title: A broadband phased-array system for direct phosphorus and sodium metabolic MRI on a clinical scanner.
abstract: Despite their proven gains in signal-to-noise ratio and field-of-view for routine clinical MRI, phased-array detection systems are currently unavailable for nuclei other than protons (1H). A broadband phased-array system was designed and built to convert the 1H transmitter signal to the non-1H frequency for excitation and to convert non-1H phased-array MRI signals to the 1H frequency for presentation to the narrowband 1H receivers of a clinical whole-body 1.5 T MRI system. With this system, the scanner operates at the 1H frequency, whereas phased-array MRI occurs at the frequency of the other nucleus. Pulse sequences were developed for direct phased-array sodium (23Na) and phosphorus (31P) MRI of high-energy phosphates using chemical selective imaging, thereby avoiding the complex processing and reconstruction required for phased-array magnetic resonance spectroscopy data. Flexible 4-channel 31P and 23Na 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 gains 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 obtained in 6-13 min with 16 and 0.5 mL resolution, respectively. Lower resolution human cardiac 23Na MRI were obtained in as little as 4 sec. The system provides a practical approach to realizing the advantages of phased-arrays for nuclei other than 1H, and imaging metabolites directly.
authors.affiliation: Department of Radiology, Johns Hopkins University, Baltimore, Maryland 21287-0843, USA.
authors.forename: R F
authors.initials: RF
authors.lastname: Lee
authors.forename: R
authors.initials: R
authors.lastname: Giaquinto
authors.forename: C
authors.initials: C
authors.lastname: Constantinides
authors.forename: S
authors.initials: S
authors.lastname: Souza
authors.forename: R G
authors.initials: RG
authors.lastname: Weiss
authors.forename: P A
authors.initials: PA
authors.lastname: Bottomley
mesh_terms: D000669:Amplifiers, Electronic; D016477:Artifacts; D004867:Equipment Design; D005260:Female; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods / Q000706:statistics & numerical data; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods / Q000706:statistics & numerical data; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D012964:Sodium / Q000378:metabolism*; D012975:Sodium Isotopes; D012984:Software
chemical_list: D010761:Phosphorus Radioisotopes; D012975:Sodium Isotopes; D010758:Phosphorus; D012964:Sodium