Microvascular imaging of the unstained human superior colliculus
Mapping of the microvasculature of the human brain in 3D is critical to advance our understanding of fMRI signals. In preclinical studies, suitable stains can be perfused, while for human tissue long postmortem intervals make it difficult to stain the smallest capillaries. Furthermore, 3D reconstruction of vessels from microscopy images in 2D is challenging. We explored the use of synchrotron radiation phase-contrast microtomography (PC-μCT) of 3D blocks of unstained, paraffin-embedded (FFPE) brain stem specimens for mapping the vasculature of the midbrain region.
Beam time at the SYRMEP beamline of the Elettra Synchrotron was obtained and used to acquire images with voxel sizes of (5µm)3 and (1µm)3 from the FFPE midbrain tissue blocks. Vascular structures identified in PC-μCT were validated by follow-up histology of the same specimen. The Deriche-Canny edge detector was used to identify the boundary between tissue and vascular space and allowed segmentation of the vasculature independent of signal variations in PC-μCT. The vessel diameter, vessel length and volume fraction of the vasculature in the superior colliculi were quantified.
From high resolution PC-μCT images, we found the most frequent vessel diameter to be between 8.6–10.2 μm, the volume fraction 2.8 and 4% and the vessel length 332-376mm/mm3. The vasculature of the superior colliculus could be subdivided into two types of vessels with distinctive morphology: peripheral collicular vessels and central collicular vessels.