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Diffusion-Tensor MR Imaging and Tractography at 3T:
Anatomy and Clinical Applications.
Poster No.:
C-0542
Congress:
ECR 2011
Type:
Educational Exhibit
Authors:
M. Recio , L. C. Hernández González , V. Martinez de Vega ,
1
2
1
1
1
1
M. Jimenez De La Peña , S. Gil Robles , J. Carrascoso Arranz ,
1
1
1 1
R. Cano Alonso , E. Alvarez , L. Herraiz Hidalgo ; Madrid/ES,
2
Oviedo/ES
Keywords:
Neuroradiology brain, MR-Diffusion/Perfusion, Diagnostic
procedure, Pathology
DOI:
10.1594/ecr2011/C-0542
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Learning objectives
We review the normal anatomy of the white matter (WM) tracts as they appear on
directional diffusion tensor imaging (DTI) color maps and tractography.
Anatomic gross dissection photographs are correlated with tractography to review the
anatomy of those tracts, which are readily seen in most cases.
We describe the principles of diffusion contrast and anisotropy, as well as their main
clinical applications in developmental abnormalities, demyelinating disease, ischemic
disease, infectious diseases, neurodegenerative disordes, neoplasms and preoperative
studies.
2
DTI MR images were obtained with a 3T system and b values of 0 and 1000 s/mm were
used. Our imaging protocol consisted of 82 diffusion encoding gradient directions when
comparing with anatomic sections from cadavers and 25 diffusion encoding gradient
directions when clinical applications were under evaluation.
Background
Diffusion magnetic resonance (MR) imaging is evolving into a potent tool in the
examination of the central nervous system. Although it is often used for the detection
of acute
ischemia, evaluation of directionality in a diffusion measurement can be useful in
white matter, which demonstrates strong diffusion anisotropy. Techniques such as
diffusion-tensor imaging offer a glimpse into brain microstructure at a scale that is
not easily accessible with other modalities, in some cases improving the detection
and characterization of white matter abnormalities. Diffusion MR tractography offers an
overall view of brain anatomy, including the degree of connectivity between different
regions of the brain.
Imaging findings OR Procedure details
Diffusion contrast is based on the self-diffusion of water molecules in tissue. Although
a variety of sequences are now used to acquire DW images, all DW sequences include
two equal and opposing motion-probing gradients. Diffusion is anisotropic (directionally
dependent) in WM fiber tracts, as axonal membranes and myelin sheaths represent
barriers to the motion of water molecules in directions not parallel to their own orientation.
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The direction of maximum diffusivity has been shown to coincide with the WM fiber tract
orientation . This information is contained in the diffusion tensor, a mathematic model
of diffusion in three-dimensional space. The tensor model of diffusion consists of a 3x3
matrix derived from diffusivity measurements in at least six noncollinear directions.
Fractional anisotropy (FA) is an index ranging from 0 (isotropic) to 1 (maximally
anisotropic)) The direction of maximum diffusivity may be mapped by using red, green,
and blue (RGB) color channels with color brightness modulated by FA, resulting in a
convenient summary map from which the degree of anisotropy and the local fiber direction
can be determined. The convention we used for directional RGB color mapping is red for
left-right, green for anteroposterior,and blue for superior-inferior. We employed b value of
b 0 and 1000 s/mm2 and 82 encoding gradient directions in the comparative study with
anatomic sections from cadavers , meanwhile 25 encoding gradient directions directions
were used when evaluating different clinical applications.
White matter tracts were estimated with tractography. Tracking was initiated from a
start location (or seed point) in both forward and backward directions. The ROIs were
chosen to enclose tract cross sections that were visible in any of the axial, sagittal, or
coronal directional color maps. Fiber trajectories are displayed with colors superimposed
on gray-scale anatomic images in various three dimensional projections. Note that,
unlike directional color maps in which directional information is color-coded, individual
tractograms are displayed by using fixed colors which are arbitrarily chosen.(Figure 1)
on page 9, (Figure 2) on page 10, (Figure 3) on page 11
WHITE MATTER FIBER CLASSIFICATION
• Association fibers interconnect cortical areas in each hemisphere. Association
fibers typically identified on DTI color maps include: cingulum, superior and inferior
occipitofrontal fasciculi, uncinate fasciculus, superior longitudinal (arcuate) fasciculus,
and inferior longitudinal (occipitotemporal) fasciculus.
• Projection fibers interconnect cortical areas with deep nuclei, brain stem, cerebellum,
and spinal cord. There are both efferent (corticofugal) projection fibers (cortico-spinal,
cortico-bulbar, and cortico-pontine) and afferent (corticopetal) projection fibers (medial
lemniscus; anterior, superior and posterior thalamic radiation; inferior spinocerebellar
fascicles or Flechsig's fasciculus, superior spinocerebellar fascicles or Gowers' tract and
optic radiation).
• Commissural fibers interconnect similar cortical areas between opposite hemispheres
(corpus callosum, anterior commissure, posterior commissure, interthalamic gray
commissure or intermediate mass and Psalterium or David ´s lyra).
ASSOCIATION FIBERS
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Cingulum:The cingulum begins in the parolfactory area of the cortex below the rostrum
of the corpus callosum, then courses within the cingulate gyrus, and, arching around
the entire corpus callosum, extends forward into the parahippocampal gyrus and uncus.
It interconnects portions of the frontal, parietal, and temporal lobes. Its arching course
over the corpus callosum resembles the palm of an open hand with fingertips wrapping
beneath the rostrum of the corpus callosum.
Superior Occipitofrontal Fasciculus: Whereas the cingulum wraps around the superior
aspect of the corpus callosum, the superior occipitofrontal fasciculus lies beneath it. It
connects occipital and frontal lobes, extending posteriorly along the dorsal border of the
caudate nucleus. Portions of the superior occipitofrontal fasciculus parallel the superior
longitudinal fasciculus but they are separated from the superior longitudinal fasciculus by
the corona radiata and internal capsule (Figure 4) on page 12.
Inferior Occipitofrontal Fasciculus: The inferior occipitofrontal fasciculus also
connects the occipital and frontal lobes but is far inferior compared with the superior
occipitofrontal fasciculus. It extends along the inferolateral edge of the claustrum, below
the insula. Posteriorly, the inferior occipitofrontal fasciculus joins the inferior longitudinal
fasciculus, the descending portion of the superior longitudinal fasciculus, and portions
of the geniculocalcarine tract to form most of the sagittal stratum, a large and complex
bundle that connects the occipital lobe to the rest of the brain. The middle portion of
the inferior occipitofrontal fasciculus is bundled together with the middle portion of the
uncinate fasciculus.
Uncinate Fasciculus Uncinate is from the Latin uncus meaning "hook." The uncinate
fasciculus hooks around the lateral fissure to connect the orbital and inferior frontal gyri
of the frontal lobe to the anterior temporal lobe. The anterior aspect of this relatively
short tract parallels, and lies just inferomedial to, the inferior occipitofrontal fasciculus. Its
midportion actually adjoins the middle part of the inferior occipitofrontal fasciculus before
heading inferolaterally into the anterior temporal lobe. (Figure 5) on page
Superior Longitudinal (arcuate) Fasciculus:The superior longitudinal fasciculus is a
massive bundle of association fibers that sweeps along the superior margin of the insula
in a great arc, gathering and shedding fibers along the way to connect frontal lobe cortex
to parietal, temporal, and occipital lobe cortices. The superior longitudinal fasciculus is
the largest association bundle. (Figure 6) on page 14
Inferior Longitudinal (occipitotemporal) Fasciculus: The inferior longitudinal
fasciculus: connects temporal and occipital lobe cortices. This tract traverses the length of
the temporal lobe and joins with the inferior occipitofrontal fasciculus, the inferior aspect
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of the superior longitudinal fasciculus, and the optic radiations to form much of the sagittal
stratum traversing the occipital lobe. (Figure 7) on page 15
PROJECTION FIBERS:
Corticospinal, Corticopontine, and Corticobulbar: The corticospinal and
corticobulbar tracts are major efferent projection fibers that connect motor cortex to the
brain stem and spinal cord. Corticospinal fibers converge into the corona radiata and
continue through the posterior limb of the internal capsule to the cerebral peduncle on
their way to the lateral funiculus. Corticobulbar fibers converge into the corona radiata
and continue through the genu of the internal capsule to the cerebral peduncle where
they lie medial and dorsal to the corticospinal fibers. Corticobulbar fibers predominantly
terminate at the cranial motor nuclei. (Figure 8) on page 16
The thalamic fibers (anterior, superior, and posterior thalamic radiations: The
anterior thalamic radiation interconnects anterior and medial thalamic nuclei with the
frontal lobe (Figure 9) on page 17; the superior thalamic radiation joins ventral group
of thalamic nuclei with the motor sensory areas and adjoining parts of frontal and
parietal lobes (Figure 10) on page 18.The posterior thalamic radiation joins occipital
and posterior parietal cortex with posterior thalamus including pulvinar; it includes optic
radiation from lateral geniculate body (Figure 11) on page 19.
Geniculocalcarine Tract (optic radiation):The optic radiation connects the lateral
geniculate nucleus to occipital (primary visual) cortex. The more inferior fibers of the optic
radiation sweep around the posterior horns of the lateral ventricles and terminate in the
calcarine cortex; the more superior fibers take a straighter, more direct path. The optic
radiation mingles with the inferior occipitofrontal
fasciculus, inferior longitudinal fasciculus, and inferior aspect of the superior longitudinal
fasciculus to form much of the sagittal stratum in the occipital lobe (Figure 12) on page
20.
Medial lemniscus: It is part of the posterior column-medial lemniscus system, which
transmits touch, vibration sense, as well as tthe pathway for propioception. Axons of
cells within nucleus gracilis and nucleu cuneatus cross as internal arcuate fibers and
form the medial lemniscus. The medial lemniscus carries axons from most of the body
and synapses in the ventral posterolateral nucleus of the thalamus , at the level of the
mamilary bodies. Sensory axons transmitting information from the head and neck via
the trigeminal nerve synapse at the ventral posteromedial nucleus of the thalamus. The
superior thalamic radiation connect the ventral posterolateral nucleus of the thalamus
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to the postcentral gyrus (somatosensory cortex) of the cerebral cortex (areas 3, 1, 2)
(Figure 13) on page 21.
Inferior spinocerebellar fascicles or Flechsig's fasciculus: The inferior
spinocerebellar tract conveys inconscient propioceptive information from the body to the
cerebellum. Proprioceptive information is taken to the spinal cord via central processes
of dorsal root ganglia (first order neurons). These central processes travel throughth the
dorsal horn where they synapse with second order neurons of Clarke's nucleus. Axon
fibers from Clarke's Nucleus convey this proprioceptive information in the spinal cord
in the peripheral region of the posteriolateral funiculus ipsilaterally until it reaches the
cerebellum, where unconscious proprioceptive information is processed.
Superior spinocerebellar fascicles or Gowers' tract: The superior spinocerebellar
tract conveys propioceptive information from the body to the cerebellum. Originates from
ventral horn at lumbosacral spinal levels. Axons first cross midline in the spinal cord and
run in the ventral border of the lateral funiculi. These axons ascend up to the pons where
they join the superior cerebellar peduncle to enter the cerebellum.
Middle cerebellar peduncles: The largest of the three paired peduncles, composed
mainly of fibers that originate from the pontine nuclei, cross the midline in the basilar part
of the pons, and emerge on the opposite side as a massive bundle arching dorsally along
the lateral side of the pontine tegmentum into the cerebellum. Via this connection, the
cerebellum receives a copy of the information for muscle movement that the pyramidal
tract is carrying down to lower motor neurons (Figure 14) on page 22.
COMMISSURAL FIBERS:
Corpus Callosum: By far the largest WM fiber bundle, the corpus callosum is a
massive accumulation of fibers connecting corresponding areas of cortex between the
hemispheres. Fibers traversing the callosal body are transversely oriented, whereas
those traversing the genu and splenium arch anteriorly and posteriorly to reach the
anterior and posterior poles of the hemispheres (Figure 15). on page 23
Anterior Commissure: The anterior commissure crosses through the lamina terminalis.
Its anterior fibers connect the olfactory bulbs and nuclei; its posterior fibers connect
middle and inferior temporal gyri.
Posterior Commissure: The posterior commissure (also known as the epithalamic
commissure) is a rounded band of white fibers crossing the middle line on the dorsal
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aspect of the upper end of the cerebral aqueduct. It is important in the bilateral pupillary
light reflex.
Interthalamic gray commissure or intermediate mass: The medial surface of the
thalamus constitutes the upper part of the lateral wall of the third ventricle, and is
connected to the corresponding surface of the opposite thalamus by a flattened gray
band, the Interthalamic adhesion.
Psalterium or David ´s lyra: The lateral portions of the body of the fornix are joined
by a thin triangular lamina, named the psalterium (lyra). This lamina contains some
transverse fibers that connect the two hipoccampi across the middle line and constitute
the commissure of fornix (hippocampal commissure) (Figure 16) on page 24.
ROM A FUNCTIONAL STANDPOINT THE MOST IMPORTANT FASCICULUS ARE:
- Pyramidal tract (motor studies).
- Medial lemniscus and superior corona radiata (sensory studies).
- Meyer´s loop and optical radiations (visual studies).
- Arcuate and inferior frontooccipital fasciculilanguage assessment): Arcuate
fasciculus lesions cause paraphasia phonetics (conduction aphasia) and inferior
longitudinal fasciculus lesions cause semantic paraphasias.
CLINICAL APPLICATIONS :
There are many pathological processes that affect anisotropic diffusion. The main
clinical applications are:
Myelination process: In premature newborns, increased anisotropy is found in
developing cortical gray matter rather than in unmyelinated white matter, and cortical
anisotropy steadily decreases during the first few months of life. DTI can assess the
process of myelination.
Developmental brain disorders: DT I allows the study of abnormal interhemispheric
connections in cases of complete or partial agenesis of the corpus callosum. In
lissencephaly, tractography of the grossly abnormal subcortical and deep white matter
has demonstrated an incomplete development of the fornix and cingulate tracts. In
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cases of alobar holoprosencephaly , absence of corticospinal tracts have been observed
by means of DTI . Many white matter tract structures, such as the middle cerebellar
peduncles, were found to be smaller in alobar holoprosencephaly than in semilobar or
lobar holoprosencephaly. Furthermore, the size of the corticospinal tracts and middle
cerebellar peduncles in all three variants was found to correlate with neurodevelopmental
status. Joubert syndrome shows aberrant connections in abnormal superior cerebellar
peduncles (Figure 17) on page 25.
Demyelinating disease: Diffusion tensor is an effective tool in the assessment of white
matter involvement, specially for the purposes of quanting the anisotropy and to perform
to follow up studies in patients with multiple sclerosis. DTI imaging allows to control the
degree of cortico-spinal tract involvement (Figure 18) on page 26 (Figure 19) on page
27. on page 26
Hypoxic ischemic disease: Tractography is useful in assessing both the integrity
of the different fibers in the ischemic area and prognosis: We use it to establish a
prognosis in children with congenital hemiparesis valuing the FA in the cortico-spinal
tract. Thus a decrease <3% suggests mild hemiparesis, decreased values ranging from
18%-46% suggest moderate hemiparesis , and values higher than 47% suggest severe
hemiparesis. In cases of cystic cavities of encephalomalacia or porencephalic. wallerian
degeneration occurs, after stroke, there is a decrease in FA values (Figure 20) on page
28 (Figure 21) on page 29 on page 28 (Figure 22). on page 30
on page 28
Infectious diseases: Encephalitis, particularly herpetic encephalitis causes marked
impairment of cortical and white matter with involvement of temporal lobes, limbic system
and insular region . affecting inferior fronto-occipital fasciculus ,uncinate fasciculus,
inferior longitudinal fasciculus and cingulum (Figure 23). on page 31
Degenerative disease: Parkinson's disease presents reduced FA in the substantia nigra
with normal anisotropy in caudate and putamen. lncreased diffusivity and decreased
anisotropy were found in the corpus callosum and the frontal, temporal, and parietal white
matter in both patients with Alzheimer disease and those with Lewy body dementia, but
the occipital lobes were involved only in the latter. Multiple groups have demonstrated
decreased anisotropy and increased diffusivity in the internal capsule and cerebral
peduncles of patients with amyotrophic lateral sclerosis . In multisystemic atrophy
(MSA) we can detect the degree of involvement of the middle cerebellar peduncles and
brainstem (Figure 24) on page 32.
Tumors: The goal of surgical treatment for cerebral neoplasms is to maximize the
extent of tumor resection while minimizing postoperative neurologic deficits resulting from
damage to intact, functioning brain. This requires preoperative or intraoperative mapping
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of the tumor and its relationship to functional structures, including cerebral cortex and
WM tracts. Cortical mapping can be accomplished with either functional MR imaging or
intraoperative electrocortical stimulation (Figure 25) on page 33 (Figure 26) on page
34 (Figure 27) on page 35 (Figure 28) on page 36 (Figure 29) on page 37
(Figure 30) on page 38 (Figure 31) on page 39 .
Preoperative mapping of vascular disease: Surgery of cavernomas is the most
common vascular indication (Figure 32) on page 40 (Figure 33) on page 41 .
Epilepsy: Tractography is particularly usefull in the assesment of surgical aproach,
specially in resections close to Broca and Wernicke areas, as is capable of assessing
the integrity of the arcuate and inferior frontooccipital fasciculus. It also allows studying
the integrity of optical radiation and Meyer loop in order to prevent visual field defects
(figure 34) on page 42.
Phychiatric disorders: Various disorders such as attention deficit disorder in obsessive
compulsive disorders, autism or schizophrenia show decreased FA in specific locations.
Images for this section:
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Fig. 1: Abbreviations: ACR anterior region of corona radiata, ALIC anterior limb of internal
capsule, AF arcuate fasciculus , BCC body of corpus callosum, CBT corticobulbar tract,
CG cingulum, CP cerebral peduncle, CST corticospinal tract, DN dentate nucleus, DSCP
decussation of superior cerebellar peduncle, GCC genu of corpus callosum, ICP inferior
cerebellar peduncle, IFO inferior fronto-occipital fasciculus, ILF inferior longitudinal
fasciculus, MCP middle cerebellar peduncle, ML medial lemniscus, OR optic radiation,
PCR posterior region of corona radiata, PLIC posterior limb of internal capsule, PTR
posterior thalamic radiations, SCC splenium of corpus callosum, SCR superior region
of corona radiata, SFO superior fronto-occipital fasciculus, SLF superior longitudinal
fasciculus, SN substantia nigra, SRAF short-range association fibers, T tapetum, UF
uncinate fasciculus and VOF vertical occipital fasciculus.
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Fig. 2: Abbreviations: ACR anterior region of corona radiata, ALIC anterior limb of internal
capsule, AF arcuate fasciculus , BCC body of corpus callosum, CBT corticobulbar tract,
CG cingulum, CP cerebral peduncle, CST corticospinal tract, DN dentate nucleus, DSCP
decussation of superior cerebellar peduncle, GCC genu of corpus callosum, ICP inferior
cerebellar peduncle, IFO inferior fronto-occipital fasciculus, ILF inferior longitudinal
fasciculus, MCP middle cerebellar peduncle, ML medial lemniscus, OR optic radiation,
PCR posterior region of corona radiata, PLIC posterior limb of internal capsule, PTR
posterior thalamic radiations, SCC splenium of corpus callosum, SCR superior region
of corona radiata, SFO superior fronto-occipital fasciculus, SLF superior longitudinal
fasciculus, SN substantia nigra, SRAF short-range association fibers, T tapetum, UF
uncinate fasciculus and VOF vertical occipital fasciculus.
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Fig. 3: Abbreviations: ACR anterior region of corona radiata, ALIC anterior limb of internal
capsule, AF arcuate fasciculus , BCC body of corpus callosum, CBT corticobulbar tract,
CG cingulum, CP cerebral peduncle, CST corticospinal tract, DN dentate nucleus, DSCP
decussation of superior cerebellar peduncle, GCC genu of corpus callosum, ICP inferior
cerebellar peduncle, IFO inferior fronto-occipital fasciculus, ILF inferior longitudinal
fasciculus, MCP middle cerebellar peduncle, ML medial lemniscus, OR optic radiation,
PCR posterior region of corona radiata, PLIC posterior limb of internal capsule, PTR
posterior thalamic radiations, SCC splenium of corpus callosum, SCR superior region
of corona radiata, SFO superior fronto-occipital fasciculus, SLF superior longitudinal
fasciculus, SN substantia nigra, SRAF short-range association fibers, T tapetum, UF
uncinate fasciculus and VOF vertical occipital fasciculus.
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Fig. 14: Figure 14
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Fig. 24: Figure 24
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Fig. 25: Figure 25
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Fig. 26: Figure 26
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Fig. 27: Figure 27
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Fig. 32: Figure 32
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Fig. 33: Figure 33
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Fig. 34: Figure 34
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Conclusion
• Diffusion tensor imaging and tractography are a key tool in the anatomical study of
white matter fibers and projection, association and commissural fibers that improves
conventional magnetic resonance imaging.
• Diffusion tensor imaging is able to show abnormalities in a wide variety of diseases
such as developmental disorders or psychiatric disorders and is specially useful in the
assessment of ischemic disease, multiple sclerosis and tumors.
• The use of tensor imaging in conjunction with functional studies (motor, visual, speech or
memory), cortical mapping and intraoperative stimulation is a promising trend that helps
prevent surgical neural damage.
Personal Information
Dr. Manuel Recio Rodríguez.
Hospital Quirón Madrid.
[email protected]
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