TY - JOUR
T1 - Covariance J-resolved spectroscopy
T2 - Theory and application in vivo
AU - Iqbal, Zohaib
AU - Verma, Gaurav
AU - Kumar, Anand
AU - Thomas, M. Albert
N1 - Funding Information:
The authors acknowledge the National Institute of Health R21 Grant (NS080648-02) and the University of California–Los Angeles Dissertation Year Fellowship Award (2016–2017).
Publisher Copyright:
Copyright © 2017 John Wiley & Sons, Ltd.
PY - 2017/8
Y1 - 2017/8
N2 - Magnetic resonance spectroscopy (MRS) is a powerful tool capable of investigating the metabolic status of several tissues in vivo. In particular, single-voxel-based 1H spectroscopy provides invaluable biochemical information from a volume of interest (VOI) and has therefore been used in a variety of studies. Unfortunately, typical one-dimensional MRS data suffer from severe signal overlap and thus important metabolites are difficult to distinguish. One method that is used to disentangle overlapping resonances is the two-dimensional J-resolved spectroscopy (JPRESS) experiment. Due to the long acquisition duration of the JPRESS experiment, a limited number of points are acquired in the indirect dimension, leading to poor spectral resolution along this dimension. Poor spectral resolution is problematic because proper peak assignment may be hindered, which is why the zero-filling method is often used to improve resolution as a post-processing step. However, zero-filling leads to spectral artifacts, which may affect visualization and quantitation of spectra. A novel method utilizing a covariance transformation, called covariance J-resolved spectroscopy (CovJ), was developed in order to improve spectral resolution along the indirect dimension (F1). Comparison of simulated data demonstrates that peak structures remain qualitatively similar between JPRESS and the novel method along the diagonal region (F1 = 0 Hz), whereas differences arise in the cross-peak (F1≠0 Hz) regions. In addition, quantitative results of in vivo JPRESS data acquired on a 3T scanner show significant correlations (r2>0.86, p<0.001) when comparing the metabolite concentrations between the two methods. Finally, a quantitation algorithm, ‘COVariance Spectral Evaluation of 1H Acquisitions using Representative prior knowledge’ (Cov-SEHAR), was developed in order to quantify γ-aminobutyric acid and glutamate from the CovJ spectra. These preliminary findings indicate that the CovJ method may be used to improve spectral resolution without hindering metabolite quantitation for J-resolved spectra.
AB - Magnetic resonance spectroscopy (MRS) is a powerful tool capable of investigating the metabolic status of several tissues in vivo. In particular, single-voxel-based 1H spectroscopy provides invaluable biochemical information from a volume of interest (VOI) and has therefore been used in a variety of studies. Unfortunately, typical one-dimensional MRS data suffer from severe signal overlap and thus important metabolites are difficult to distinguish. One method that is used to disentangle overlapping resonances is the two-dimensional J-resolved spectroscopy (JPRESS) experiment. Due to the long acquisition duration of the JPRESS experiment, a limited number of points are acquired in the indirect dimension, leading to poor spectral resolution along this dimension. Poor spectral resolution is problematic because proper peak assignment may be hindered, which is why the zero-filling method is often used to improve resolution as a post-processing step. However, zero-filling leads to spectral artifacts, which may affect visualization and quantitation of spectra. A novel method utilizing a covariance transformation, called covariance J-resolved spectroscopy (CovJ), was developed in order to improve spectral resolution along the indirect dimension (F1). Comparison of simulated data demonstrates that peak structures remain qualitatively similar between JPRESS and the novel method along the diagonal region (F1 = 0 Hz), whereas differences arise in the cross-peak (F1≠0 Hz) regions. In addition, quantitative results of in vivo JPRESS data acquired on a 3T scanner show significant correlations (r2>0.86, p<0.001) when comparing the metabolite concentrations between the two methods. Finally, a quantitation algorithm, ‘COVariance Spectral Evaluation of 1H Acquisitions using Representative prior knowledge’ (Cov-SEHAR), was developed in order to quantify γ-aminobutyric acid and glutamate from the CovJ spectra. These preliminary findings indicate that the CovJ method may be used to improve spectral resolution without hindering metabolite quantitation for J-resolved spectra.
KW - covariance NMR
KW - enhanced spectral resolution
KW - human brain
KW - J-resolved spectroscopy (JPRESS)
KW - Magnetic Resonance Spectroscopy (MRS)
KW - prior-knowledge fitting
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U2 - 10.1002/nbm.3732
DO - 10.1002/nbm.3732
M3 - Article
C2 - 28481039
AN - SCOPUS:85019135015
SN - 0952-3480
VL - 30
JO - NMR in biomedicine
JF - NMR in biomedicine
IS - 8
M1 - e3732
ER -