A novel analysis of selective excitation and phase reversal

The Bloch equations are reanalyzed in a spherical coordinate system for shaped RF pulses applied in the presence of a static magnetic field gradient. In such a system the behavior of large angle-selective RF pulses can be better compared to small angle nutations and in particular the performance of 180° pulsed use for spin inversion and phase reversal can be better described. It is found that the major problem using conventional 180° sinc-shaped pulses is the phase change that arises when the magnetization passes through the transverse plane. Alterations in the magnetic field gradient compensate for such a phase change and thereby improve the performance of selective pulses for both spin inversion and phase reversal. © 1987.