Time-Resolved EPR Imaging

time_resolved_imaging.jpg Time dependence of pO2 from different regions of mouse leg during FiO2 modulation experiment. Area 1 is located on the tumor periphery, while area 2 is inside the tumor. The effect of PCA on T1/R1 images and correlation image of FiO2 function and animal pO2 are shown. Time resolution 2.5 min.

Using the partially deuterated trityl OX063d24 we were able to reduce the acquisition time to up to 1 minute per image. In order to assess the sensitivity of the tissues pO2 to transient changes in hypoxia, we subjected mice to alternation in the fraction of inhaled O2 (FiO2) of the inhaled gas.  The driving FiO2 in the Figure is shown above on the right along with the sequence of pO2values from the 27 voxels from the hypoxic tumor region [2] and the better oxygenated region [1] in the tumor periphery indicated by red contour. 

This technology is the basis for the development of major tools for the analysis of the relationship between temporal pO2 variation of normal tissue and tumor tissue and the absolute levels of oxygenation.  These, in turn, must be analyzed relative to the response to therapy.  The temporal correlation needs to be investigated as to which of these patterns is the most significant determinant of tumor resistance to radiation and chemotherapy.