Intermolecular double-quantum coherence imaging without coherence selection gradients and its application in in vivo MRI

摘要

In the COSY Revamped with Asymmetric Z-gradient Echo Detection (CRAZED) experiments, magnetization is modulated by the distant dipolar field (DDF) generated by coherence selection gradient (CSG) commonly in sinusoidal wave-form and results in detectable intermolecular multiple-quantum coherence (iMQC) signal. IMQCs have some attractive features, but their intrinsic weak signal intensity prevents their widespread applications. In this paper, a new phase cycling scheme was applied to obtain intermolecular double-quantum coherence (iDQC) signal. It is found that DDF can arise from nonspherical sample geometry or background inhomogeneous field in the absence of CSGs, which is more efficient than that created from CSGs. The experimental results show that the resulting DDF can refocus the ± iDQC signals simultaneously and thus enhance the signal intensity to about two folds of that from the conventional CRAZED sequence. Theoretical prediction and experiments give coincident results.