Want to learn more about how to read a brain MRI?  Here are the basics:

• MRIs are described by signal intensity, as compared to CTs where lesions are described by density.
  • A dark lesion on MRI is “hypointense”
  • A bright lesion on MRI is “hyperintense"
• The most commonly used MRI sequences are T1-weighted, T2-weighted, FLAIR, and Diffusion-weighted.
  • T1-weighted images are good for brain parenchyma.
    • Contrast enhanced T1 with gadolinium helps differentiate pathological tissue (e.g. tumors, inflammation, infection)
  • T2-weighted images are good for CSF spaces and periventricular white matter.
    • Edema from a tumor, subacute stroke or hemorrhage appears bright
    • Periventricular white matter scarring from multiple sclerosis appears bright
  • FLAIR images are T2 images where CSF is dark.  FLAIR is very sensitive to edema and parenchymal lesions.
  • Diffusion-weighted sequences are good for cellular swelling.
    • Acute ischemia appears bright on Diffusion-Weighted Imaging (DWI) and dark on Apparent Diffusion Coefficient (ADC) maps
    • Some neoplasms, abscesses and toxic/metabolic/demyelinating processes can also appear bright on DWI.

Stay tuned for more pearls in this series on brain MRI!

References

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