3D spatially encoded and accelerated TE‐averaged echo planar spectroscopic imaging in healthy human brain. (8th January 2016)

• Record Type: Journal Article
• Authors: Iqbal, Zohaib; Wilson, Neil E.; Thomas, M. Albert
• Is Part Of: NMR in biomedicine. Volume 29:Number 3(2016:Mar.)
• Page Start: 329
• Page End: 339
• Publication Date: 2016-01-08
• Subjects: TE‐averaged -- compressed sensing -- non‐uniform sampling -- human brain -- 3D spectroscopic imaging -- glutamate quantitation; Nuclear magnetic resonance -- Periodicals; Magnetic Resonance Spectroscopy -- Periodicals; 574
• DOI: 10.1002/nbm.3469
• Languages: English
• ISSNs: 0952-3480

Abstract

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. Abstract : A novel method combining non‐uniform sampling and compressed sensing reconstruction was developed to acquire TE‐averaged spectra from three spatial dimensions with an eightfold acceleration in scan time. This method was applied in phantom as well as in the human brain and a MATLAB based, prior‐knowledge fitting algorithm was implemented to quantify metabolites. Glutamate concentrations were in agreement with previous findings for different regions of the brain, where gray matter regions had higher glutamate concentrations than white matter regions.