[Imaging of Tumor-Specific Hypoxia Dynamics and Its Significance in Radiation Biology].

Hypoxia has been known to be a feature associated with tumor radioresistance. So far, clinical strategies to overcome chronic hypoxia due to the limitation of the oxygen diffusion have been designed. However, intermittent or acute/cycling hypoxia, whose frequency can range between a few cycles per minutes to hours, is receiving increased attention, because this type of hypoxia has been reported to have an influence on tumor malignancy as well as treatment resistance via increased expression of pro-survival pathways. Therefore, a priori information on fluctuating hypoxia can be important in clinical treatment planning, but complicated dynamics makes it difficult to elucidate biological significance of intermittent hypoxia.Here, we illustrate the use of pulsed electron spin resonance imaging (ESRI) as a novel imaging method to directly monitor fluctuating oxygenation i.e. cycling hypoxia in transplanted tumors. A common resonator platform for both ESRI and magnetic resonance imaging (MRI) provided pO