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MRI sequences [advanced]

T1 and T2 weighted

  • T1 vs T2 difference:

On T2, H2O (including CSF) = bright
Includes oedema which signifies disease

  • Bright on both = fat
  • Grey on both = soft tissues
  • Black on both = bone, air, flowing blood

Gadolinium-enhanced

Same as T1 but…

  • Gadolinium, a contrast agent, is given
  • Enhances areas of leaky blood vessels (pathological tissues e.g. tumours, areas of inflammation/infection)

Fluid-attenuated (FLAIR)

Same as T2 but…

  • Flowing water (like CSF) is supressed, so appears black
  • Only non-flowing water appears bright
  • Helps differentiate pathologic oedematous lesions from normal flowing water (like CSF)

Fat-supressed

  • Fat supressed T1 or T2
  • Used to make fat appear dark
  • Often used when giving gadolinium contrast on T1, or on T2 to allow fluid to stand out

Diffusion-weighted image (DWI)

  • Shows passive diffusion of water
  • Consists of two main images:
    • DWI – combination of actual diffusion and T2 (restricted diffusion = bright)
    • ADC – represents actual diffusion without T2 effects (restricted diffusion = dark)
  • Cytotoxic oedema = bright on DWI and dark on ADC
  • Most useful when looking for ischaemic brain tissue in stroke
  • Note, DWI is derived from T2; therefore, some tissues that are bright on T2 also appear bright on DWI (T2 shine through effect)
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