Transcript 172_eposter - Stanley Radiology

Diffusion Tensor Imaging: A Pictorial
Review of Physics and Major Fiber
Tract Anatomy of Cerebral White
Matter
Abstract ID No.: IRIA - 1153
Introduction
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Diffusion tensor imaging (DTI) is a magnetic resonance
imaging technique used to characterize the orientational
properties of diffusion of water molecules.
Application of this technique to the brain has been
demonstrated to provide exceptional information on white
matter architecture.
DTI is the only technique available at present for in-vivo
study of white matter tracts.
Physics of DT imaging
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Anisotropic diffusion (directionally dependent) is the basic
principle of DTI.
The direction of maximum diffusivity has shown to coincide
with white matter fiber tract orientation.
Fractional anisotrophy (FA) is a common metric used to
describe the degree of directional diffusivity.
The 3D diffusivity is modeled as an ellipsoid whose orientation
is characterized by 3 eigenvectors whose shape is
characterized by 3 eigenvalues.
Ɛ1, λ1
Ɛ3, λ3
X
Z Ɛ2, λ2
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Aims and Objectives
In this pictorial review, the following are illustrated based on a
study conducted on 20 healthy volunteers:
 Anatomical course of 8 major cerebral white matter tracts.
 Their orientation and conventional colour coding in DTI.
 Average normal range of FA and ADC values.
 Their clinical significance.
Materials and Methods
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DTI images for this study were obtained with the 1.5T system: Philips
Multiva 16 channel; Coil: Head spine coil; Matrix: 112 × 110; FOV: 224
mm; Voxel size: 2 × 2 × 2 mm; Slice thickness: 2 mm; No. of slices: 64;
Isotrophic diffusion encoding in 16 directions; Flip angle: 90°.
DT imaging data were acquired by single shot echo planar imaging
sequence. Diffusion registration is done after finishing DTI scanning, for
distortion correction.
Post processing done in a offline workstation where fiber tracking and FA
value calculations were done using free hand region of interest (ROI)
method.
The convention used for directional colour mapping is red for left to
right, green for anteroposterior and blue for superior-inferior.
Corticospinal, corticopontine &
corticobulbar tracts
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Type: Projection fibers.
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Anatomical course: corticospinal fibers converge into corona radiata
posterior limb of internal capsule
cerebral peduncle. Corticobulbar fibers
converge into corona radiata
genu of internal capsule
cerebral
peduncle
predominantly terminate in cranial motor nuclei. These
bundles run together and are not discriminated on directional DTI
maps.
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Orientation: Superoinferior.
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Colour coding: Blue.
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FA value: 0.50 – 0.60
ADC value (103 mm2/sec): 0.85 – 0.99
Average number of lines in fiber bundle: 150 – 200
Average length of fiber tract (mm): 40 – 60
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Clinical significance:
 Major efferent projection fibers that connect motor cortex to the brain stem and spinal
cord.
 Corticospinal tracts are involved in movement of muscles of body while corticobulbar
tracts are involved in movement of muscles of head.
 Damage of these fibers result in upper motor neuron syndrome characterized by
spasticity, hyperactive reflexes, loss of fine movements and Babinske’s sign.
Corticospinal, corticopontine
& corticobulbar tracts
Geniculocalcarine tract (optic radiation)
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Type: projection fibers.
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Anatomical course: The optic radiation connects the lateral geniculate nucleus
to occipital cortex. The more inferior fibers sweep around posterior horns of
lateral ventricles and terminate in calcarine cortex, more superior fibers take a
strighter, more direct path.
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Orientation: Anteroposterior.
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Colour coding: Green.
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FA value: 0.45 – 0.59
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ADC value (103 mm2/sec): 0.85 – 0.99
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Average number of lines in fiber bundle: 120 – 180
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Average length of fiber tract (mm): 35 – 70
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Clinical significance:
 Transmits visual information from retina of eye to the visual cortex.
 Lesion affecting unilateral optic radiation results in quandrantanopia with
respective superior (or) inferior quandrant of visual field being affected.
Geniculocalcarine tract
(optic radiation)
Internal capsule (Anterior limb)
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Type: projection fibers.
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Anatomical course: Anterior limb - lies between head of candate and rostral
aspect of lentiform nucleus, posterior limb – lies between thalamus and
posterior aspect of lentiform nucleus, Anterior limb – passes thalamocortical
projection fibers to & from thalamus and frontopontine tracts, Posterior limb –
Corticospinal tracts.
Orientation: Anterior limb – Anteroposterior, Posterior limb Superoinferior.
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Colour coding: Anterior limb – green, Posterior limb - blue.
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FA value: 0.45 – 0.59
ADC value (103 mm2/sec): 0.75 – 0.89
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Average number of lines in fiber bundle: 20 – 40
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Average length of fiber tract (mm): 20 – 40
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Clinical significance:
 Spike and wave activity within the thalamocortical network can cause absence seizures
and other forms of epileptic behaviour.
 Thalamocortical dysrhythmia is associated with impulse control disorders such as OCD,
Parkinsons disease, ADHD and other form of chronic psychosis.
 Damage to these fibers can cause loss of consciousness.
 Primary motor cortex sends its axons through posterior limb of internal capsule and
therefore lesions result in contralateral hemiparesis (or) hemiplegia.
Internal capsule
(Anterior limb)
Cingulum
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Type: Association fibers.
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Anatomical course: begins in parolfactory area of cortex below rostrum of
corpus collosum, courses within the cingulate gyrus and arching around the
entire corpus collosum, extends forward into parahippocampal gyrus and uncus.
Orientation: predominant anteroposterior orientation
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Colour coding: green
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FA value: 0.50 - 0.60
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ADC value (103 mm2/sec): 0.80 - 0.89
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Average number of lines in fiber bundle: 70 – 150
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Average length of fiber tract (mm): 30 – 50
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Clinical significance:
 one of the earliest identified brain structure.
 Important brain structure involved in connectivity and integration of information.
 Cognitive functions including attention, visual and spatial skills, working memory.
 Linked to emotion especially apathy and depression. Cingulatomy, surgical severing of
anterior cingulum is a form of psychosurgery used to treat depression and OCD.
Cingulum
Uncinate fasciculus
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Type: Association fibers.
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Anatomical course: Hooks around the lateral fissure to connect the orbital and
inferior frontal gyri of frontal lobe to the anterior temporal lobe.
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Orientation: C shaped fibers.
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Colour coding: colour changes from green to blue as fibers turn from
anteroposterior to superoinferior orientation.
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FA value: 0.45 – 0.55
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ADC value (103 mm2/sec): 0.80 – 0.95
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Average number of lines in fiber bundle: 50 – 100
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Average length of fiber tract (mm): 20 – 40
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Clinical significance:
 Uncinate fasciculus on left side shows greater FA value than on right side. This
relationship is altered in schizophrenia.
 Abnormality in this fasciculus is associated with social anxiety, alzheimer’s disease,
bipolar disorder, depression in elderly.
 Reduced FA in the right uncinate fasciculus is associated with personality traits and
those on left side are associated with general intelligence, verbal and visual memory
and executive performance.
Uncinate fasciculus
Superior longitudinal (arcuate)
fasciculus
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Type: Association fibers.
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Anatomical course: Massive bundle of fibers that sweeps along superior margin
of insula with to and fro fibers connecting frontal lobe to parietal, temporal and
occipital lobe cortices.
Colour coding: colour changes from green to blue as fibers turn from
anteroposterior to superoinferior orientation.
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FA value: 0.45 – 0.50
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ADC value (103 mm2/sec): 0.80 – 0.89
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Average number of lines in fiber bundle: 200 – 500
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Average length of fiber tract (mm): 20 – 30
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Clinical significance:
 Largest association bundle involved with regulating motor behaviour, provides
prefrontal cortex with parietal cortex information regarding perception of visual space.
 Transmits auditory information between superior temporal gyrus and dorsal prefrontal
cortex.
 Tranfers somatosensory information such as language articulation between Broadman
areas 44, 40 & 46.
Superior longitudinal (arcuate)
fasciculus
Inferior longitudinal fasiculus
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Type: Association fibers.
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Anatomical course: Traverses entire length of temporal lobe and connects
temporal and occipital cortices.
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Orientation: Anteroposterior.
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Colour coding: Green.
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FA value: 0.50 - 0.59
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ADC value (103 mm2/sec): 0.80 – 0.95
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Average number of lines in fiber bundle: 30 – 100
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Average length of fiber tract (mm): 50 – 70
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Clinical significance:
 Appears to mediate fast transfer of visual signals to anterior temporal regions.
 Functions of direct ILF pathway is unclear. Future tractography studies of patients with
occipito temporal disconnection syndrome may help define functional role of these
pathways.
Inferior longitudinal
fasiculus
Corpus callosum
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Type: commissural fibers.
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Anatomical course: massive accumulation of fibers connecting corresponding
areas of cortex between the hemispheres.
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Orientation: In Mid-sagittal plane left to right orientation.
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Colour coding: red.
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FA value: 0.60 – 0.65
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ADC value (103 mm2/sec): 0.85 – 0.99
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Average number of lines in fiber bundle: 130 – 200
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Average length of fiber tract (mm): 50 – 60
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Clinical significance:
 Largest
white
matter
fiber
bundle,
facilitates
interhemispheric
communication.
 Anterior callosal lesions results in akinetic mutism or tactile anomia.
 Posterior collosal lesions results in alexia without agraphia.
 Symptoms of refractory epilepsy can be reduced by corpus callosotomy.
 Research has been done on shape of corpus callosum in those with gender
identity disorder.
Corpus callosum
Applications
 DTI promises a wide range of applications in clinical medicine.
 Measures of diffusion tensor have been used to investigate brain
development.
 DTI is a useful tool in providing a road map which aids in neurosurgical
planning.
 Parameters derived from diffusion tensor such as anisotrophy indexes are
used to evaluate white matter diseases in Krabbe’s disease, cerebral
adrenoleukodystrophy,
AIDS,
multiple
sclerosis,
hypertensive
encephalopathy, age related changes, schizophrenia, alzheimer’s
disease, ischaemic leukoaraiosis and epilepsy.
 Properties derived from diffusion tensor like trace which reflects overall water
content can be used to evaluate brain ischaemia.
 Studies are also done on the potential of DTI in brain tumors, migraine,
eclampsia, functioning of transplant kidney and diffuse axonal injury.
Summary:
White matter tractography based on DTI is a rapidly evolving
technology in CNS imaging with many challenges and exiting new applications.
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This study has attempted to provide a concise pictorial review of major tract
anatomy typically visualized on directional DTI colour maps and average range
of normal FA, ADC values, fiber lines and tract length in our population though
they may not be representative values.
Thank you