# Field Cycling from 10 nT to 9.4 T: A Flexible Gear Rod Design for Nuclear Spin Relaxation and Hyperpolarization Studies

## TL;DR

A new magnetic field cycling system for NMR allows rapid and flexible field changes from 9.4 T to near-zero, enabling detailed studies of nuclear spin relaxation and hyperpolarization.

## Contribution

A low-cost, compact MFC system using off-the-shelf and 3D-printed components for high-resolution NMR.

## Key findings

- The system enables sample transfer between 9.4 T and ∼nT in 1 second.
- It provides homogeneous nanotesla fields and enables T1 relaxation dispersion measurements of [1-13C]pyruvate.
- The system improves SABRE-SHEATH hyperpolarization measurements and chemical exchange rate analysis.

## Abstract

We present a flexible
gear rod-based magnetic field cycling (MFC)
system for high-resolution NMR spectrometers. The system enables the
transfer of the sample from the NMR B
0 field of 9.4 T to ∼nT and all fields in between within 1
s. A flexible gear rod was essential for reducing the total height
to approximately the height required for filling the NMR with liquid
helium. Due to its reduced height, it can be installed in average-size
NMR laboratories (the height of the NMR with MFC is only 3.32 m).
Only off-the-shelf components and 3D-printed parts were used for the
system assembly, lowering the costs for replication. An automated
shimming procedure for ultralow fields is presented to achieve homogeneous
fields of a few nanotesla. The system utility is exemplified by measuring T
1 relaxation dispersion of the most common liquid
state hyperpolarization tracer[1-13C]­pyruvateand
magnetic field dependences of signal amplification by reversible exchange,
enabling alignment transfer to heteronuclei (SABRE-SHEATH) hyperpolarization
of [15N]­pyridine. Using the system, we uncovered the exact
relaxation dispersion of pyruvate for a standard preclinical dDNP
sample composition and provided quantitative estimates for the retained
polarization after sample transfer. We modified the observation protocol
of SABRE-SHEATH polarization, which, with the high reproducibility
of the MFC, provided us with a method to measure the chemical exchange
rates of hyperpolarized compounds.