What we learn from in vivo EPR oxygen images.

Distributions of oxygen concentration (pO₂) are a critical determinant of normal tissue health as well as tumor aggressiveness and response to therapy. A number of studies show the value of normal tissue and tumor tissue oxygenation images and some of these will be discussed here. A strong correlation between tumor hypoxic fraction as measured with electron paramagnetic resonance oxygen imaging and radiation treatment success or failure has been found in two separate cancer types. Oxygen images of the torso of wild type mice show initial reduction of lung, liver, visceral, and muscle pO₂ with cyclic halving of fraction of inspired oxygen (FiO₂), but variation is blunted over an hour. Spontaneous breast cancers in Mouse Mammary Tumor Viral (MMTV) promoted-polyoma middle T antigen (PyMT) mice with BNIP3, a major factor in promotion of mitochondrial autophagy, knocked out will be compared with wild type animals. Preliminary studies for the BNIP3 knock out animals show extremely low pO₂. The wide variety of studies, in which oxygen images can play an integral role, serve to demonstrate the importance of oxygen images.