|Often used to indicate an image where most of the contrast between tissues or tissue states is due to differences in tissue T2 created typically by using longer TE and TR times.|
This term may be misleading in that the potentially important effects of tissue density differences and the range of tissue T2 values are often ignored.
Choosing the machine parameters such that TR greater than T1 (typically │ 2 000 ms) and TE less than T2 (typically │ 100 ms) and noting that (1-exp(-TR/T1) = 1 for TR/T1 much greater than 1, will reduce Eq. 1 to the expression
Mxy = Mxy0exp(-TE/T2)
which is dependent on T2 only, hence the term T2 weighting.
Therefore T2 weighted image contrast state is approached by imaging with a TR long compared to tissue T1 (to reduce T1 contribution to image contrast) and a TE between the longest and shortest tissue T2s of interest. A TR greater than 3 times the longest T1 is required for the T1 effect to be less than 5%. Due to the wide range of T1 and T2 and tissue density values that can be found in the body, an image that is T2 weighted for some tissues may not be so for others.
See also T2 Time.
Lesions with short T2 are (dark in T2 weighted sequences):
acute haemorrhage (deoxyHb)
physiologic iron (basal ganglia, etc.)
• View the DATABASE results for 'T2 Weighted' (46).
• View the NEWS results for 'T2 Weighted' (1).