MRI sequences [advanced]

T1 and T2 weighted

• T1 vs T2 difference:

• 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)