Hess C, Mukherjee P (2007). Visualizing White matter Pathways in the Living Human Brain: Diffusion Tensor Imaging and Beyond. Neuroimaging Clin N Am; 17(4): 407-26, vii.
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Diffusion magnetic resonance imaging limitations and future development
Although several white matter atlases have now been made available, a systematic validation of DTI tractography has yet to be undertaken for the large majority of neural pathways that have been cataloged using the technique.
The tracts delineated using DTI tractography lack polarity - there is at present no method that allows the differentiation of afferent and efferent connections. In the future, the orientation of tracts may be inferred by using combined functional MR imaging-diffusion MR imaging paradigms.
The mathematic technique such as HARDI for reconstruction of multi-modal diffusion have had little impact on the underlying physics that govern the measurement of diffusion-weighted MR imaging data, in that diffusion remains an SNR-limited modality. Need to increase spatial resolution, but signal will lose at the same time and increase the uncertainty with the estimated tensor or other diffusion models.
Translate diffusion MR imaging approaches to 7T or higher field strengths and to phased array head coils with increasing numbers of receiver elements can promise the increase of the available SNR, such that higher spatial and angular resolution can be more reliably achieved.
Example of recent approach: tradeoff between angular and spatial resolution for improving SNR by fusing DTI and HARDI information over concentric shells in q-space.
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