MRI provides a unique non-invasive window into the brain, yet is limited to millimeter resolution, orders of magnitude coarser than cell dimensions. Here, we show that diffusion MRI is sensitive to the micrometer-scale variations in axon caliber or pathological beading, by identifying a signature power-law diffusion time-dependence of the along-fiber diffusion coefficient. We observe this signature in human brain white matter and identify its origins by Monte Carlo simulations in realistic substrates from 3-dimensional electron microscopy of mouse corpus callosum. Simulations reveal that the time-dependence originates from axon caliber variation, rather than from mitochondria or axonal undulations. We report a decreased amplitude of time-dependence in multiple sclerosis lesions, illustrating the potential sensitivity of our method to axonal beading in a plethora of neurodegenerative disorders. This specificity to microstructure offers an exciting possibility of bridging across scales to image cellular-level pathology with a clinically feasible MRI technique.

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Recent findings on the connection between the dielectric breakdown strength and the contact angle saturation in electrowetting triggered further investigation of the underlying mechanisms towards reporting the consequences of the proposed relation. High sensitivity current measurements are conducted to monitor the dielectric leakage current during a standard electrowetting experiment by testing thin (15–500 nm) dielectric films of materials widely used in microelectronics industry (SiO2, tetra-ethoxy-silane, Si3N4). The measurements confirmed that the current is negligible as long as the applied, direct current, voltage is kept below a critical value at saturation onset. This current, however, exhibits a sharp increase at higher voltages. By exploiting the increased breakdown strength of stacked oxide-nitride-oxide dielectrics, the appearance of the contact angle saturation is inhibited, suggesting the use of such composites for the design of efficient electrowetting devices.