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T2 Decay Curve
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Mxy = Mø * e-t/T2
| -t/T2 |
Mxy |
| -0.5 |
0.607 |
| -1 |
0.368 |
| -2 |
0.135 |
| -3 |
0.050 |
| -4 |
0.018 |
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Similar to T1 relaxation, the signal decay resulting from transverse or spin-spin relaxation is described mathematically by an exponential curve, identical in concept to radioactive decay with a half-life measured in tens of msecs. The value T2 is the time after excitation when the signal amplitude has been reduced to 36.8% of its original value (or has lost 63.2%. - This is the opposite of T1 where 63.2% of Mz is recovered in one T1 period.) The value of T2 is unique for every kind of tissue and is determined primarily by its chemical environment with little relation to field strength. In chapter 5, we will discuss in more detail how these unique T2 values are used to produce different types of image contrast.
T2 Decay: The exponential loss of signal resulting from purely random spin-spin interactions in the transverse or XY plane.
 In general, T2 values are unrelated to field strengths (unlike T1 values).
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