Q. Which MR technique may
be used to discern otherwise occult Multiple sclerosis disease in
normal-appearing brain parenchyma?
a.MR spectroscopy
b.MT techniques
c. Diffusion-weighted MR imaging
d.T2W
e.T1W
ANS--.----b
MT techniques have been applied to
brain MR in an attempt to characterize MS lesions and to discern otherwise occult disease in normal-appearing brain parenchyma.
This pulse sequence technique
exploits differences in relaxation between immobilized water transiently bound
to macromolecules and water protons not associated with macromolecules. The
hypothesis underlying these investigations is that demyelination results in
more free water (i.e., a reduction in the “bound” fraction of water) compared
with myelinated white matter or intact but edematous tissue. Selective
suppression of immobilized water is accomplished by the application of an
off-resonance saturation pulse, which saturates the broad resonance of protons
bound to macromolecules. Transiently bound protons exchange with free water
protons by diffusion
Using experimental design, it has been shown in some
studies that MT ratios are higher (i.e., there is more signal reduction due to
the saturation pulse) in normal mature (myelinated) white matter than in gray
matter. A slight decrease of the magnetization transfer ratio was noted in
early inflammatory lesions without demyelination in models of experimental
allergic encephalomyelitis. More pronounced reductions in MT ratios have been
described in demyelinating lesions in experimental models (proportional to the
degree of demyelination) and in patients with MS
