For example, when a surface coil is used to transmit a rectangular RF pulse into a uniform water phantom, the amplitude of the B1field can vary by several-fold across the imaged object.

• 比方说，当一个表面线圈向均匀的水介质发射矩形射频脉冲的时候，B1 场的振幅有可能在成像物体的不同部位发生很大的差异。