50 Years of EPR Oximetry: from Capillary to Clinic

Over the last 50 years, EPR oximetry has been established as the gold standard for absolute quantitative measurement and imaging of oxygen partial pressure in the biomedical setting. In this review, the main developments in EPR oximetry through its history are discussed. The first oxygen measurement with EPR was reported approximately 50 years ago, in 1975. Since then, a wide variety of probes have been developed for various biomedical applications including preclinical and clinical study. These probes can be categorized into soluble probes including nitroxides and trityls for volumetric imaging, and solid-state probes, for long-term point measurements. Oximetry measurements range in size from a single cell to whole body rabbit imaging. The applications of preclinical EPR oximetry are still growing in scope, and include cancer, myocardial infarction, stroke, and wound healing. First studies in clinical oximetry appear promising, with discrete measurement of oxygen using injected ink or implanted OxyChip probes.