NONGAUSSIAN DIFFUSION BEHAVIOR IN BRAIN

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this research is to develop models of non-random diffusion in the human body using diffusion tensor imaging (DTI) for the investigators and collaborators on the P41 RR09784 ?Center for Advanced MR Technology at Stanford? effort. Studies using high levels of diffusion sensitization (b 2000 sec/mm2) appear to indicate that the ADC has separate components, producing a non-monoexponential signal decay with diffusion sensitization at the higher b values. Studies of proton diffusion at high b values, however, may provide tissue contrast from a ?slower? ADC component (of the biexponential model) that may more relevant to the expanding intracellular compartment (also seen as cytotoxic edema), since it may be in exchange with the ?fast? ADC water population. Upon modeling this, we find that this occurs mostly in white matter where fibers may be crossing, producing non-random diffusion. A faster ADC component dominates at low b values, while at higher b-values, a second, slower ADC component becomes apparent. It is striking to note the large differences and the lack of any observable slow FA tissue contrast. We have finished all anticipated work on this effort and have submitted these results as a published abstract supporting our models.