Abstract: Imperfection of analog components and influence of distributed parameters led to the rf leakage in the modulation of a shaped pulse.The rf leakage produced big artifact to the excitation profile of the shaped pulse.In this article,the artifact was analyzed on the basis of the theory of rf amplitude modulation.A new phase cycling pulse sequence was designed to reduce such kind of artifact.Experimental result showed that this phase cycling method is practical to the improvement of the feature in the selective excitation unit.

Key words: Shaped pulse modulation, Analog multiplier, RF leakage, Phase cycling