A Primer on Diffusion Tensor Imaging of Anatomical Substructures
A Primer on Diffusion Tensor Imaging of Anatomical Substructures
In this article, the authors review the application of diffusion tensor (DT) magnetic resonance (MR) imaging to demonstrate anatomical substructures that cannot be resolved by conventional structural imaging. They review the physical basis of DT imaging and provide illustrative anatomical examples. The DT imaging technique measures the self-diffusion, or random thermal motion, of the endogenous water in nerve tissue. Because of the preferred diffusion of water molecules along the nerve fiber direction, DT imaging can measure the orientation of the neural fiber structure within each voxel of the MR image. The fiber orientation information yielded by DT imaging provides a new contrast mechanism that can be used to resolve images of anatomical substructures that cannot otherwise be visualized using conventional structural imaging. The authors illustrate how DT imaging can resolve individual pathways in the brainstem as well as individual nuclei of the thalamus and conclude by describing potential applications in neurosurgery.
Since the advent of DT imaging in the early 1990s, the technique has generated a tremendous amount of interest in the clinical and laboratory domains. This modality measures the random thermal displacement (that is, Browian motion) of molecules in tissue, typically water molecules. Two aspects of DT imaging render the modality very powerful. First, the microscopic lengthscale of water diffusion in tissue gives DT imaging microscopic spatial sensitivity. Second, in fibrous tissues, such as cerebral white matter or organized gray matter, the diffusion is anisotropic, that is, orientation dependent. The orientation dependence of the diffusion signal enables DT imaging to measure the fiber orientation within each voxel of the image.
In this article, the authors review the application of diffusion tensor (DT) magnetic resonance (MR) imaging to demonstrate anatomical substructures that cannot be resolved by conventional structural imaging. They review the physical basis of DT imaging and provide illustrative anatomical examples. The DT imaging technique measures the self-diffusion, or random thermal motion, of the endogenous water in nerve tissue. Because of the preferred diffusion of water molecules along the nerve fiber direction, DT imaging can measure the orientation of the neural fiber structure within each voxel of the MR image. The fiber orientation information yielded by DT imaging provides a new contrast mechanism that can be used to resolve images of anatomical substructures that cannot otherwise be visualized using conventional structural imaging. The authors illustrate how DT imaging can resolve individual pathways in the brainstem as well as individual nuclei of the thalamus and conclude by describing potential applications in neurosurgery.
Since the advent of DT imaging in the early 1990s, the technique has generated a tremendous amount of interest in the clinical and laboratory domains. This modality measures the random thermal displacement (that is, Browian motion) of molecules in tissue, typically water molecules. Two aspects of DT imaging render the modality very powerful. First, the microscopic lengthscale of water diffusion in tissue gives DT imaging microscopic spatial sensitivity. Second, in fibrous tissues, such as cerebral white matter or organized gray matter, the diffusion is anisotropic, that is, orientation dependent. The orientation dependence of the diffusion signal enables DT imaging to measure the fiber orientation within each voxel of the image.