Background:
Susceptibility-weighted imaging (SWI) is an iron-sensitive magnetic
resonance imaging (MRI) method that has shown iron-related
lesions in multiple sclerosis (MS) patients. The
contribution of deoxyhaemoglobin to the signals seen in SWI has not been
well
characterized in MS.
Objectives: To
determine if SWI lesions (seen as focal hypointensities) exist in the
experimental autoimmune encephalomyelitis (EAE)
animal model of MS, and to determine whether the
lesions relate to iron deposits, inflammation, demyelination, and/or
deoxyhaemoglobin
in the vasculature.
Methods: We performed
SWI on the lumbar spinal cord and cerebellum of EAE and control mice
(both complete Freund’s adjuvant/pertussis
toxin (CFA/PTX)-immunized and naive). We also
performed SWI on mice before and after perfusion (to remove blood from
vessels).
SWI lesions were counted and their locations
were compared to histology for iron, myelin and inflammation.
Results: SWI lesions
were found to exist in the EAE model. Many lesions seen by SWI were not
present after perfusion, especially at
the grey/white matter boundary of the lumbar
spinal cord and in the cerebellum, indicating that these lesion signals
were
associated with deoxyhaemoglobin present in the
lumen of vessels. We also observed SWI lesions in the white matter of
the lumbar
spinal cord that corresponded to iron
deposition, inflammation and demyelination. In the cerebellum, SWI
lesions were present
in white matter tracts, where we found
histological evidence of inflammatory perivascular cuffs.
Conclusions: SWI
lesions exist in EAE mice. Many lesions seen in SWI were a result of
deoxyhaemoglobin in the blood, and so may indicate
areas of hypoxia. A smaller number of SWI
lesions coincided with parenchymal iron, demyelination, and/or
inflammation.
Susceptibility weighted imaging (SWI), originally called BOLD venographic imaging, uses a type of contrast in magnetic resonance imaging (MRI) different from traditional spin density, T1, or T2 imaging. SWI uses a fully flow compensated, long echo, gradient echo (GRE) scan to acquire images. This method exploits the susceptibility differences between tissues and uses the phase image to detect these differences. The magnitude and phase data are combined to produce an enhanced contrast magnitude image which is exquisitely sensitive to venous blood, hemorrhage and iron storage. The imaging of venous blood with SWI is a blood-oxygen-level dependent (BOLD) technique which is why it was (and is sometimes still) referred to as BOLD venography. There is apparent iron deposition in EAE and hypoxia in animals which have not got CCSVI. maybe as occurs in MS