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An NMR imaging method, called spin invesion (SI) imaging, is described for imaging under a magnetic field with high nonuniformity. 180 degrees flips are applied between sampling times of the FID to remove the effects of field nonuniformities on the FID. The only requirement for SI imaging is to have high enough RF power. This requirement may be satisfied safely for small volume imaging, for example, head scanning. The advantages of SI imaging are that the images produced are almost independent of the effects of main-field nonuniformities and chemical shifts, and that there is no stringent requirement on the gradient pulse shapes. In this paper, the technique is described, gradient and sampling period requirements are derived, methods for reducing the RF peak power needed are developed, and a computer simulation to demonstrate the technique is presented.
Wong et al. (Mon,) studied this question.