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Zusammenfassung:
Water diffusion in tissues is known to be non-Gaussian. Moreover, two different water regimes have been found in brain tissue and assigned to a bulk-like compartment and water in contact with macromolecules. Multiple water compartments are also evident in relaxographic imagingindicating the presence of relatively rapidly relaxing myelin water and slower relaxing axoplasmic water, which are in slow exchange at the shutter speed of T2relaxationbut atintermediateexchange (depending on the magnetic field strength) at the shutter speed of T1relaxation.While previous research has established that myelin (besides iron)playsan important role in water relaxation and mobilityin brain tissue, relatively little is known about other tissue components.Here, we investigate the influence of the extracellular matrix (ECM) and of membranes in post-mortem brain tissue samples. Digestionof the ECM, which contributes up to 20% to the brain tissue, had a rather subtle effect on T1relaxation. Using a newly developed CLARITY method, which removes lipids from brain tissue while keeping the remainingstructure intact, we found that the slowly diffusingwater compartment vanished while the mobility of the fast pool increased, which directly demonstrates the influence of membranes on water dynamics.
