a) Wireless coils for implantation: 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. Implantable coils for chronic measurement of MR signals from a region of interest will be preferable if they are miniaturized and without leads. We have designed a wireless coils with a paramagnetic oxygen sensor embedded on it. Signals from the paramagnetic oxygen sensor report on the oxygen level quantitatively from the site of implantation. We have designed such a device, implemented it on a test platform and after suitable optimizations tested its operation in vivo successfully to report on tissue oxygen for a period of weeks from the site of implanataion.. b) Slice Selection EPR imaging: Since the phase memory times of EPR signals last for a few microseconds, it is not possible to use slice selection gradients as in MRI. The ability of using slice selection gradients makes three-dimensional imaging with MRI. For EPR imaging we are compelled to use 3-dimensional imaging by collecting image data in three-dimensional k-space which compromises the temporal resolution. We designed an alternate approach of slice selection EPR Imaging using sinusoidal gradients which can select a slice which can then be phase-encoded in only two-dimensions. This allowed rapid volumetric imaging. We have now implemented this for routine imaging of tumor physiology. This allows interrogating spontaneous dynamic changes of tumor oxygenation.
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