Dynamic nuclear polarization (DNP) for the enhancement of the NMR signals of specific metabolites has recently found applications in the context of magnetic resonance imaging (MRI). Currently, DNP signal enhancement is implemented in clinical systems through the use of exogenous stable organic free radicals, known as polarization agents (PAs), mixed in a solution with the metabolite of interest. These PAs are medically undesirable and thus must be filtered out prior to patient injection - a task that involves considerable technical complexity and consumes valuable time during which the polarization decays. Here, we aim to demonstrate DNP enhancements large enough for clinical relevance using a process free of exogenous PAs. This is achieved by processing (soft grinding) the metabolite in its solid form and subsequently exposing it to plasma in a dilute atmosphere to produce chemically-unstable free radicals (herein referred to as electrical-discharge-induced radicals - EDIRs) within the powder. These samples are then subjected to the normal DNP procedure of microwave irradiation while placed under a high static magnetic field, and their NMR signal is measured to quantify the enhancement of the protons’ signal in the solid. Proton signal enhancements (measured as the ratio of the NMR signal with microwave irradiation to the NMR signal without microwave irradiation) of up to 150 are demonstrated in glucose. Upon fast dissolution, the free radicals are annihilated, leaving the sample in its original chemical composition (which is safe for clinical use) without any need for filtration and cumbersome quality control procedures. We thus conclude that EDIRs are found to be highly efficient in providing DNP enhancement levels that are on par with those achieved with the exogenous PAs, while being safe for clinical use. This opens up the possibility of applying our method to clinical scenarios with minimal risks and lower costs per procedure.

动态核极化（DNP）用于增强特定代谢产物的NMR信号，最近在磁共振成像（MRI）中得到了应用。当前，在临床系统中通过使用外源性稳定的有机自由基（称为极化剂（PAs））与感兴趣的代谢产物混合来实现DNP信号增强。这些功率放大器在医学上是不希望有的，因此必须在患者注射之前将其滤除-这是一项涉及相当大的技术复杂性的工作，并消耗了极化衰减的宝贵时间。在这里，我们旨在证明使用不含外源性PA的过程，DNP增强的幅度足以达到临床相关性。这是通过加工（软磨）固体形式的代谢物，然后将其在稀薄的空气中暴露于血浆中以在粉末内产生化学不稳定的自由基（在本文中称为放电诱导的自由基-EDIR）来实现的。然后将这些样品置于高静态磁场下，然后进行常规的微波辐照DNP程序，并测量其NMR信号以量化固体中质子信号的增强。在葡萄糖中，质子信号增强高达150（以微波辐照的NMR信号与没有微波辐照的NMR信号的比值测量）。快速溶解后，自由基被ni灭，使样品保持其原始化学成分（可安全用于临床），而无需进行过滤和繁琐的质量控制程序。因此，我们得出的结论是，发现EDIR在提供DNP增强水平方面非常有效，而DNP增强水平与外源性PA达到的水平相当，同时对临床使用是安全的。这开辟了将我们的方法应用于临床案例的可能性，从而将风险降至最低并降低了每次操作的成本。