In Vivo Measurement of Tissue Oxygen Using Electron Paramagnetic Resonance Spectroscopy with Oxygen-

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.