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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.
- T1-weighted images are good for brain parenchyma.
Stay tuned for more pearls in this series on brain MRI!
References
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