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.