India ink: A potential clinically applicable EPR oximetry probe

Using a material that already is in widespread use in humans, India ink, the first EPR measurements in a human have been made, using the India ink in a pre‐existing tattoo. The EPR spectra of India ink are very sensitive to the partial pressure of oxygen (PO₂), thereby making it feasible to use this approach to measure pO₂ in tissues in patients. This potentially provides a means to measure this parameter directly with a sensitivity, accuracy, and repeatability that have not been available previously, and thereby to be able to individualize and guide treatment of diseases such as cancer and peripheral vascular insufficiency.