Signal in MR images is high or low (bright or dark), depending on the pulse sequence used, and the type of tissue in the image. The following tables are a general guide to how tissue appears on T1- or T2- weighted images.
Dark on T1-weighted image:
- increased water, as in edema, tumor, infarction, inflammation, infection, hemorrhage (hyperacute or chronic)
- low proton density, calcification
- flow void
Bright on T1-weighted image:
- fat
- subacute hemorrhage
- melanin
- protein-rich fluid
- slowly flowing blood
- paramagnetic substances: gadolinium, manganese, copper
- calcification (rarely)
- laminar necrosis of cerebral infarction
Bright on T2-weighted image:
- increased water, as in edema, tumor, infarction, inflammation, infection, subdural collection
- methemoglobin (extracellular) in subacute hemorrhage
Dark on T2- weighted image:
- low proton density, calcification, fibrous tissue
- paramagnetic substances: deoxyhemoglobin, methemoglobin (intracellular), iron, ferritin, hemosiderin, melanin
- protein-rich fluid
- flow void
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