Improved selective 180° radiofrequency pulses for magnetization inversion and phase reversal

Abstract

Many efforts have been made to find a good selective 180° rf pulse, which include using amplitude and phase modulations, applying optimization techniques, and employing double-pulse techniques. While adequate selective magnetization inversion pulses have been designed, problems remain in the design of selective phase reversal pulses. In this paper we describe a novel approach which achieves large nutation angle selective rf pulses by using a series of small nutation angle pulse twins with alternated gradients (SNAPTAG). The design scheme takes into account the special properties of the rotation matrix appropriate for describing an rf pulse in the presence of a static field gradient. These pulses are suitable not only for selective magnetization inversion but also for selective phase reversal.