Chapter

Anisotropic Diffusion: From the Apparent Diffusion Coefficient to the Apparent Diffusion Tensor

Peter J. Basser and Evren Özarslan

in Diffusion MRI

Published on behalf of Oxford University Press

Published in print November 2010 | ISBN: 9780195369779
Published online September 2012 | e-ISBN: 9780199965144 | DOI: http://dx.doi.org/10.1093/med/9780195369779.003.0006
Anisotropic Diffusion: From the Apparent Diffusion Coefficient to the Apparent Diffusion Tensor

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This chapter provides some conceptual underpinnings of diffusion tensor imaging (DTI). In particular, it explains isotropic and anisotropic diffusion and presents the definition of the apparent diffusion coefficient (ADC) and that of an analogous quantity, the apparent diffusion tensor (ADT). The underlying models and experimental designs used for diffusion nuclear magnetic resonance (NMR) and diffusion tensor NMR are compared. The chapter also describes information contained in the diffusion ellipsoid that one can use to characterize its size, shape, and orientation in diffusion tensor NMR. Intrinsic features of the ADT, such as the trace or mean ADC, the eigenvalues and eigenvectors of the ADT, and the fractional anisotropy (FA), are defined and described. The diffusion tensor NMR experiment can be further generalized to diffusion tensor MRI or DTI; in this context, the meaning of the b-matrix is explained. The notion of a diffusion tensor field is discussed, and DTI “tractography” is described in this context. Limitations of the Gaussian displacement model used in DTI are also addressed, along with new ways to extend the scope and applications of diffusion MRI methods to probe microstructural features not detectable by DTI.

Chapter.  12548 words.  Illustrated.

Subjects: Neuroscientific Techniques

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