We are developing three independent imaging modalities based on Electron Paramagnetic Resonance (EPR) to extract spatially resolved physiological information such as tumor oxygen perfusion, redox status etc using redox sensitive probes such as the stable nitroxides and oxygen sensitive spin probes such as the triarylmethyl radicals. Project 1: Time-domain EPR Imaging for functional imaging applications. This technique is now implemented for routine functional imaging experiments. We have a) demonstrated the feasibility of obtaining high-resolution images of contrast agent distribution and the oxygen dependent spectral changes of the contrast agent from a live animal. b) Data collection and image reconstruction software have been implemented. c) In vivo images from experimental animals show that it is possible to map tissue oxygen levels and also perfusion of contrast agents. d) Currently developing strategies to shorten the imaging time and increase the detection sensitivity. e) Constructed spectrometers at higher frequencies for high resolution imaging. Project 2: Continuous Wave EPR imaging to image tumor redox status using redox sensitive spin probes. This technique uses contrast agents, which are metabolically reduced depending on tissue reducing equivalents. Any changes in the redox status in the tissue will therefore reflect changes in the redox status. Such changes can be detected and imaged using EPR imaging. a) tested the feasibility and implemented studies in tumor bearing animals. b) developed precursors of spin probes which can report on higher levels of oxidation in an imaging experiment. Project 3: Overhauser enhanced MRI: a) demonstrated the feasibility of mapping tissue oxygen from experimental animals. b) demonstrated the feasibility of imaging fluorine based tracers using OMRI.
