title: Highly-accelerated quantitative 2D and 3D localized spectroscopy with linear algebraic modeling (SLAM) and sensitivity encoding.
abstract: Noninvasive magnetic resonance spectroscopy (MRS) with chemical shift imaging (CSI) provides valuable metabolic information for research and clinical studies, but is often limited by long scan times. Recently, spectroscopy with linear algebraic modeling (SLAM) was shown to provide compartment-averaged spectra resolved in one spatial dimension with many-fold reductions in scan-time. This was achieved using a small subset of the CSI phase-encoding steps from central image k-space that maximized the signal-to-noise ratio. Here, SLAM is extended to two- and three-dimensions (2D, 3D). In addition, SLAM is combined with sensitivity-encoded (SENSE) parallel imaging techniques, enabling the replacement of even more CSI phase-encoding steps to further accelerate scan-speed. A modified SLAM reconstruction algorithm is introduced that significantly reduces the effects of signal nonuniformity within compartments. Finally, main-field inhomogeneity corrections are provided, analogous to CSI. These methods are all tested on brain proton MRS data from a total of 24 patients with brain tumors, and in a human cardiac phosphorus 3D SLAM study at 3T. Acceleration factors of up to 120-fold versus CSI are demonstrated, including speed-up factors of 5-fold relative to already-accelerated SENSE CSI. Brain metabolites are quantified in SLAM and SENSE SLAM spectra and found to be indistinguishable from CSI measures from the same compartments. The modified reconstruction algorithm demonstrated immunity to maladjusted segmentation and errors from signal heterogeneity in brain data. In conclusion, SLAM demonstrates the potential to supplant CSI in studies requiring compartment-average spectra or large volume coverage, by dramatically reducing scan-time while providing essentially the same quantitative results.
authors.affiliation: Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, USA; Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, USA; Department of Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, TX, USA.
authors.forename: Refaat E
authors.initials: RE
authors.lastname: Gabr
authors.affiliation: Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, USA; F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA.
authors.forename: Jinyuan
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, USA; Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Weiss
authors.affiliation: Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, USA; Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, USA. Electronic address: bottoml@mri.jhu.edu.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Bottomley
mesh_terms: D000465:Algorithms; D001923:Brain Chemistry; D001932:Brain Neoplasms / Q000737:chemistry; D004574:Electromagnetic Fields; D006331:Heart Diseases / Q000378:metabolism; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008660:Metabolism; D015233:Models, Statistical; D009206:Myocardium / Q000737:chemistry; D009369:Neoplasms / Q000737:chemistry; D019047:Phantoms, Imaging; D011522:Protons
chemical_list: D011522:Protons
keywords: Brain; Cancer; Chemical shift imaging (CSI); Heart; Localized spectroscopy; SLAM