Hand-held electron spin resonance scanner for subcutaneous oximetry using OxyChip

Electron spin resonance (ESR) is used to measure oxygen partial pressure (pO₂) in biological media with many clinical applications. Traditional clinical ESR involves large magnets that encompass the subject of measurement. However, certain applications might benefit from a scanner operating within local static magnetic fields. Our group recently developed such a compact scanner for transcutaneous (surface) pO₂ measurements of skin tissue. Here we extend this capability to subsurface (subcutaneous) pO₂ measurements and verify it using an artificial tissue emulating (ATE) phantom.

We introduce a new scanner, tailored for subcutaneous measurements up to 2 mm beneath the skin's surface. This scanner captures pulsed ESR signals from embedded approximate 1-mm oxygen-sensing solid paramagnetic implant, OxyChip. The scanner features a static magnetic field source, producing a uniform region outside its surface, and a compact microwave resonator, for exciting and receiving ESR signals.

ESR readings derived from an OxyChip, positioned approximately 1.5 mm from the scanner's surface, embedded in ATE phantom, exhibited a linear relation of 1/T₂ versus pO₂ for pO₂ levels at 0, 7.6, 30, and 160 mmHg, with relative reading accuracy of about 10%.

The compact ESR scanner can report pO₂ data in ATE phantom from an external position relative to the scanner. Implementing this scanner in preclinical and clinical applications for subcutaneous pO₂ measurements is a feasible next phase for this development. This innovative design also has the potential to operate in conjunction with artificial skin graft for wound healing, combining therapeutic and pO₂ diagnostic features.