The importance of tissue and tumor oxygenation in malignancy and other pathophysiologic conditions has spawned a number of oxymetries. Comparison of different modalities is crucial for the validation and understanding of these techniques. Electron Paramagnetic Resonance (EPR) Imaging is a novel technique for providing quantitative high resolution images of tumor and tissue oxygenation. Our Center has optimized imaging with a rapid, CW technique, using novel, narrow line trityl spin probes (OX063, Nycomed/Amersham Health R&D) injected IV into mice, spectroscopic imaging and image analysis techniques,. These have produced high resolution line width images. Simple calibration curves directly relate the line width to the local voxel oxygen concentration giving quantitative oxygen images. This paper describes a comparison between EPR oxygen images and sequences of oxygen measurement made with an Oxylite™ oxygen probe by reconstructing the Oxylite™ track position in the EPR oxygen image. Such 4D EPR image, obtained in 45 minutes from 10 mm FSa fibrosarcomas grown in the legs of C3H mice. The reconstructed image of the tumor has the spatial resolution of ∼1 mm and oxygen resolution of ∼3 torr. The position of the OxyLite track is measured within a few millimeters accuracy using a custom stereotactic positioning device. A total of 17 images involving two tracks each were obtained. Of these, 14 showed excellent correlation in spatial distribution and oxygen magnitude between the Oxylite™ measured pO2 and a track located in the tumor within the uncertainties of the Oyxlite™ localizability. An example of this agreement is shown in the Figure 1. The likely problem with the remaing 3 tracks is the location of the track in the image. The strong correlation of the two modalities corroborates EPR imaging as a useful tool for the study of tumor oxygenation. Figure Oxygen values measured with Oxylite (closed circles) and an EPR oxygen image (open circles)

[Proc Amer Assoc Cancer Res, Volume 46, 2005]