Basic proton MR imaging
Tissue Signal Characteristics
Neuroimaging Primer,
Keith A. Johnson, M.D., Harvard Medical School
See also Signal Sources.
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 region of interest. The following is 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