Methods for reconstructing phase sensitive slice profiles in magnetic resonance imaging

The experimental determination of slice profiles excited by applying radiofrequency pulses in the presence of a gradient generally results in magnitude profiles. The conditions necessary to obtain a phase-sensitive picture of the profile of a slice are discussed. A distinction is made between the “excitation profile” (distribution of the transverse magnetization immediately after the RF pulse) and the “slice profile” (distribution after refocusing by gradient reversal and/or imperfect gradient switching). Methods are presented that allow one to obtain either the excitation profile or the slice profile. It is shown that phase encoding along the direction of the slice selection gradient provides a convenient protocol for obtaining the distribution of both the real and imaginary parts of the slice profile. The phase sensitive excitation profile can be obtained by frequency encoding. These methods were used to evaluate the performance of various shaped pulses.