RF-SABRE: A Way to Continuous Spin Hyperpolarization at High Magnetic Fields.

Area of Science:

• Magnetic Resonance Spectroscopy
• Hyperpolarization Techniques
• Quantum Control in NMR

Background:

• Signal Amplification by Reversible Exchange (SABRE) is a hyperpolarization technique transferring spin order from parahydrogen to substrates.
• SABRE has traditionally been limited to low magnetic fields, requiring specific level anti-crossing (LAC) conditions.
• Achieving efficient spin order transfer at high fields was previously considered unfeasible without complex field-cycling setups.

Purpose of the Study:

• To demonstrate the feasibility of performing SABRE experiments at high magnetic fields.
• To introduce a novel method utilizing radiofrequency (RF) fields to achieve level anti-crossing (LAC) conditions at high fields.
• To enable the use of standard Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) hardware for hyperpolarization.

Main Methods:

• Implementation of a high-field RF-SABRE technique using commercially available NMR/MRI instruments.
• Application of a radiofrequency (RF) field to induce level anti-crossing (LAC) conditions at high magnetic fields.
• Characterization of the frequency dependence of RF-SABRE signal amplification and comparison with theoretical models.

Main Results:

• Achieved NMR signal enhancements of approximately 100-fold at 4.7 T for several substrates compared to thermal equilibrium.
• Demonstrated that RF-SABRE signal amplification is dependent on RF field frequency and amplitude, correlating with magnetic resonance parameters.
• Validated the theoretical approach through simulations showing good agreement with experimental magnetization transfer dependencies.

Conclusions:

• High-field RF-SABRE is a viable and powerful hyperpolarization technique compatible with standard NMR/MRI equipment.
• The method offers a sensitive new approach for studying transient complexes by probing spin dynamics.
• Continuous re-hyperpolarization is possible, facilitating repetitive NMR experiments and enhancing practical applications.