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

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 <i>B</i> 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 <i>T</i> 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.