METHOD FOR MAINTAINING ENCODED COHERENCE FOR REMOTELY POSITIONED MRI DEVICE

摘要

A method for using a remotely positioned MRI device to image a material with an inhomogeneous magnetic field requires maintaining an encoded coherence of all components of nuclear magnetization in the material during the imaging process. To do this, the encoding of nuclei is accomplished first, and then the nuclei are repetitively refocussed'to obtain recordable net magnetic moments. This is repeated as part of a two-step recording sequence wherein first one component of the refocused nuclear magnetization is recorded and then the other component of the refocussed nuclear magnetization is recorded. Importantly, for each step in the recording sequence the encoding and the repetitive refocussing of the nuclei are accomplish separately. Specifically the method includes the steps of: tilting the nuclei with a 90.degree. pulse; encoding the nuclei with a gradient; pulsing the encoded nuclei with a train of 180.degree. pulses having a first phase angle to generate a pattern of magnetic moments; and recording the pattern. All of this is then repeated using 180.degree. pulses with a different phase angle. The method also contemplates combining a plurality of patterns to create an image of the material.