Yield enhancement of a double-quantum filter sequence designed for the edited detection of GABA

To overcome limitations in the signal to noise ratio (S/N) of previously proposed multiple-quantum filters (MQFs), designed for editing the GABA A2 multiplet from the creatine (Cr) singlet in proton spectroscopy of brain, a new double-quantum filter is proposed which significantly enhances S/N (thereby making it comparable with the spin-echo difference editing technique) while maintaining the superior Cr suppression and zero vulnerability to subtraction errors of previously proposed MQFs. The S/N enhancement results primarily from a significant reduction in transverse-relaxation losses, achieved by shortening the filter sequence by approximately 70%, first by altering the criterion that determines the initial evolution period and, second, by effectively eliminating the refocusing time prior to the start of acquisition. The altered evolution time criterion also leads to an increase in the intrinsic yield of the filter from 25 to 39%. The analysis of the filter design was verified in vitro on phantoms of GABA in D2O, and the maintenance of editing capability, i.e., Cr suppression by more than 1600, was demonstrated on rat brain extracts.