Diffusion Weighted MRI National Alliance for Medical Image

Diffusion Weighted MRI National Alliance for Medical Image Computing http: //na-mic. org

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. National Alliance for Medical Image Computing S. Maier and M. Kubicki http: //na-mic. org

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 l 1 l 2 l 3 Anisotropic diffusion occurs when water movement is restricted to one primary direction (e. g. , myelinated fibers) National Alliance for Medical Image Computing http: //na-mic. org Isotropic diffusion occurs when there is no restriction to water movement (e. g. , ventricles, CSF)

Anisotropy • Left: Conventional T 2 W 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. National Alliance for Medical Image Computing http: //na-mic. org

Diffusivity & Fractional Anisotropy Mean Diffusivity Fractional Anisotropy l 1+ l 2 + l 3 3 Addition of eigenvalues Difference in eigenvalues Overall diffusion Directional diffusion National Alliance for Medical Image Computing http: //na-mic. org

Interpreting Diffusivity and FA help determine the number, size and myelination of fibers, whereas only FA gives information about directionality. Number of fibers High Diffusivity Low FA High FA Low Diffusivity Size of fibers High Diffusivity Low FA High FA Low Diffusivity National Alliance for Medical Image Computing http: //na-mic. org Myelination of fibers High Diffusivity Low FA High FA Low Diffusivity Directionality of Fibers Low FA Same Diffusivity High FA Same Diffusivity

Fiber Tracking National Alliance for Medical Image Computing http: //na-mic. org

Axonal Fibers Using 3 T Whole-Brain MR-DTI Tractography National Alliance for Medical Image Computing http: //na-mic. org Hae-Jeong Park, Ph. D.

Fiber Clustering Automated tools separate fibers on the basis of their shape and projections National Alliance for Medical Image Computing http: //na-mic. org

Fronto-temporal connections inferior occipito-frontal fasciculus (yellow) uncinate fasciculus (blue) IOCC rarely seen in the literature (from Gray’s Anatomy) National Alliance for Medical Image Computing http: //na-mic. org

Other applications: Neurosurgery, Brain Tumors National Alliance for Medical Image Computing http: //na-mic. org

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 f. MRI and PET. • Several theories link schizophrenia with disconnection between different brain regions. National Alliance for Medical Image Computing http: //na-mic. org

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. National Alliance for Medical Image Computing http: //na-mic. org

Schizophrenia related symptoms most frequently linked with cingulate dysfunction • Thought disorder • Disorganized behavior • Hallucinations • Flattening of affect • Delusions • Lack of attention M. Kubicki. National Alliance for Medical Image Computing http: //na-mic. org

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. National Alliance for Medical Image Computing http: //na-mic. org

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. National Alliance for Medical Image Computing http: //na-mic. org

Fiber Tractography H. J. Park National Alliance for Medical Image Computing http: //na-mic. org

Fiber Clustering H. J. Park National Alliance for Medical Image Computing http: //na-mic. org

Fiber Tractography H. J. Park National Alliance for Medical Image Computing http: //na-mic. org

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. National Alliance for Medical Image Computing http: //na-mic. org

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. National Alliance for Medical Image Computing http: //na-mic. org

Non Linear Registration Module Alexandre Guimond, Lifeng Liu (CNI), Matthan Caan (LMI). National Alliance for Medical Image Computing http: //na-mic. org

Coregistration: Qualitative Evaluation. Magenta: MRI (SPGR) Green: DTMRI (T 2 baseline) National Alliance for Medical Image Computing http: //na-mic. org

Coregistration: Pilot Study Results Measurements: FA: Fractional Anisotropy, AA: Absolute Anisotropy, RA: Relative Anisotropy, ADC: Apparent Diffusion Coefficient. Kang-Uk Lee National Alliance for Medical Image Computing http: //na-mic. org