Given: T_{2} = 100ms.

The relationship between the initial transverse magnetization (M_{xyo})
and the transverse magnetization at any time t, M_{xy}(t), is:

M

When the transverse magnetization (M_{xy}) has decayed to
37% of its starting value:

0.37 = e^{-t/T2}

ln( 0.37 ) = -t/T2

-T_{2} * ln( 0.37 ) = t

-100ms * ln( 0.37 ) = **99.4ms = t**