Abstract: It is clearly clarified the conceptions of quadrature modulation, quadrature exciting, quadrature receiving, and quadrature demodulation in the MRI system. The purpose of quadrature modulation is to generate the SSB RF exciting pulse that avoids exciting it's mirror slice. Quadrature demodulation can distinguish positive and negative frequency so it can overcome position uncertainties on imaging data space. Quadrature exciting and quadrature receiving refer to make use of circular polarization RF coils. These quadrature operations are necessary for the optimization of MRI system and they bring some significant benefit.

Key words: MRI, quadrature modulation, quadrature exciting, quadrature receiving, quadrature demodulation

摘要： 阐明了MRI系统中所使用的正交调制、正交解调、正交激发和正交接收的概念。正交调制的目的是产生单边带RF激发脉冲，以避免激发镜像层面。正交解调能够区分正负频率，克服图像数据空间定位的不确定性。正交激发和正交接收是指运用圆极化RF线圈。指出在MRI系统中，这些正交处理是系统最佳化所要求的。阐述了这些正交处理所要求的条件以及所带来的好处，以及在系统设计和机器调试时所应遵循的原则。

关键词: MRI, 正交调制, 正交激发, 正交接收, 正交解调