FIG. 1.

Preprocessing and template-matching process applied to a sample image acquired in the deep white matter. (a) Raw image illustrating crossing fibers from the corticospinal tract in a section stained with a modified Bielschowsky silver impregnation technique; scale bar=100 μm. (b) The same image after spatial filtering and normalization. (c) A color map of the mean orientation at each pixel overlaid on the raw image data. (d) By applying the Rayleigh threshold, color coding of the mean orientation at each pixel is restricted to pixels that have a single preferred orientation. (e) Magnified image selection from white box in (a). The colored geometrical markers represent three pixels that contain either a single fiber (green triangle), two crossing fibers (blue diamond), or background (red square); scale bar=25 μm. (f–j) Similarity maps in respect to discrete templates (upper right corner). Higher similarity values are visible as areas of enhanced contrast and brightness. (k) Graph showing similarity values plotted against template line orientations for each of the three selected pixel regions in (e). The masking threshold level is displayed as a dotted horizontal line (β=0.0024). The color bar indicates detected fiber orientations from 0 to 180°.