UMEM Educational Pearls

Title: Shades of Gray Matter - Brain MRI 101

Category: Neurology

Keywords: magnetic resonance imaging, MRI, T1, T2, FLAIR, DWI, ADC (PubMed Search)

Posted: 5/11/2016 by WanTsu Wendy Chang, MD
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Shades of Gray Matter - Brain MRI 101

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!

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