National Alliance for Medical Image Computing http://na-mic.org
Diffusion Weighted MRI
National Alliance for Medical Image Computing http://na-mic.org
Diffusion Imaging
S. Maier and M. Kubicki
•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 http://na-mic.org
DTI allows researchers to quantify the diffusion of water in brain tissue
Diffusion for each image voxel is described by 3 perpendicular vectors
1
2
3
1
2
3
Isotropic diffusion occurs when there is no restriction to water movement (e.g., ventricles, CSF)
Anisotropic diffusion occurs when water movement is restricted to one primary direction (e.g., myelinated fibers)
Diffusion Tensors & Anisotropy
National Alliance for Medical Image Computing http://na-mic.org
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.
National Alliance for Medical Image Computing http://na-mic.org
Fractional AnisotropyFractional Anisotropy
Difference in eigenvalues
Directional diffusion
1+ 2 + 3 3
Mean DiffusivityMean Diffusivity
Addition of eigenvalues
Overall diffusion
Diffusivity & Fractional Anisotropy
National Alliance for Medical Image Computing http://na-mic.org
Number of fibers
Size of fibers
Myelination of fibers
Directionality of Fibers
Diffusivity and FA help determine the number, size and myelination of fibers, whereas only FA gives information about directionality.
High Diffusivity Low FA
High FA Low Diffusivity
High Diffusivity Low FA
High FA Low Diffusivity
High Diffusivity Low FA
High FA Low Diffusivity
Low FA Same Diffusivity
High FA Same Diffusivity
Interpreting Diffusivity and FA
National Alliance for Medical Image Computing http://na-mic.org
Fiber Tracking
National Alliance for Medical Image Computing http://na-mic.org
Axonal Fibers Using 3T MR-DTI
Hae-Jeong Park, Ph.D.
Whole-Brain Tractography
National Alliance for Medical Image Computing http://na-mic.org
Automated tools separate fibers on the basis of their shape and projections
Fiber Clustering
National Alliance for Medical Image Computing http://na-mic.org
Fronto-temporal connections
uncinate fasciculus (blue)
inferior occipito-frontal fasciculus (yellow)
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 fMRI 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
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
Anisotropy Analysis
National Alliance for Medical Image Computing http://na-mic.org
300
350
400
450
500
550
right left
RA
normal controls
schizophrenics
M. Kubicki
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.
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
STEP 1
STEP 2
Initial coarse registration done manually
with Slicer Alignment Module.
no gradient DTI gray-aligned SPGR
+
Automatic fine registration using
registration module, with Mutual
Information as the registration metric.
Coregistration of MRI and DTMRI
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 (T2 baseline)
National Alliance for Medical Image Computing http://na-mic.org
Coregistration: Pilot Study Results
left rightgray white gray white
Case3 FA 0.264 0.360 0.254 0.402AA 0.383 0.516 0.379 0.574RA 0.158 0.223 0.151 0.251
ADC 0.817 0.771 0.839 0.763Case45 FA 0.226 0.350 0.261 0.338
AA 0.339 0.467 0.399 0.448RA 0.134 0.215 0.156 0.207
ADC 0.849 0.725 0.874 0.721Case117 FA 0.258 0.375 0.242 0.374
AA 0.396 0.519 0.354 0.514RA 0.154 0.232 0.144 0.232
ADC 0.850 0.743 0.820 0.737Case0590 FA 0.238 0.346 0.221 0.354
AA 0.362 0.492 0.328 0.498RA 0.141 0.212 0.131 0.218
Measurements:FA: Fractional Anisotropy, AA: Absolute Anisotropy, RA: Relative Anisotropy, ADC: Apparent Diffusion Coefficient.
Kang-Uk Lee