About Multiple Sclerosis
Multiple Sclerosis (MS) is a chronic, immune-mediated, inflammatory disease of the Central Nervous System (CNS) that causes demyelination of axonal myelin sheaths and neurodegeneration. The peak onset is between age 20 and 40 years and women are affected approximately twice as often as men. Patients with MS suffer from a variety of neurological symptoms.
Four disease courses have been identified in multiple sclerosis:
clinically isolated syndrome (CIS)
relapsing-remitting MS (RRMS)
primary progressive MS (PPMS)
secondary progressive MS (SPMS)
Although multiple sclerosis is primarily a white matter disease, grey matter can also be affected.
Magnetic Resonance Imaging (MRI) is a valuable diagnostic tool that is capable of showing demyelinating lesions in the brain and monitoring their evolution (fig. 1).
Fig. 1 MRI is very useful at the follow-up step, in patients with established MS. Upper row shows 3D FLAIR in sagittal (A), coronal (B) and axial (C) plane. Lower row shows 3D FLAIR in sagittal (D), coronal (E) and axial (F) plane. Lower row MR images (D, E, F) have been obtained six (6) months later compared to upper row's. Disease progression can clearly be seen in the form of new lesions in pons. Image courtesy of Bac Nguyen.
There are a lot of pulse sequences that can be used in MRI of multiple sclerosis, each offering different aspects of disease’s complex pathophysiology. The analysis of advanced and quantitative MR Imaging techniques (e.g. PWI, DWI, DTI, in-vivo MRS) is outside the scope of this review.
Fluid Attenuated Inversion Recovery (FLAIR):
FLAIR is one of the most important sequences for MS detection and evaluation, because of its high sensitivity. FLAIR pulse sequence uses an inversion recovery pulse (180°) to selectively suppress the signal from the cerebrospinal fluid (CSF) (fig. 2). Inversion time (TI) should be selected in the range of 1700-2500 msec (TI selection depends on the field strength and manufacturer). White matter lesions ("T2 lesions") are depicted as focal areas of hyperintensity ("bright spots"), reflecting different levels of myelin loss, inflammatory activity and gliosis (fig. 3). FLAIR imaging provides very high sensitivity in the depiction of hyperintense T2 lesions close to the CSF, such as the juxtacortical and the periventricular white matter, but is less sensitive in the posterior fossa, cortex and grey matter (fig. 4).
Fig. 2 FLAIR sequence timing diagram. FLAIR pulse sequence uses an inversion recovery pulse (180°) to selectively suppress the signal from the CSF. Inversion time (TI) should be selected in the range of 1700-2500 msec, depending on the field strength and vendor.
Fig. 3 3D sagittal FLAIR (A), multiplanar reconstruction in coronal plane (B) and axial 2D FLAIR (C). MS lesions are depicted as focal areas of hyperintensity ("T2 lesions").
Fig. 4 3D sagittal FLAIR (A) and multiplanar reconstruction in coronal (B) and axial (C) plane. 3D sagittal DIR (D) and multiplanar reconstruction in coronal (E) and axial (F) plane. DIR sequence is very useful in depicting cortical grey matter lesions (red circle), which are not well visible on FLAIR sequence. Image courtesy of Bac Nguyen.
Double Inversion Recovery (DIR):
DIR is a recent sequence, which attenuates the CSF as well as the white matter, providing a superior delineation between grey and white matter and enhancing any inflammatory lesion. Two inversion recovery pulses are required to obtain DIR sequence. TI1is used for the suppression of the CSF and TI2is used for the suppression of the white matter.
TI1 should be obtained at 1700-3500 msec, while TI2at 320-450 msec (the selection of the inversion times basically relies on the