rare cases, drawn in. Very reliable, reproducible, and rapid measurements of MF number, size, and shape can be obtained with this system. From evaluation of the size and shape of MFs in semithin sections in the light microscope as compared with the same fibers in adjacent thin sections in the electron microscope, measurements by this system can be expressed as if they were obtained on thin sections. Evaluations can be analyzed statistically, with results printed out, displayed on a video screen, and graphed. Such a system will be useful in evaluating and following morphologic changes in number, size, and shape of MFs in development, aging, regeneration, neurotoxicity, and various diseases.