Abstract

Following single dose fractions of 25-50 Gy the brain is subject to a late delayed effect which progresses to necrosis 7-12 months after irradiation. Loss and dilatation of microvessels is observed accompanying and preceding this necrosis but the role of these changes as a cause of necrosis is not established. To study these responses of the microvessels a perfusion method has been developed to selectively stain and thus clearly visualize these vessels. This consists of a vascular perfusion fixation with mixed aldehydes followed by Schiff’s reagent. Stereo-pair composite images of vertical vibratome slices (150 μm) consisting of 6 optical sections 5 μm apart were prepared using an image analysis system. Data obtained from optical sections were compared with those obtained from composite images using the method for vertical slices developed by Gokhale (1992). Morphometry, needed to assess microvessel size, and stereology, needed to estimate length density and volume fraction, were performed on the composite stereo images. Profiles of cut ends of vessels were counted at the same time their widths were measured. Intersections of cycloids and vertical line probes with the projected images of the vessel segments within the reconstructed slices were recorded while a ribbon probe applied to profiles of cut ends of vessels (McMillan, 1992) was used to estimate volume fraction. Correlations were found between the length densities computed from counts of cut capillaries, the estimate made from the vertical slices using Gokhale's method and that computed from volume fraction and average area of vessel cross sections. In spite of vascular changes and necrosis in the white matter no changes in capillary length density, volume fraction or diameters were found in layer VI of the parietal cortex.

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