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Anisotropically weighted MRI

R I Shrager1, P J Basser

  • 1Physical Sciences Laboratory, Center for Technology, National Institutes of Health, Bethesda, Maryland, USA.

Magnetic Resonance in Medicine
|July 11, 1998
PubMed
Summary
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Generating isotropically weighted MR images requires only two diffusion-weighted images (DWIs). However, creating anisotropically weighted images, which reveal diffusion anisotropy, needs at least seven DWIs for comprehensive tensor and amplitude estimation.

Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Diffusion Tensor Imaging (DTI)
  • Biomedical Engineering

Background:

  • Isotropically weighted MR images reflect bulk diffusion (Trace(D)) and can be acquired using minimal diffusion-weighted images (DWIs).
  • Anisotropically weighted MR images quantify diffusion anisotropy, a more complex measure derived from the diffusion tensor (D).

Purpose of the Study:

  • To establish the minimum number of DWIs required for anisotropically weighted MR imaging.
  • To present a general mathematical framework for constructing both isotropically and anisotropically weighted MR images.

Main Methods:

  • Utilizing linear algebra to analyze the relationship between DWI acquisition and image weighting.
  • Deriving the minimum DWI requirements for estimating the full diffusion tensor and T2-weighted amplitude image.

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Main Results:

  • Isotropic weighting requires a minimum of two DWIs.
  • Anisotropic weighting necessitates a minimum of seven DWIs, which is also sufficient for full diffusion tensor and T2-weighted amplitude estimation.
  • A general mathematical framework for weighted MR image construction was developed.

Conclusions:

  • The number of DWIs critically impacts the type of diffusion information obtainable in MR imaging.
  • Seven DWIs are the minimum requirement for comprehensive diffusion tensor imaging, enabling both isotropic and anisotropic image contrasts.
  • The provided framework facilitates the creation of advanced diffusion-weighted MR contrasts.