OxyTrack : A Novel Needle Sensor for In Situ Oximetry

ABSTRACT Purpose In vivo electron paramagnetic resonance (EPR) oximetry is a powerful method for tissue oxygen measurements. OxyChip is an implantable probe that is widely used in animal models and currently being evaluated for use in human subjects. The OxyChip requires an external resonator (RF coil) capable of sufficient depth sensitivity, preferably up to 4 cm or more, which is a limitation for existing resonators. The goal of present study was to develop a novel sensor/device, called OxyTrack, for deep‐tissue oximetry. Methods Several OxyTracks consisting of coax‐tip micro‐loop resonator embedded with OxyChip were designed using various needles (0.5–1 mm outer diameter; 3–17 cm length) and tested using an L‐band continuous wave EPR spectrometer. Results The OxyTrack showed high signal‐to‐noise ratio (SNR) at low RF powers, for example SNR of 86 at 45‐nW incident power. The orientation of the sensor with respect to the magnetic field ( B 0 ) or the depth of insertion into tissue had no significant effect on the measured oxygen values. OxyTrack demonstrated quick response to dynamic changes in oxygen levels and stability to sterilization by autoclaving and ionizing radiation. In vivo measurements in tumor‐bearing mouse demonstrated differences in tissue oxygenation in healthy muscle compared to malignant tissues. Compatibility of the OxyTrack with common medical imaging methods was established to register the anatomic location of the sensor in the tissue. Conclusion The OxyTrack technology represents a significant advancement in the practice of EPR oximetry for in situ monitoring of deep‐tissue oxygenation.