RF shimming for spectroscopic localization in the human brain at 7 T

Hoby P. Hetherington, Nikolai I. Avdievich, Andrey M. Kuznetsov, Jullie W. Pan
2009 Magnetic Resonance in Medicine  
Spectroscopic imaging of the human head at short TEs (≤15ms) typically requires suppression of signals from extracerebral tissues. However, at 7, decreasing efficiency in generation (Hz/Watt) and increasing spectral bandwidth result in dramatic increases in power deposition and increased chemical shift registration artifacts for conventional gradient based in-plane localization. In this work, we describe a novel method using RF shimming and an 8 element transceiver array to generate a field
more » ... ribution that excites a ring about the periphery of the head and leaves central brain regions largely unaffected. We have used this novel distribution to provide in-plane outer volume suppression (>98% suppression of extracerebral lipids) without the use of gradients. This novel distribution is used in conjunction with a double inversion recovery method to provide suppression of extracerebral resonances with T1s greater than 400ms, while having negligible effect on metabolite ratios of cerebral resonances with T1s >1000ms. Despite the use of two adiabatic pulses, the high efficiency of the ring distribution allows RF power deposition to be limited to 3-4W for a TR of 1.5s. The short TE enabled the acquisition of images of the human brain displaying glutamate, glutamine, macromolecules and other major cerebral metabolites.
doi:10.1002/mrm.22182 pmid:19918903 pmcid:PMC2811270 fatcat:h3pq7hh7breg7berk4vobpdg2m