3D-scanning SAXS

The myelin sheath’s bilayers, spaced ~15nm apart, produce a distinct signal in the SAXS regime. This signal helps us ascertain the myelin concentration, 3D orientation, average bilayer count around axons, and other structural features within the examined volume.

3D-scanning SAXS operates by mapping a thin slice (30-60µm) of fixed brain tissue at a resolution between 50 and 5µm, under various tilt angles relative to the probing beam. By combining signals from the same volume element probed at different tilt angles, we can determine the primary 3D direction of nerve fibers in that volume element.

This method allows us to integrate nanometer-scale information with micrometer-scale mapping for samples spanning several cm².

Our team is striving to quantitatively correlate our findings with a faster technique used at IBI-1 by Markus Axer’s group, known as 3D-PLI. Our method requires large-scale facilities like a synchrotron and takes several hours per cm². In contrast, 3D-PLI can be performed within seconds over vast areas, but it is sensitive to slice birefringence rather than myelin directly, leading to some ambiguities. By correlating signals from both techniques, we aim to identify and resolve these ambiguities more precisely.

Further reading:

Maiti, S., Frielinghaus, H., Gräßel, D. et al.
Distribution and orientation of nerve fibers and myelin assembly in a brain section retrieved by small-angle neutron scattering.
Sci Rep 11, 17306 (2021). https://doi.org/10.1038/s41598-021-92995-2