A broadband phased-array system for direct phosphorus and sodium metabolicMRI on a clinical scanner

Despite their proven gains in signal-to-noise ratio and field-of-view for r outine clinical MRI, phased-array detection systems are currently unavailab le for nuclei other than protons (H-1), A broadband phased-array system was designed and built to convert the H-1 transmitter signal to the non-H-1 fr equency for excitation and to convert non-H-1 phased-array MRI signals to t he H-1 frequency for presentation to the narrowband H-1 receivers of a clin ical whole-body 1.5 T MRI system. With this system, the scanner operates at the H-1 frequency, whereas phased array MRI occurs at the frequency of the other nucleus. Pulse sequences were developed for direct phased-array sodi um (Na-23) and phosphorus (P-31) MRI Of high-energy phosphates using chemic al selective imaging, thereby avoiding the complex processing and reconstru ction required for phased-array magnetic resonance spectroscopy data. Flexi ble 4-channel P-31 and Na-23 phased-arrays were built and the entire system tested in phantom and human studies. The array produced a signal-to-noise ratio improvement of 20% relative to the best-positioned single coil, but g ains of 300-400% were realized in many voxels located outside the effective field-of-view of the single coil. Cardiac phosphorus and sodium MRI were o btained in 6-13 min with 16 and 0.5 mt resolution, respectively. Lower reso lution human cardiac Na-23 MRI were obtained in as little as 4 sec, The sys tem: provides a practical approach to realizing the advantages of phased-ar rays for nuclei other than H-1, and imaging metabolites directly. (C) 2000 Wiley-Liss, Inc.