SELECTED PROJECTS
Project |01
Hybrid MR based Coimaging System
Electron paramagnetic resonance imaging (EPRI) is a powerful technique that enables spatial mapping of free radicals or other paramagnetic compounds; however, it does not in itself provide anatomic visualization of the body. Proton magnetic resonance imaging (MRI) is well suited to provide anatomical visualization. A hybrid EPR/NMR coimaging instrument was constructed that utilizes the complementary capabilities of both techniques, su-perimposing EPR and proton-MR images to provide the distri-bution of paramagnetic species in the body. A common magnet and field gradient system is utilized along with a dual EPR and proton-NMR resonator assembly, enabling coimaging without the need to move the sample. EPRI is performed at 1.2 GHz/ 40 mT and proton MRI is performed at 16.18 MHz/380 mT; hence the method is suitable for whole-body coimaging of living mice. The gradient system used is calibrated and controlled in such a manner that the spatial geometry of the two acquired images is matched, enabling their superposition without additional postprocessing or marker registration. The performance of the system was tested in a series of phantoms and in vivo applications by mapping the location of a paramagnetic probe in the gastrointestinal (GI) tract of mice. This hybrid EPR/NMR coimaging instrument enables imaging of paramagnetic molecules along with their anatomic localization in the body.
Key words: proton MRI; EPR imaging; free radicals, oxygen; image coregistration; in vivo NMR; in vivo EPR
Project |02
Proton Electron Double Resonance based spectroscopy and imaging
Dynamic nuclear polarization (DNP) is an NMR-based technique which enables detection and spectral
characterization of endogenous and exogenous paramagnetic substances measured via transfer of polarization from the saturated unpaired electron spin system to the NMR active nuclei. A variable field system capable of performing DNP spectroscopy with NMR detection at any magnetic field in the range 0–0.38 T is described. The system is built around a clinical open-MRI system. To obtain EPR spectra via DNP, partial cancellation of the detection field is required to alter the evolution field at which the EPR excitation is achieved. A description of the primary magnet, cancellation coils, power supplies, interfacing hardware, RF electronics and console are included. Performance of the instrument has been evaluated by acquiring DNP spectra of phantoms with aqueous nitroxide solutions (TEMPOL) at three NMR detection fields of 97 G, 200 G and 587 G and fixed EPR evolution field of 100 G corresponding to an irradiation frequency of 282.3 MHz.
Keywords: Proton MRI; EPR imaging; Free radicals; Oxygen; Image co-registration; In vivo NMR;
In vivo EPR; Overhauser effect
Project |03
In vivo multisite oximetry using MR based coimaging
Coimaging employing electron paramagnetic resonance (EPR) imaging and MRI is used for rapid in vivo oximetry conducted simultaneously across multiple organs of a mouse. A recently developed hybrid EPR–NMR coimaging instrument is used for both EPR and NMR measurements. Oxygen sensitive particulate EPR probe is implanted in small localized pockets, called sites, across multiple regions of a live mouse. Three dimensional MRI is used to generate anatomic visualization, providing precise locations of implant sites. The pO2 values, one for every site, are then estimated from EPR measurements. To account for radio frequency (RF) phase inhomogeneities inside a large resonator carrying a lossy sample, a generalization of an existing EPR data model is proposed. Utilization of known spectral lineshape, sparse distribution, and known site locations reduce the EPR data collection by more than an order of magnitude over a conventional spectral–spatial imaging, enhancing the feasibility of in vivo EPR oximetry for clinically relevant models.
Keywords: EPR; EPRI; MRI; Coimaging; Oximetry;Multisite
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