EPR oximetry is a technique that can make repeated non-invasive measurements of the pO
2 in tissues. To extend the application of EPR oximetry to humans, India ink is the probe of choice because appropriate India
inks have EPR signals whose line widths are sensitive to changes in oxygen concentrations, and, most importantly, India ink
already has been used extensively in humans as a marker in the skin, lymphatics, various organs during surgery, tumors, and
for decoration as tattoos.
We have developed an India ink that has good sensitivity to oxygen, high stability in tissues, good signal intensity, and
minimal toxicity. In this article we describe the various properties of this India ink, results obtained from our animal experiments,
and our first preliminary clinical results, which are part of the first systematic clinical use of EPR oximetry. The clinical
results indicate that it is possible to do repeated measurements over several months and probably years after the injection
of the ink, indicating that long-term follow-up studies are feasible. We are very encouraged with these results and are confident
that EPR oximetry using India ink will be a non-invasive, fast, and reliable technique for pO2 measurements in clinical studies.