A Flexible RF Coil Design (OxyTrack) for Oxygen Measurements in Body Cavities

Electron paramagnetic resonance (EPR) spectroscopy enables quantitative measurement of tissue oxygen levels. The conventional single-loop EPR resonator designs limit the oxygen measurements to superficial tissues within 1-3 cm depth and inadequately address clinical requirements for deep-tissue oxygen monitoring in anatomically complex regions and confined body cavities. The aim of this study was to develop a flexible RF coil-based sensor (OxyTrack) designed for real-time oxygen measurements in complex anatomical environments that are typically inaccessible to conventional rigid coil configurations.

The RF coil configuration of the OxyTrack included a catheter-like, flexible design that incorporates the OxyChip (oxygen sensor) in the resonant loop. A modified coaxial cable arrangement with braided shielding was used for cavity measurements. The constructed coil/sensor was evaluated for power saturation thresholding, oxygen sensitivity (calibration), mechanical stability, and integrity of the coil under various stress conditions. Biological validation studies were performed to test dynamic oxygen variations in the gastrointestinal tract (GI) of murine subjects.

The flexible OxyTrack exhibited an oxygen sensitivity of 14.8 mG/mmHg with a linear response across physiological ranges (0-160 mmHg), maintaining signal integrity under various mechanical stresses. In vivo validation experiments in mice GI tracts demonstrated statistically significant discrimination of rectal tissue oxygenation between normoxic (0.52 ± 0.04 mmHg) and hyperoxic conditions (6.43 ± 0.24 mmHg) with p < 0.001. Pre-clinical imaging compatibility established the absence of significant artifacts.

This flexible RF coil sensor enables minimally invasive, real-time oxygen monitoring in complex anatomical locations, with implications for pre-clinical research and potential clinical translation in oxygen-related pathophysiology assessment.