The transformation of biological structures from a less ordered to a more ordered state is an essential characteristic of development. Conversely, the loss of organization and structure is an essential characteristic of aging and degeneration. We plan to quantitatively assess these changes in a variety of tissue specimens using a new technique that we developed here at the NIH, Diffusion Tensor MRI. We plan to measure several new quantitative MRI parameters that we have developed which are sensitive to microstructural alterations. These parameters, which we derived from the measured effective diffusion tensor, behave like histological or physiological stains for different characteristics of a material's structure, and can be used to elucidate different normal or pathological microstructural features. These MR parameters share another property with other quantitative stains--they are independent of a) the position and orientation of the sample within the MR magnet, b) the direction of the applied diffusion gradients, and c) the choice of the laboratory coordinate system. To measure these quantitative MR parameters we must first estimate an effective diffusion tensor in each voxel from a set of measured DWIs. To facilitate this, we have developed ultra-fast sequences to obtain high-resolution, high-quality, DWIs free of motion or phase encode artifacts. This is done by using interleaved, navigator echo corrected, spin-echo or stimulated echo diffusion weighted EPI. These sequences have been implemented successfully on our 4.7 T GE Omega imager and we see no reason why they couldn't be ported to the two microimagers, which reside in your facility. It is likely that our requirement to acquire many (approx 25) high resolution DWIs can be met by using the new high-S/N Conductus superconducting RF probe.
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