MyelTracer: A Semi-Automated Software for Myelin g-Ratio Quantification.

In the central and peripheral nervous systems, the myelin sheath promotes neuronal signal transduction. The thickness of the myelin sheath changes during development and in disease conditions like multiple sclerosis. Such changes are routinely detected using electron microscopy through g-ratio quantification. While g-ratio is one of the most critical measurements in myelin studies, a major drawback is that g-ratio quantification is extremely laborious and time-consuming. Here, we report the development and validation of MyelTracer, an installable, stand-alone software for semi-automated g-ratio quantification based on the Open Computer Vision Library (OpenCV). Compared to manual g-ratio quantification, using MyelTracer produces consistent results across multiple tissues and animal ages, as well as in remyelination after optic nerve crush, and reduces total quantification time by 40-60%. With g-ratio measurements via MyelTracer, a known hypomyelination phenotype can be detected in a Williams Syndrome mouse model. MyelTracer is easy to use and freely available for Windows and Mac OS X [GitHub link, blinded for review].Significance statementAn easy-to-use software suite for g-ratio quantification in myelin ultrastructure micrographs is currently unavailable, but it is much needed to streamline the study of myelin in homeostasis and disease-related conditions. We used computer vision libraries to develop a freely available software to facilitate studies of myelination.