Editing, faster

MEGA-PRESS editing of GABA.  It has been a reliable workhorse for the last decade, but I wonder how much longer it will rule the editing roost.  I am posting this through a haze of man flu and cough syrup, so forgive my mixed metaphors and apocalyptic tone.

MEGA-PRESS is fundamentally inefficient.  In spite of exciting all metabolite signals in a 3 cm slice of brain, through the application of two slice-selective spin echo pulses, the vast majority of signal is silenced, and then, by difference-encoding a single target metabolite, the majority of signals are consigned to the sum spectrum and ignored.  

Editing is slow, mainly because of the signal averaging required to measure low-concentration metabolites. Single-voxel single-metabolite editing is both slow and inefficient, because if you're forced to spend ten minutes doing something, you might as well do something else at the same time.

We have recently been exploring multiplexed edited experiments, and it turns out to be a rich seam to explore.  Why not join us?  Parallel imaging reconstruction allows the simultaneous acquisition of multiple excited voxels using PRIAM, and we have recently shown that MEGA-PRIAM can simultaneously edit multiple voxels.  We have also shown that MEGA-PRESS experiments can be run simultaneously to edit multiple metabolite targets, so long as the editing encoding schemes are orthogonal, using HERMES.  Thus far, HERMES has been demonstrated for simultaneous detection of NAA/NAAG and GABA/GSH, and there is a lot more to come.  It is worth noting that HERMES and PRIAM are compatible methods, and combining them allows the simultaneous editing of multiple metabolites in multiple voxels.  And finally, for now, SHERPA is an alternative approach to MEGA-PRIAM for the simultaneous edited detection of multiple voxels.  It draws on the HERMES principle of orthogonal editing encoding, but applies it spatially, using gradients to make editing pulses spatially selective.  The field of accelerated editing is just beginning and there are a lot more exciting ideas to explore.