A Decade of Experience With the UltraWide-Bore 900-MHz NMR Magnet

Abstract

The ultrawide-bore (UWB) 900 MHz NMR magnet was commissioned in 2004. The magnet was conceived as part of the long range goal of NMR at fields in excess of 25 T that would require inner high temperature superconductor coils in the bore of a low temperature superconductor outer magnet of a sufficiently large bore. In order to address the combined interest in reaching 900 MHz while at the same time advancing the technology of large LTS NMR magnets, the decision was made to produce a 900 MHz magnet with an extended large bore to force the development of technology and for demonstration. Several advances in magnet technology were made in addition to the large bore in the areas of epoxy for impregnation and quench protection. During fabrication of the magnet, a joint between coil sections was possibly damaged, resulting in a large field drift in persistent mode. The cancelation of the field drift was initially a challenge but resulted in an excellent opportunity for the further development of drift compensation methods. Once the extended large bore was available, it was found to be increasingly of interest for unique NMR measurements. Since commissioning, the UWB magnet has played a central role in the NMR science program at the NHMFL. Major programs conducted in the magnet include biological solid state NMR both of uniformly oriented samples of membrane proteins that often represent drug targets for the pharmaceutical industry and magic angle sample spinning. The extended wide bore has allowed the magnet to be used for imaging at the high field of 21 T, including studies of high resolution 1 H images of adult rodents, 23 Na imaging in models ranging from single cells to in vivo rats to establish dynamic distributions of ionic sodium in pathological (stroke) and non-pathological (activation) conditions, and multi-modal nanoparticles used to track implanted cells as part of a cellular therapy for neurodegeneration. In addition 23 Na and 35 Cl images of in vivo tumors in animal models have suggested important potential roles for evaluating pharmaceutical efficacy and other medical applications.

Brain investigations of rodent disease models by chemical exchange saturation transfer at 21.1 T

“…All data were acquired using the 105‐mm bore, 21.1‐T (900‐MHz) vertical magnet available at the National High Magnetic Field Laboratory MRI/MRS user facility in Tallahassee, Florida . The magnet is equipped with a Bruker Avance III console running Paravision ® 5.1 (Bruker Biospin, Billerica, MA) and imaging gradients (Resonance Research Inc., Billerica, MA) delivering a peak strength of 600 mT/m with rise times of 120 μs.…”

“…All data were acquired using the 105-mm bore, 21.1-T (900-MHz) vertical magnet available at the National High Magnetic Field Laboratory MRI/MRS user facility in Tallahassee, Florida. 39 The magnet is equipped with a Bruker Avance III console running Paravision ® 5.1 (Bruker Biospin, Billerica, MA) and imaging gradients (Resonance Research Inc., Billerica, MA) delivering a peak strength of 600 mT/m with rise times of 120 μs. A custom-built transmit/receive quadrature double-saddle surface coil was used in these 1 H magnetic resonance experiments, whose performance, including B 1 specifications, has been described recently.…”

Distinguishing neuronal from astrocytic subcellular microstructures using in vivo Double Diffusion Encoded 1H MRS at 21.1 T

“…All animal procedures were undertaken according to these regulatory bodies and AAALAC guidelines. The experiments took place at the US National High Magnetic Field Laboratory’s 21.1 T MRI/NMR (900 MHz 1 H frequency [ 61 , 62 ], equipped with a Bruker Avance III console, a RRI Inc. gradient system capable of producing up to 60 G/cm in all dimensions, and a customized quadrature surface coil probe [ 63 ]. Naïve Sprague Dawley rats were purchased from Envigo Corp. (Tampa, FL, USA) and delivered one week prior to surgery for acclimatization to the new environment.…”

Multiparametric classification of sub‐acute ischemic stroke recovery with ultrafast diffusion, 23Na, and MPIO‐labeled stem cell MRI at 21.1 T

“…An approximate B 0 magnetic field strength scaling of SNR ∝B 0 1.65 is observed for protons that tapers off to a more linear increase between 9.4 and 21.1 T. For X nuclei such as 23 Na conducting these scans at the highest small animal imaging system to date, 21.1 T provides up to a 3-fold gain in sensitivity compared with preclinical tests previously conducted at 9.4 T (12,13). Higher SNR provides higher-contrast images for stroke detection with reduced scan times (13)(14)(15), improved quantification of ADC utilizing high b-values (16). Enhancement of local susceptibility contrast needed for detection of paramagnetic-labeled cells in the brains of ischemic animals is also maximized for iron nanoparticles (17)(18)(19).…”

“…This study included MPIO-labeled hMSC tracking, ADC measurements, and 23 Na imaging, measurements of ongoing interest due to efforts in advancing high-field stroke research, as well as in the context of theranostic interventions (13,(15)(16)(17)(18)(19)24,(45)(46)(47). Our focus on these imaging approaches and characterization of sub-acute timelines differ somewhat from previous combinations of perfusion and diffusion imaging during acute stroke onset (4,22,29,35,37,39,44).…”