In Vivo Measurement of Tissue Oxygen Using Electron Paramagnetic Resonance Spectroscopy with Oxygen-Sensitive Paramagnetic Particle, Lithium Phthalocy

The partial pressure of oxygen (pO₂ ) plays a determining role in the energy metabolism of aerobic cells. However, low pO₂ level induces pathophysiological conditions such as tumor hypoxia, ischemia or reperfusion injury, and delayed/altered wound healing. Especially, pO₂ level in the tumor is known to be related to tumor progression and effectiveness of radiotherapy. To monitor the pO₂ levels in vivo, continuous wave (CW) and time-domain (TD) electron paramagnetic resonance (EPR) spectroscopy method was used, in which surface coil resonator and Lithium phthalocyanine (LiPc) as oxygen sensor were crucial. Once LiPc particles are embedded in a desired location of organ/tissue, the pO₂ level can be monitored repeatedly and non-invasively. This method is based on the effect of oxygen concentration on the EPR spectra of LiPc which offers several advantages as follows: (1) high sensitivity, (2) minimum invasiveness, (3) repeated measurements, (4) absence of toxicity (non-toxic), and (5) measurement in a local region of the tissue with embedded LiPc. Therefore, in this chapter, we describe the method using CW and TD EPR spectroscopy with oxygen-sensitive particle, LiPc, for in vivo monitoring of oxygen.