title: 3D spatially encoded and accelerated TE-averaged echo planar spectroscopic imaging in healthy human brain.
abstract: Several different pathologies, including many neurodegenerative disorders, affect the energy metabolism of the brain. Glutamate, a neurotransmitter in the brain, can be used as a biomarker to monitor these metabolic processes. One method that is capable of quantifying glutamate concentration reliably in several regions of the brain is TE-averaged (1) H spectroscopic imaging. However, this type of method requires the acquisition of multiple TE lines, resulting in long scan durations. The goal of this experiment was to use non-uniform sampling, compressed sensing reconstruction and an echo planar readout gradient to reduce the scan time by a factor of eight to acquire TE-averaged spectra in three spatial dimensions. Simulation of glutamate and glutamine showed that the 2.2-2.4 ppm spectral region contained 95% glutamate signal using the TE-averaged method. Peak integration of this spectral range and home-developed, prior-knowledge-based fitting were used for quantitation. Gray matter brain phantom measurements were acquired on a Siemens 3 T Trio scanner. Non-uniform sampling was applied retrospectively to these phantom measurements and quantitative results of glutamate with respect to creatine 3.0 (Glu/Cr) ratios showed a coefficient of variance of 16% for peak integration and 9% for peak fitting using eight-fold acceleration. In vivo scans of the human brain were acquired as well and five different brain regions were quantified using the prior-knowledge-based algorithm. Glu/Cr ratios from these regions agreed with previously reported results in the literature. The method described here, called accelerated TE-averaged echo planar spectroscopic imaging (TEA-EPSI), is a significant methodological advancement and may be a useful tool for categorizing glutamate changes in pathologies where affected brain regions are not known a priori. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Department of Radiological Sciences, University of California Los Angeles, USA.
authors.forename: Zohaib
authors.initials: Z
authors.lastname: Iqbal
authors.affiliation: Department of Radiological Sciences, University of California Los Angeles, USA.
authors.forename: Neil E
authors.initials: NE
authors.lastname: Wilson
authors.affiliation: Department of Radiological Sciences, University of California Los Angeles, USA.
authors.forename: M Albert
authors.initials: MA
authors.lastname: Thomas
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging*; D003198:Computer Simulation; D003401:Creatine / Q000378:metabolism; D017352:Echo-Planar Imaging / Q000379:methods*; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D021621:Imaging, Three-Dimensional; D055442:Metabolome; D009010:Monte Carlo Method; D055815:Young Adult
chemical_list: D005973:Glutamine; D018698:Glutamic Acid; D003401:Creatine
keywords: 3D spectroscopic imaging; TE-averaged; compressed sensing; glutamate quantitation; human brain; non-uniform sampling