CNS Imaging Basics

MRI Basics

MRI Sequences

Sequence Fat CSF Edema and Demyelination
T1 Bright Dark Sl. Dark
T2 Dark Bright Sl. Bright
FLAIR Dark Dark Bright
  • Fat has larger longitudinal and transverse magnetization and will appear bright on T1 imaging. water has less longitudinal magnetization prior to a RF pulse, therefore less transverse magnetization after a RF pulse yielding low signal appearing dark on a T1 contrast image.
  • Water has a very high T2 constant, therefore has very high T2 signal. Also, since the amount of transverse magnetization in fat is small, fat generates very little signal on a strong T2 weighted contrast image and appears intermediate to dark.
  • FLAIR is T2 image with pure H2O suppression. Edema-generating pathology and white matter lesions, including demyelinating processes, are especially highlighted with FLAIR
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