Study for ultra-fast and highly-sensitive MR spectroscopic imaging using a high-field magnet and a high-performance gradient coil.

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A high-performance gradient system, with maximal gradient strength of 100 G/cm and inner diameter of 60 mm, was installed to a 7T high-field MR scanner. To realize highly-sensitive 1H-detected 13C spectroscopic imaging of mouse brain using hetero-nuclear multiple-quantum coherence (HMQC), a 1H RF coil system, consisting of a volume coil of 60 mm in diameter for transmission (Tx), a surface coil of 15 mm in diameter for receiving (Rx) and T/R controller, was introduced and a home-built 13C surface coil was combined. A pulse program of EPSI, which utilizes a high-speed echo planar imaging technique, was prepared, but expected increase in time-resolution was not obtained because of the small-sized mouse brain and the wide spectral band width due to the high magnetic field strength of 7T. In chemical shift imaging (CSI) with HMQC, the data acquisitions at 4 corners of k-space with8 x 8 = 64 phase encoding steps were skipped and similar spatial resolution data could be obtained in an approx. 2/3 acquisition time. Using these techniques, sequential changes in metabolite images of 13C-glutamate and glutamine generated from infused 13C-glucose were successfully observed in mouse brain with a time resolution of 20 minutes.