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A new imaging method provides structural information on brain tissue previously difficult to access. Diattenuation imaging (DI), developed by scientists at the Forschungszentrum Jülich and the University of Groningen, allows researchers to differentiate, for example, regions with many thin nerve fibers from those with few thick nerve fibers. With the current imaging methods, these types of tissues can not be easily distinguished.
The DI method is based on 3D polarized light imaging (3D-PLI), a neuroimaging technique developed at the Forschungszentrum Jülich, which reveals the pathways of nerve fibers with micrometer resolution. 3D-PLI is used, for example, in the European project Human Brain to study the 3D brain structures of the brain with unprecedented details.
During a 3D-PLI measurement, the histological sections of the brain are illuminated with polarized light. According to the orientation of the direction of oscillation (polarization) relative to the nerve fibers, the light is refracted to different degrees, which allows to calculate the spatial orientation of nerve fibers. This effect – called birefringence – is mainly caused by the myelin sheath, an insulating layer that surrounds many nerve fibers in the brain.
While 3D-PLI measures the refraction of light as a function of polarization, a measure of attenuation determines the attenuation of light as a function of polarization, i.e. the reduction of the intensity of the light. polarized light as it pbades through the part of the brain. The measurement is made with the same device as 3D-PLI, thanks to which two filters are removed.
Scientists have discovered that diattenuation imaging – a combined measure of diattenuation and 3D-PLI – distinguishes different regions of the brain. In some regions, the brain tissue is totally transparent when the polarization of the light is oriented parallel to the nerve fibers. In other regions, the tissue is at most transparent when the polarization is oriented perpendicular to the nerve fibers. The behavior of the tissue depends, among other things, time after the integration of the brain sections.
Using simulations on the former supercomputer Jülich, JUQUEEN, the researchers were able to show that the observed effects also depend on other tissue properties, such as fiber diameter or l? thickness of the myelin sheaths. This makes diattenuation imaging an interesting extension of 3D-PLI, which allows a more precise investigation of brain tissue. In the future, the DI method could be used to study neurodegenerative diseases such as multiple sclerosis or multisystemic atrophy (MSA), which are badociated with changes in the myelin sheath. In addition, the technology makes visible pathological changes and identify regions and types of tissues connected, helping to complex reconstruction of the brain.
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