Simultaneous metabolic and functional imaging of the brain using SPICE

Abstract

Purpose: To enable simultaneous high-resolution mapping of brain function and metabolism.

Methods: An encoding scheme was designed for interleaved acquisition of functional MRI (fMRI) data in echo volume imaging trajectories and MR spectroscopic imaging (MRSI) data in echo-planar spectroscopic imaging trajectories. The scheme eliminates water and lipid suppression and utilizes free induction decay signals to encode both functional and metabolic information with ultrashort TE, short TR, and sparse sampling of $\left(k,t\right)$ -space. A subspace-based image reconstruction method was introduced for processing both the fMRI and MRSI data. The complementary information in the fMRI and MRSI data sets was also utilized to improve image reconstruction in the presence of intrascan head motion, field drift, and tissue susceptibility changes.

Results: In-vivo experimental results were obtained from healthy human subjects in resting-state fMRI/MRSI experiments. In these experiments, the proposed method was able to simultaneously acquire metabolic and functional information from the brain in high resolution. For scans of 6.5 minutes, we achieved 3.0 × 3.0 × 1.8 mm³ spatial resolution for fMRI, 1.9 × 2.5 × 3.0 mm³ nominal spatial resolution for MRSI, and 1.9 × 1.9 × 1.8 mm³ nominal spatial resolution for quantitative susceptibility maps.

Conclusion: This work demonstrates the feasibility of simultaneous high-resolution mapping of brain function and metabolism with improved spatial resolution and synergistic image reconstruction.

Keywords: QSM; SPICE; fMRI; partial separability; sparse sampling; ultra-high-resolution MRSI.