纵向弛豫是指90°射频脉冲结束后（ ）The longitudinal relaxation refers to （ ） after the end of the 90 ° RF pulse

A、Mxy由小变大的过程TheprocessofMxyincreasingtothemaximum;
B、Mxy由大变为零过程TheprocessofMxydecreasingfromthemaximumtozero;
C、Mz由大变小的过程TheprocessofMzdecreasingfromthemaximumtozero;
D、Mz由小变大的过程TheprocessofMzincreasingtothemaximum