Various MRI approaches have been used to study brain anatomy and function, including novel ways to investigate the brains functional subdivision based on the spatio-temporal structure of spontaneous activity, and ways to reveal microstructural information by studying magnetic susceptibility contrast. Notably, a method to analyze spontaneous brain activity was developed and applied to a publicly available database of fMRI studies. It was demonstrated that, by clustering activity patterns at individual fMRI time frames, brain areas with a functional relationship can be revealed that escape detection by conventional methods. To identify the neurophysiological correlate of these fMRI signals, the analysis method is now being applied to electrical recordings from primate brain. Together with a several other approaches to study spontaneous brain activity, this work has let to a number of publications. AMRI has continued to study brain anatomy by exploiting magnetic susceptibility contrast. A major development over the last year has been the extraction of cellular compartment-specific information in white matter. Magnetic field modeling studies performed by AMRI and two other groups have shown that an anisotropic susceptibility of the myelin sheath will lead to distinct field effects in the various water compartments in white matter, specifically axonal, interstitial, and myelin water. These field effects lead to characteristic signal decay effects that can be observed by multi-echo MRI techniques. Using dedicated experiments on marmoset brain, we have investigated whether analysis of the signal decay curve allows recovering this compartment specific information. One of the goals of this has been to quantify axonal myelination. Promising results in marmosets have led to initial application to healthy human subjects and MS patients, a collaborative project that is ongoing. In parallel, acquisition and analysis techniques are being refined to optimize myelin quantification. One ongoing effort is the use of magnetization transfer contrast to improve the sensitivity, and develop improve understanding of the complex MRI signal generation mechanism in white matter.
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