Diffusion Tensor (DT) MRI provides unique information about the microscopic mobility of the water molecules in tissues that cannot be obtained with any other medical imaging technique. Diffusion weighted imaging (DWI) has become a powerful routine tool for detecting regions of cell edema in cerebral stroke. DT-MRI is generally used to examine the tracts of myelinated nerves for various white-matter diseases in the brain. However, conventional DT-MRI techniques are very sensitive to magnetic susceptibility artifacts, and cannot achieve very high spatial resolution. There is a substantial need for high-resolution DT-MRI techniques that work in difficult areas such as the optic nerves, brainstem, peripheral nerves, and spinal cord, as well as in the heart and some other organs. Multi-shot DT-MRI techniques could be used to increase spatial resolution and overcome susceptibility artifacts, but are very sensitive to phase errors due to microscopic motions during the large diffusion gradients. This project will complete the development and perform a detailed evaluation of a novel technique for robust high resolution multi-shot DT-MRI. The technique is novel in that it acquires both components of the diffusion prepared magnetization in conjunction with a single diffusion weighting and thereby eliminates non-uniform diffusion weighting due to residual phase in the diffusion weighted transverse magnetization. A navigator echo provides a measure of data quality and allows artifact reduction by dynamic data re-acquisition. For brevity, we refer to the technique as 2D or 3D nav-CADPaW-EPI (navigated composite acquisition of diffusion prepared and weighted magnetization using multi-shot EPI). After successful development, optimization, and testing of the pulse sequence, we will perform a detailed study of the accuracy, repeatability, and anatomic consistency of the resulting DT measurements in the brain, brain stem, optic nerve, and spinal cord. The technique can also be applied to any anatomic region where the susceptibility artifact is severe. The technique developed and tested in this project should ultimately improve the ability to detect early MS lesions in the optic nerve and spinal cord and provide finer detail for white matter tractography uniformly over the entire brain and nervous system.
