Biological validation of electron paramagnetic resonance (EPR) image oxygen thresholds in tissue

Measuring molecular oxygen levels in vivo has been the cornerstone of understanding the effects of hypoxia in normal tissues and malignant tumors. Here we discuss the advances in a variety of partial pressure of oxygen (PO2) measurements and imaging techniques and relevant oxygen thresholds. A focus on electron paramagnetic resonance (EPR) imaging shows the validation of treating hypoxic tumours with a threshold of PO2 ≤ 10 Torr, and demonstrates utility for in vivo oxygen imaging, as well as its current and future role in cancer studies. figure legend Electron paramagnetic resonance (EPR) is a powerful tool for quantitative imaging of PO2 to study and treat tumour hypoxia. This example shows a preclinical tumour mouse model injected with an oxygen spin probe (OX063‐d24) into the tail vein for diffusion throughout the tumour, and the resulting hypoxic regions defined by PO2 ≤ 10 Torr obtained by EPR imaging.