The emergence of diffusion tensor imaging (DTI) provides a unique means via water diffusion characteristics to investigate the white matter integrity in the human brain and its impact on neuronal functions. Over the past ten years, DTI has seen gradually increased utility in its application in clinical diagnosis. However, the characterization of white matter integrity using DTI, as it stands today, often lacks tissue specificity. For example, one of the most commonly used quantitative indices, the fractional anisotropy (FA), can be the composite result of multiple sources in axons and myelin. As such, the changes in FA (as well as the related axial and radial diffusivity) often cannot be clearly attributed to a particular origin. In an effort to achieve tissue specificity for DTI, and given the crucial role of myelin in brain maturation and development, we propose to develop a new acquisition technique that can differentiate white matter microstructural changes with sensitivity and specificity to myelin, and make plans to demonstrate its applicability in translational human applications. Specifically, we propose a progressive research plan to: 1) develop a parallel spiral acquisition sequence for high SNR, spatial accuracy and low motion sensitivity using k-space acquisition in sparse matrix (kSPA) and energy spectrum analysis (KESA);2) develop a magnetization transfer contrast prepared, stimulated-echo DTI to sensitively image myelin microstructure and validate the myelin selectivity in vitro;3) validate the myelin-specific DTI in vivo in multiple sclerosis, and carry out initial application in pediatric brains to optimize a comprehensive DTI protocol and evaluate its potentially large impact in pediatric developmental neuroimaging. Because this methodology can help specifically quantify the microstructural changes, in addition to the content, of the myelin, a successful completion of this project can have a direct and immediate impact on better understanding the myelination process during healthy brain maturation, as well as the demyelination process in disease and during aging, thereby leading to wider applications in developmental and clinical neurosciences.
Recent emergence of diffusion tensor imaging (DTI) provides researchers a new means to investigate white matter structure through water diffusional characteristics. However, the resultant maps on diffusion anisotropy often lacks tissue specificity, leading to inconclusive assessment of white matter changes and their impact on brain disorders. We propose here a new DTI technique that can differentiate the microstructural, in addition to the content, changes in myelin from that in axon within the white matter, thereby improving the understanding of their respective roles in brain maturation in developmental brains. A successful completion of this project will greatly improve the tissue specificity of the current DTI methodology, broadening its clinical applicability in developmental neuroimaging.
