If TR is short and if tissue A has a longer T1 than tissue B, the longitudinal magnetization of tissue A will recover less than the longitudinal magnetization of tissue B.
Thus, the transverse magnetization amplitude of tissue B will be higher after the next excitation.

 

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In the graphs below :

  • The first part of the following curves corresponds to the longitudinal magnetization recovery after the first excitation.
  • TR is the delay between excitations.
  • The second part corresponds to the transverse magnetization decay after the second excitation.
  • The MR signal is acquired at time TE after excitation.

 

By setting the TR to short values, tissue contrast will depend on differences in longitudinal magnetization recovery (T1).

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