INTRODUCTION TO DIFFUSION TENSOR IMAGING SUSUMU MORI PDF
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Principles of Neural Science. DTI is a sensitive probe of cellular structure that works by measuring the diffusion of water molecules. New diffusion models, scanning paradigms, and analysis methods are continually being developed for diffusion MRI. Note this interpretation is only strictly true in regions where fiber tracts do not cross, fan, or branch.
An introduction to diffusion tensor image analysis
Journal of Psychiatric Research. The parallel diffusivity measure, also called the axial diffusivity, is equal to the largest eigenvalue.
We have tried to include equations for completeness but they are not necessary for understanding the paper. Small three-dimensional objects called glyphs can be used to display information from each tensor eigensystem. The Journal of chemical physics. Resolving crossings in the corticospinal tract by two-tensor streamline tractography: The goal of this review is to give a basic and broad overview of DTI such that the reader may develop an intuitive understanding of this inntroduction of data, and an awareness of its strengths and weaknesses.
Journal of Magnetic Resonance. Magnetic Resonance in Medicine.
The basis of anisotropic water diffusion in the nervous system – a technical review. Finsler tractography for white matter connectivity analysis of the cingulum bundle. This equation describes how the signal intensity at each voxel decreases in the presence of Gaussian diffusion:.
DTI is usually displayed by either condensing the introductlon contained in the tensor into one number a scalaror into 4 numbers to give an R,G,B color and a brightness value. Proceedings of the National Academy of Sciences. Open in a separate window. The perpendicular diffusivity measure, also called the radial diffusivity, is equal to the average of the two smaller eigenvalues.
In addition to streamline tractography, there imaing many other methods [ 5051 ].
An introduction to diffusion tensor image analysis
Dohi T, Kikinis R, editors. Employment of multiple pairs of diffusion gradients double pulsed field gradient diffusion MRI has been shown to increase sensitivity to small size scales [ 9495 ]. Molecular diffusion nuclear magnetic resonance imaging. The trace and MD relate to the total amount of diffusion in a voxel, which is related to the amount of water in the extracellular space.
Finally, DTI is often viewed by estimating the course of white matter tracts through the brain via a process called tractography.
Introduction to Diffusion Tensor Imaging – Susumu Mori – Google Books
Inferring microstructural features and the physiological state of tissues from diffusion-weighted images. The cingulum can be seen in blue, and tesor posterior limb of the internal capsule in green.
Quantification of measurement error in DTI: National Center for Biotechnology InformationU. A fixed step size of one millimeter or less smaller than a voxel is generally used for DTI data.
The measured macroscopic diffusion anisotropy is due to microscopic tissue heterogeneity [ 6 ]. Motor and language DTI Fiber Tracking combined with intraoperative subcortical mapping for surgical removal of gliomas. Together, the eigenvectors and eigenvalues define an ellipsoid that represents an isosurface of Gaussian diffusion probability: In this section we will describe commonly used scalar quantities, which can be divided into two categories: Next, the decreased signal S k is compared to the original signal S 0 to calculate the diffusion tensor D by solving the Stejskal-Tanner equation 1 [ 36 ].
Partial volume effects, where two types of tissue are present in a voxel, can diffuzion a tensor that represents neither tissue well [ 83 ].
Tensor anisotropy measures are ratios of the eigenvalues that are used to quantify the shape of the diffusion. This example compares the diffusion measured parallel and perpendicular to the axons susu,u a white matter fiber tract. The measured quantity is the diffusivity or diffusion coefficient, a proportionality constant that relates diffusive imxging to a concentration gradient [ 8 ] and has units of m m 2 s.
What can we gain? But in clinical research today a higher number of images are almost always used. FA is basically a normalized variance of the eigenvalues:.
Author manuscript; available in PMC Apr 1. The tensor model is only able to represent one major fiber direction in a voxel, thus DTI tractography can be confounded by regions of crossing fibers, as demonstrated schematically in Figure 7.
Automated methods for atlas-based tractography segmentation, that use prior knowledge to select trajectories, have also been developed [ 636064 digfusion, 65666768 ].
The streamline tract-tracing approach works by successively stepping in the direction of the principal eigenvector the direction of fastest diffusion. Genetic influences on brain asymmetry: The diffusion tensor was originally proposed for use in magnetic resonance imaging MRI by Peter Basser in [ 56 ].
Overall, this difficulty in interpretation of DTI is due to the fact that the scale at which diffusion mork measured with DTI is very different from the size scale of individual axons.