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Diffusion Weighted MRI

Diffusion Weighted MRI. Diffusion Imaging. In an isotropic medium (inside a glass of water for example) water molecules naturally move according to Brownian motion.

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Diffusion Weighted MRI

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  1. Diffusion Weighted MRI

  2. Diffusion Imaging In an isotropic medium (inside a glass of water for example) water molecules naturally move according to Brownian motion. In biological tissues however the diffusion is very often anisotropic. For example a molecule inside the axon of a neuron has a low probability to cross a myelin membrane. Apply gradient in a given direction dark regions correspond to where non Brownian motion has occured. S. Maier and M. Kubicki

  3. l1 l1 l2 l2 l3 l3 Diffusion Tensors & Anisotropy DTI allows researchers to quantify the diffusion of water in brain tissue Diffusion for each image voxel is described by 3 perpendicular vectors Anisotropic diffusion occurs when water movement is restricted to one primary direction (e.g., myelinated fibers) Isotropic diffusion occurs when there is no restriction to water movement (e.g., ventricles, CSF)

  4. Anisotropy Left: Conventional T2W image does not show white matter fiber tracts in the brain. Middle: Anisotropy map highlights the white matter bundles in the brain. Right: The z-map high intensity regions correspond to large out of plane diffusion.

  5. l1+ l2 + l3 3 Diffusivity & Fractional Anisotropy Mean Diffusivity Fractional Anisotropy Addition of eigenvalues Difference in eigenvalues Overall diffusion Directional diffusion

  6. Interpreting Diffusivity and FA Diffusivity and FA help determine the number, size and myelination of fibers, whereas only FA gives information about directionality. Myelination of fibers Number of fibers High FA Low Diffusivity High Diffusivity Low FA High FA Low Diffusivity High Diffusivity Low FA Size of fibers Directionality of Fibers High FA Low Diffusivity Low FA Same Diffusivity High FA Same Diffusivity High Diffusivity Low FA

  7. Fiber Tracking

  8. Axonal Fibers Using 3T MR-DTI Whole-Brain Tractography Hae-Jeong Park, Ph.D.

  9. Fiber Clustering Automated tools separate fibers on the basis of their shape and projections

  10. Fronto-temporal connections inferior occipito-frontal fasciculus (yellow) uncinate fasciculus (blue) IOCC rarely seen in the literature (from Gray’s Anatomy)

  11. Other applications: Neurosurgery, Brain Tumors

  12. White matter fiber tracts and Schizophrenia • There are widespread gray matter deficits reported in MRI structural studies, but fewer reports of white matter abnormalities. • Functional abnormalities are reported in different brain regions and different systems using fMRI and PET. • Several theories link schizophrenia with disconnection between different brain regions.

  13. Cingulum Bundle • The most prominent connection between limbic structures. • Consolidates information by interconnecting thalamus, prefrontal, parietal, temporal lobes (including amygdala, hippocampus and parahippocampal gyrus) with cingulate gyrus. M. Kubicki

  14. Schizophrenia related symptoms most frequently linked with cingulate dysfunction • Thought disorder • Disorganized behavior • Hallucinations • Flattening of affect • Delusions • Lack of attention M. Kubicki

  15. Anisotropy Analysis Coronal sections of diffusion tensor maps show cingulate fasciculi (out of plane diffusion component- coded in orange)(arrows), above the corpus callosum (in plane component- coded in blue). Patient with schizophrenia on the left, comparison subject on the right. Note the difference in area of the bundle. M. Kubicki

  16. Relative anisotropy within cingulate fasciculus Diffusion anisotropy within the left cingulum bundle in schizophrenia group was 7.4 % lower than in normal comparison subjects (mean of the percentage difference for all eight slices), while diffusion anisotropy on the right side within the CB in schizophrenics was only 2 % lower than in normal comparisons. M. Kubicki

  17. Fiber Tractography H.J. Park

  18. Fiber Clustering H.J. Park

  19. Fiber Tractography H.J. Park

  20. Research Challenges • Diffusion Sequences and Image Resolution. • Fiber Tractography. • White Matter Segmentation. • Statistical Analysis. • Current Region Of Interests: • Superior Temporal Gyrus. • Uncinate Fasciculus. • Cingulate Bundle. • Arcuate Fasciculus.

  21. Coregistration of MRI and DTMRI + no gradient DTI gray-aligned SPGR STEP 1 Initial coarse registration done manually with Slicer Alignment Module. STEP 2 Automatic fine registration using registration module, with Mutual Information as the registration metric.

  22. Non Linear Registration Module Alexandre Guimond, Lifeng Liu (CNI), Matthan Caan (LMI).

  23. Coregistration: Qualitative Evaluation. Magenta: MRI (SPGR) Green: DTMRI (T2 baseline)

  24. Measurements:FA: Fractional Anisotropy, AA: Absolute Anisotropy, RA: Relative Anisotropy, ADC: Apparent Diffusion Coefficient. Coregistration: Pilot Study Results Kang-UkLee

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