title: Development and performance of a 129-GHz dynamic nuclear polarizer in an ultra-wide bore superconducting magnet.
abstract: OBJECTIVE
  We sought to build a dynamic nuclear polarization system for operation at 4.6 T (129 GHz) and evaluate its efficiency in terms of (13)C polarization levels using free radicals that span a range of ESR linewidths.
  
  
  METHODS
  A liquid helium cryostat was placed in a 4.6 T superconducting magnet with a 150-mm warm bore diameter. A 129-GHz microwave source was used to irradiate (13)C enriched samples. Temperatures close to 1 K were achieved using a vacuum pump with a 453-m(3)/h roots blower. A hyperpolarized (13)C nuclear magnetic resonance (NMR) signal was detected using a saddle coil and a Varian VNMRS console operating at 49.208 MHz. Samples doped with free radicals BDPA (1,3-bisdiphenylene-2-phenylallyl), trityl OX063 (tris{8-carboxyl-2,2,6,6-benzo(1,2-d:4,5-d)-bis(1,3)dithiole-4-yl}methyl sodium salt), galvinoxyl ((2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy), 2,2-diphenylpicrylhydrazyl (DPPH) and 4-oxo-TEMPO (4-Oxo-2,2,6,6-tetramethyl-1-piperidinyloxy) were assayed. Microwave dynamic nuclear polarization (DNP) spectra and solid-state (13)C polarization levels for these samples were determined.
  
  
  RESULTS
  (13)C polarization levels close to 50 % were achieved for [1-(13)C]pyruvic acid at 1.15 K using the narrow electron spin resonance (ESR) linewidth free radicals trityl OX063 and BDPA, while 10-20 % (13)C polarizations were achieved using galvinoxyl, DPPH and 4-oxo-TEMPO.
  
  
  CONCLUSIONS
  At this field strength free radicals with smaller ESR linewidths are still superior for DNP of (13)C as opposed to those with linewidths that exceed that of the (1)H Larmor frequency.
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390, USA.
authors.forename: Lloyd L
authors.initials: LL
authors.lastname: Lumata
authors.forename: Richard
authors.initials: R
authors.lastname: Martin
authors.forename: Ashish K
authors.initials: AK
authors.lastname: Jindal
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Kovacs
authors.forename: Mark S
authors.initials: MS
authors.lastname: Conradi
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Merritt
mesh_terms: D066241:Carbon-13 Magnetic Resonance Spectroscopy / Q000295:instrumentation*; D017076:Computer-Aided Design; D004553:Electric Conductivity; D004867:Equipment Design; D019544:Equipment Failure Analysis; D059346:Magnets; D008872:Microwaves; D012031:Refractometry / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity