Simultaneous QSM and metabolic imaging of the brain using SPICE

• Published in: Magnetic resonance in medicine Vol. 79; no. 1; pp. 13 - 21
• Main Authors: Peng, Xi, Lam, Fan, Li, Yudu, Clifford, Bryan, Liang, Zhi‐Pei
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.01.2018
• Subjects: Algorithms; Brain; Brain - diagnostic imaging; Brain mapping; Brain Mapping - methods; Data acquisition; Data processing; Echoes; Healthy Volunteers; Humans; Image Interpretation, Computer-Assisted - methods; Image Processing, Computer-Assisted; Imaging; In vivo methods and tests; Magnetic permeability; Magnetic resonance; Magnetic Resonance Imaging - methods; Magnetic susceptibility; Mapping; Metabolism; Metabolites; Models, Statistical; Neuroimaging; partial separability; quantitative susceptibility mapping; Reproducibility of Results; Sampling; Signal-To-Noise Ratio; Spatial resolution; spectroscopic imaging; SPICE; Subspace methods; subspace modeling; Subspaces; Water - metabolism; SPICE; quantitative susceptibility mapping; spectroscopic imaging; subspace modeling; partial separability
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.26972

Purpose To map brain metabolites and tissue magnetic susceptibility simultaneously using a single three‐dimensional 1H‐MRSI acquisition without water suppression. Methods The proposed technique builds on a subspace imaging method called spectroscopic imaging by exploiting spatiospectral correlation (SPICE), which enables ultrashort echo time (TE)/short pulse repetition time (TR) acquisitions for 1H‐MRSI without water suppression. This data acquisition scheme simultaneously captures both the spectral information of brain metabolites and the phase information of the water signals that is directly related to tissue magnetic susceptibility variations. In extending this scheme for simultaneous QSM and metabolic imaging, we increase k‐space coverage by using dual density sparse sampling and ramp sampling to achieve spatial resolution often required by QSM, while maintaining a reasonable signal‐to‐noise ratio (SNR) for the spatiospectral data used for metabolite mapping. In data processing, we obtain high‐quality QSM from the unsuppressed water signals by taking advantage of the larger number of echoes acquired and any available anatomical priors; metabolite spatiospectral distributions are reconstructed using a union‐of‐subspaces model. Results In vivo experimental results demonstrate that the proposed method can produce susceptibility maps at a resolution higher than 1.8 × 1.8 × 2.4 mm3 along with metabolite spatiospectral distributions at a nominal spatial resolution of 2.4 × 2.4 × 2.4 mm3 from a single 7‐min MRSI scan. The estimated susceptibility values are consistent with those obtained using the conventional QSM method with 3D multi‐echo gradient echo acquisitions. Conclusion This article reports a new capability for simultaneous susceptibility mapping and metabolic imaging of the brain from a single 1H‐MRSI scan, which has potential for a wide range of applications. Magn Reson Med 79:13–21, 2018. © 2017 International Society for Magnetic Resonance in Medicine.