Download Susceptibility Weighted Imaging (SWI): Contributions to Multiple

Susceptibility Weighted Imaging (SWI): Contributions to
Multiple Sclerosis
Poster No.:
C-1019
Congress:
ECR 2015
Type:
Educational Exhibit
Authors:
R. M. Ruiz Peralbo, B. Brea Alvarez, M. Alfageme Zubillaga,
C. Perez Martin, C. Gonzalez Hernando, I. Rivera Campos, A.
M. Alcolado Jaramillo, C. De la Rosa Ruiz, L. Esteban Garcia;
Majadahonda/ES
Keywords:
Tissue characterisation, Imaging sequences, MR, Neuroradiology
brain
DOI:
10.1594/ecr2015/C-1019
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Learning objectives
Usual MRI sequences used in studies of multiple sclerosis allow detection of lesions both
in diagnosis and in the monitoring of disease.
Susceptibility weighted imaging (SWI) is a relatively recent sequence with high
sensitivity in the detection of paramagnetic substances: hemosiderin, calcium and
deoxyhemoglobin.
This feature, in the case of multiple sclerosis, can see the relationship between the
plaques in white matter and venular structures and the association of lesions with different
patterns of iron deposition.
Background
Multiple sclerosis is the most common neurological disease of young adult caucasian
and the most common cause of neurological disability in young adults.
It is an inflammatory and demyelinating disease characterized by inflammation,
demyelination plaques, axonal loss and gliosis.
MRI is nowadays a mainstay in the diagnosis and monitoring of multiple sclerosis.
Diagnostic criteria proposed by McDonald et al. (revised 2010) give great importance to
the findings of MRI studies with the presence of CNS demyelinating lesions scattered in
space and time.
Sensitivity in the diagnosis of multiple sclerosis using classical protocols with MRI
sequences (T2, FLAIR, DP, T1 after gadolinium) is very high, but there are nonspecific
findings that can be misinterpreted and lead to false positives with a overestimation in
the diagnosis of disease. (1)
SWI can increase the specificity of these confusing cases.
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Findings and procedure details
It could increase the specificity of the cases more dubious for a diagnosis of multiple
sclerosis getting greater detail some of the typical features of lesions of multiple
sclerosis as: location (perivenular), distribution (periventricular) and morphology (ovoid
form ,perpendicular to ventricles: Dawson's fingers).
In that sense, SWI is an additional sequence providing complementary information to that
obtained with conventional sequences in terms of these characteristics.
SWI provides a detailed anatomical information of the cerebral venous system, in which
the veins are hypointense structures.
Typical distribution of multiple sclerosis plaques is associated with perivenular location,
which can be viewed by SWI. Venular blood supply is abundant in: periventricular deep
white matter (Dawson's fingers) and in the ependymal surface of corpus callosum, so
typically, but not specifically, multiple sclerosis lesions are distributed in the interface of
corpus callosum unlike in the lesions of another etiologies that affect the entire thickness
of corpus callosum (fig1, fig2, fig3).
Dawson fingers, finding typical of multiple sclerosis are the morphological expression
of perivenular inflammation around venules extending perpendicular to the ventricular
surface. (fig3).
In cases with nonspecific lesions especially located in deep subcortical white matter,
without distribution and location so typical of multiple sclerosis, SWI can delimit venules
anatomically and detect lesions with perivenular distribution, such that the identification
of the venule within problem lesion can help to catalog this lesion as injury multiple
sclerosis (fig 3, fig 5) against other lesions in the white matter of another etiology without
perivenular relationship (fig 6).
So the visibility of the central vein could be a discriminant score among the white matter
lesions of multiple sclerosis of non-multiple sclerosis injuries (2).The central vein within
the lesion is identified at 3T with SWI at least 45% of the lesions of multiple sclerosis
compared to 8% of the incidental white matter lesions (3).
It is already known the relationship between iron deposits in gray and white matter of
the brain parenchyma and the aging and neurodegenerative diseases, such as multiple
sclerosis.
During the first four weeks of the inflammatory process, the activity in the lesions of
multiple sclerosis is expressed with an enhancement in open ring after administration
of gadolinium, as expression of the interruption of the blood brain barrier, during which
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extravasation occurs red blood cells,that are kidnapped by microglia cells and whose
products metabolic degradation are detected as hypointense signals in sequence SWI.
The detection of those iron deposits by SWI is possible because of is capable
discriminating subtle changes in susceptibility between areas with degradation products
of the blood and surrounding cerebral tissue.
Those iron deposits detected by SWI within T2 hyperintense lesions no longer enhanced
after administration of gadolinium act as witnesses of an prior inflammatory episode. So
SWI allows identification of hypointense signals within the lesions of multiple sclerosis
(intralesional signal susceptibility) that have not been identified in white matter lesions
of other etiologies and translate as extravasation of erythrocytes through the blood brain
barrier.(4)
Moreover, the morphology and arrangement of the iron deposits in white matter of MS
injuries detected by SWI adopt a characteristic pattern "in border" (fig11) , following the
edges delimiting the previous enhancement of this lesion ( as a result of accumulation
of the products degradation of extravasated red blood cells through interruption of the
blood brain barrier during inflammatory process) opposite the patterns of iron deposit of
another pathologies (fig 14, fig 15).
SWI is a sequence in T2 weighted ,3D ,high resolution and a post-processing applied.
SWI is a particularly sensitive in detecting of paramagnetic substances, than in the
brain are represented mainly by iron , bound to heme, deoxyhemoglobin and products
derived from the destruction of the same. So all those tissues in which those components
are involved may be detected with higher sensitivity by this sequence. Compared to
T2* sequence presenting better discrimination between tissues paramagnetic and no
paramagnetic.
Estimated time to obtain all brain coverage is 3 to 5 minutes, which are used in the
signal acquisition and remove incidental phase variations due to non homogeneous static
magnetic fields, a process that is automatically achieved by the system providing 3D
images .The phase image (previously filtered with a mask) is multiplied to the magnitude
image to improve visualization of microvessels. Finally, minIP reconstruction is performed
with selected thickness (1-2 cm) generating images to contrast all the hypointense
signals produced by the different tissue susceptibility to find hemorrhage, calcium, iron
deposits ...
As limitations of the sequence, we can mention that despite having very good sensitivity,
has enough noise that can limit the anatomic location, the quality of the image is
relatively poor in areas that are close to the skull base and although provides a detailed
identification of the cerebral venous system, it is not good for the superior sagittal sinus
venosus.
Page 4 of 22
At present, its main applications include studies of vascular malformations (cavernomas),
chronic vasculopathy and future applications are investigated in neoplastic disease and
in multiple sclerosis.
Images for this section:
Fig. 1: FLAIR sagittal : Involvement of the ependymal surface of the corpus callosum
showing hyperintense signal in male patient aged 40 diagnosed with multiple sclerosis.
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Fig. 2: FLAIR sagittal : Involvement of the ependymal surface of the corpus callosum
showing hyperintense signal in the same patient who is referred in fig.1.
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Fig. 3: SWI sagittal : Perivenular distribution of the lesion which is referred in fig.1.
Correlating lesion of the corpus callosum ependymal surface in FLAIR sagittal with SWI
sagittal showing perivenular distribution of the lesion : venulas as hypointense structures
linear perpendicular to the ventricular surface.
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Fig. 4: T2 coronal: Hyperintense injury in periventricular white matter. 43 year old woman
with diagnosis MS.
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Fig. 5: SWI coronal : Detail of structure venular within white matter lesion periventricular
white as hyperintense T2 signal of the patient who is referred in Fig.4.
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Fig. 6: SWI axial: Locator value of SWI, identifying venular structures in a patient with
multiple perivascular Virchow-Robin spaces shown as hypointense signals with linear
morphology, which are hyperintense in T2 of Fig7.
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Fig. 7: T2 axial: Perivascular spaces which are referred in Fig. 6 (red arrow).
Hyperintense injury in deep subcortical white matter of the left hemisphere (blue arrow)
in a patient with known chronic ischemic lesions, in this case, is not distributed as
perivenular (No structure as venule is identified within this lesion, probably of ischemic
etiology, in SWI in fig.6)
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Fig. 8: FLAIR axial: Hyperintense juxtacortical left anterior frontal injury in male patient
aged 44 diagnosed of multiple sclerosis.
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Fig. 9: Detail of the left anterior frontal lesion yuxtacortical which is referred in Fig. 8.
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Fig. 10: FLAIR coronal: Cortical atrophy predominantly in the left hemisphere in the
patient who is referred to in fig8 and fig9.
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Fig. 11: SWI axial: Characteristic pattern of iron deposit of multiple sclerosis, showing
hypointense signals, are grouped around the edge, perfectly defined, of the lesion
described in fig 8 and fig 9.
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Fig. 12: T2 axial: Several lesions in deep subcortical white matter of both hemispheres.
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Fig. 13: FLAIR axial: Involvement of periventricular white matter and brain atrophy
associated in the patient who is referred in Fig12.
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Fig. 14: SWI axial : Findings described in fig 12 and fig 13 are nonspecific and may be
shared by several diseases, including MS. SWI in fig 14 and fig 15 shows a pattern of iron
deposit, which in this case is not characteristic of multiple sclerosis, with the presence of
multiple and small hypointense signals of anarchic distribution suggestive of vasculitis.
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Fig. 15: SWI axial: Cranial plane to referred in fig14 showing lot of punctate iron deposits
in patient with diagnosis of vasculitis.
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Conclusion
SWI is an additional sequence ,that together to usual MRI sequences, helps to
characterize the white matter lesions detected by the conventional protocol, in multiple
sclerosis diagnosis ,providing an additional valuable information for the diagnosis of
CNS pathology, particularly for debugging the differential diagnosis of lesions of multiple
sclerosis respect to other lesions of white matter nonspecific , especially in subcortical
distribution.
Offers interesting insights for understanding the pathophysiology of this disease, and the
basis for future research.
It could be useful as predictive early marker of inability to identify abnormal iron deposits,
which are the first step in the development of neurodegenerative diseases, such as
multiple sclerosis.
Personal information
[email protected]
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