Chemically induced deceleration of nuclear spin relaxation (CIDER) preserves hyperpolarization

Gadolinium-based contrast agents revolutionized magnetic resonance imaging (MRI) by accelerating spin relaxation. In contrast, agents that decelerate relaxation were hitherto unknown. Such agents are highly desirable for metabolic imaging with hyperpolarized tracers such as ¹⁵N-pyridine, 1,4-¹³C₂-succinate, and 1-¹⁵N-nicotinamide, where valuable polarization decays rapidly, especially at low fields during transfer between polarizer and scanner. Here, we report on a previously unrecognized effect in which the tracers' longitudinal and transverse relaxation rates in aqueous solution are substantially reduced by adding nicotinamide, urea, glycerol, or dendrons. The impact on longitudinal relaxation is particularly pronounced at low magnetic fields and near the tracer's pK_a where T₁ can be tripled. This mitigates polarization loss during transfer, so hitherto unsuitable, fast-relaxing molecules can be used now. This way, we achieved the ¹⁵N hyperpolarization of nearly 30% for 1-¹⁵N-nicotinamide. This chemically induced deceleration of nuclear spin relaxation (CIDER) was confirmed using magnetic field-cycling experiments and offers broad potential for hyperpolarized magnetic resonance and beyond.