On the application of ultra‐fast rare experiments

Abstract

The ultra‐fast application of the RARE experiment is described in detail, with special emphasis on its multifarious applications with preparation experiments that produce transverse magnetization. The factors affecting the temporal evolution of the magnetization during the experiment are described, and the implications for the slice profile when using a Gaussian refocusing pulse are experimentally examined. The choice of phase‐encoding scheme for use with preparation experiments is discussed, as is the use of various phase‐encoding schemes to reduce line broadening in the phase‐encoding direction if a number of averages are acquired. An explanation for the decomposition of the echo are into two components if the read gradient is imbalanced is given, and the experimental conditions necessary for the coherent addition of these two echo groups are described. An alternative sequence that removes one of these groups from the acquisition window is proposed. The sensitivity of the sequence to flow and motion is investigated, and the drastic loss of signal in this situation explained. The in vivo and in vitro application of preparation experiments leading to the accurate measurement of T 1, T 2, diffusion constant, and magnetization transfer characteristics is presented. The implementation of zoom‐imaging using spin‐ and stimulated‐echo preparation is described, and 3D in vivo spin‐echo zoom images are presented. Simple phantom experiments demonstrating the feasibility of chemical‐shift selective and spectroscopic imaging are also given.