a) a) Novel Pulse sequences for human applications: The EPR imaging system developed in our lab is in routine use for pre-clinical imaging of tumor oxygen status in mouse models of cancer, both as xenografts and orthotopic models. Scaling up of resonant structures to enable imaging larger objects for pO2. For implementation in human studies, it is necessary to develop a signal formation method using low RF levels to comply with FDA regulations. An RF excitation scheme called Frank Pulse Sequence was developed whereby signals can be generated with RF power levels of milliwatt compared to the conventional power of 50 Watts. This was possible by the development of an RF module which delivers pulses of excitation with pseudo-random ordering of the phase and a resonant structure which isolates the excitation and signal reception. We are now in the process of integrating the system for Wireless implantable RF coil/oxygen sensing probe assembly for long term oxygen assessment. A miniature wireless RF coil (4 mm dia) with an embedded paramagnetic solid in a biocompatible polymer has been developed which can be implanted in vivo to test the feasibility of monitoring tissue oxygen at the point of implantation. The implanted RF wireless coil has no leads but can be probed with an external coil which can excite the wireless coil and the paramagnetic probe. Thus this assembly can be implanted chronically at desired sites and oxygen changes can be monitored over periods of weeks/months. Preliminary studies show that a 5-7 fold enhanced sensitivity of detection has been realized. In vivo studies are underway. b) With the improvements in imaging of tumor oxygen dynamics, it was possible to use EPR imaging to: a) monitor the post radiation tumor reoxygenation and b: relationship between tumor oxygenation and glycolysis in tumor xenografts.
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