Inside-out NMR with two concentric ring magnets

Shin Utsuzawa; Yiqiao Tang; Yi-Qiao Song

doi:10.1016/j.jmr.2021.107082

Inside-out NMR with two concentric ring magnets

J Magn Reson. 2021 Dec:333:107082. doi: 10.1016/j.jmr.2021.107082. Epub 2021 Oct 4.

Authors

Shin Utsuzawa¹, Yiqiao Tang², Yi-Qiao Song³

Affiliations

¹ Schlumberger-Doll Research, Cambridge, MA 02139, USA. Electronic address: sutsuzawa@slb.com.
² Schlumberger-Doll Research, Cambridge, MA 02139, USA.
³ Schlumberger-Doll Research, Cambridge, MA 02139, USA; Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA; John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.

PMID: 34688178
DOI: 10.1016/j.jmr.2021.107082

Abstract

We report the design and the implementation of an inside-out NMR sensor that produces a large sensitive region with substantially uniform magnetic field at a remote location. The construction using a pair of ring magnets is simple yet provides multiple benefits, including large sample volume, operation with low RF power, and the ability to measure samples with long T₂ and high diffusivity. A palm-size inside-out NMR sensor (57 mm OD × 29 mm height, 420 g including the housing and the coil PCB) was built with inexpensive magnets. The sweet spot is located ∼5 mm above the magnet surface with ∼4 mm width and ∼5 mm height assuming t₁₈₀ = 18 μs. The field strength at that point is 0.16 T and achieved SNR ∼23 per two scans when operated with ∼10 W peak RF power. Its quasi-uniform B₀ around the saddle point allows the measurement of T₂ = 1.5 s with a 100 μs echo time.

Keywords: Barrel magnet; Inhomogeneous fields; Inside-out NMR; Low-cost NMR; Mobile NMR; Saddle point; Single-sided NMR; Unilateral NMR.