Diffusion tensor imaging at long diffusion time
by Rane, Swati, Ph.D., GEORGIA INSTITUTE OF TECHNOLOGY, 2009, 101 pages; 3376342

Abstract:

Diffusion Tensor Imaging (DTI) is a well-established magnetic resonance technique that can non-invasively interpret tissue geometry and track neural pathways by sampling the diffusion of water molecules in the brain tissue. However, it is currently limited to tracking large nerve fiber bundles and fails to faithfully resolve thinner fibers. Conventional DTI studies use a diffusion time, tdiff of 30 ms–55 ms for diffusion measurements. This work proposes the use of DTI at long tdiff to enhance the sensitivity of the method towards regions of low diffusion anisotropy and improve tracking of smaller fibers. The Stimulated Echo Acquisition Mode (STEAM) sequence was modified to allow DTI measurements at long tdiff (approximately 200 ms), while avoiding T2 signal loss. For comparison, DTI data was acquired using STEAM at the shorter value of tdiff and with the standard Double Spin Echo sequence with matched signal-to-noise ratio. This approach was tested on phantoms and fixed monkey brains and then translated to in vivo studies in rhesus macaques. Qualitative and quantitative comparison of the techniques was based on fractional anisotropy, diffusivity, three-phase plots and directional entropy. Tensor-field maps and probabilistic connectivity fronts were evaluated for all three acquisitions. Comparison of the tracked nerve pathways showed that fibers obtained at long tdiff were much longer. Further, the optic tract was tracked in ex vivo fixed rhesus brains for cross validation. The optic tract, traced at long tdiff, conformed to the well documented anatomical description, thus confirming the accuracy of tract tracing at long tdiff. The benefits of DTI at long tdiff indeed help to realize the potential of tensor based tractography towards studying neural development and diagnosing neuro-pathologies, albeit the improvement is more significant ex vivo than in vivo.

 
AdvisersXiaoping Hu; Timothy Duong
SchoolGEORGIA INSTITUTE OF TECHNOLOGY
SourceDAI/B 70-11, p. , Dec 2009
Source TypeDissertation
SubjectsNeurosciences; Biomedical engineering
Publication Number3376342
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