Continuous Wave Electron Paramagnetic Resonance Imaging

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Project 3: Continuous Wave Electron Paramagnetic Resonance Imaging.Instrumentation: The current spectrometer is an analog spectrometer which is operational at 300 and 750 MHz. Most components are analog devices which have their own contributions to noise and artifacts which will compromise the signal:noise ratio. DSP (digital signal processing) technology is increasingly being used in modern telecommunication systems as well as consumer electronics and cost of these modules has become small. The noise associated with several analog components in RF electronics can be avoided by relying on DSP strategies where possible. We plan to develop a general EPR spectrometer platform based on DSP strategy to confer versatility in operation with a nominal operating frequency of 750 MHz during the initial phase. Subsequent to this, we plan to incorporate capabilities in the spectrometer to operate at 300 MHz as well. In the proposed system, detection schemes such as direct detection with rapid scan as well as phase-sensitive detection using ac modulation of the dc magnetic field can be integrated. This system will use digital synthesizers to generate all RF and control signals and a 'Software Radio' based receiver. Three major components of this system: RF source, receiver and magnetic field controller are under various stages of development. Applications: The strength of this technique in detecting phenotypic changes of genetically modified animals is demonstrated by the studies using wild type and Thrombospondin-1 null mice with surgical wounds in the skin flap. TSP-1 is a putative antagonist of perfusion and tissue survival and can limit survival of soft tissue following surgery. This hypothesis was tested using oxygen sensing paramagnetic solid probes at proximal and distal sites to the wound on the skin flap and the tissue pO2 was monitored using EPR spectroscopy. EPR studies, histological analysis and western blot analysis on wild type and TSP-1 null mice showed that endogenous TSP-1 was inhibitory to the vascular smooth muscle relaxation by nitric oxide.Other studies examined the effect of core body temperature in mice on the pO2 values in muscle and mammary tissue using chronically implanted oxygen sensing solid paramagnetic particles whose oxygen dependent spectral line widths were monitored over a period of 4 weeks. The studies showed that the femoral muscles function at higher pO2 than the mammary fat pad and also indicated the importance of maintaining core body temperature for valid monitoring of physiology.Experimental Subjects:Neither human subjects nor human tissues.