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ABSTRACT Electron paramagnetic resonance imaging (EPRI) provides 3D images of absolute oxygen concentration (pO2) in vivo with excellent spatial and pO2 resolution. When investigating such physiologic parameters in living animals, the situation is inherently dynamic. Improvements in temporal resolution and experimental versatility are necessary to properly study such a system. Uniformly distributed projections result in efficient use of data for image reconstruction. This has dictated current methods such as equal-solid-angle (ESA) spacing of projections. However, acquisition sequencing must still be optimized to achieve uniformity throughout imaging. An object-independent method for uniform acquisition of projections, using the ESA uniform distribution for the final set of projections, is presented. Each successive projection maximizes the distance in the gradient space between itself and prior projections. This maximally spaced projection sequencing (MSPS) method improves image quality for intermediate images reconstructed from incomplete projection sets, enabling useful real-time reconstruction. This method also provides improved experimental versatility, reduced artifacts, and the ability to adjust temporal resolution post factum to best fit the data and its application. The MSPS method in EPRI provides the improvements necessary to more appropriately study a dynamic system. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 33-45, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT The importance of tissue oxygenation has led to a great interest in methods for imaging pO2 in vivo. Electron paramagnetic resonance imaging (EPRI) provides noninvasive, near absolute 1 mm-resolved 3D images of pO2 in the tissues and tumors of living animals. Current EPRI image reconstruction methods tend to be time consuming and preclude real-time visualization of information. Methods are presented to significantly accelerate the reconstruction process in order to enable real-time reconstruction of EPRI pO2 images. These methods are image reconstruction using graphics processing unit (GPU)-based 3D filtered back-projection and lookup table parameter fitting. The combination of these methods leads to acceleration factors of over 650 compared to current methods and allows for real-time reconstruction of EPRI images of pO2 in vivo. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 46-57, 2015 [ABSTRACT FROM AUTHOR]

Abstract: A simple scheme for dynamically switching the quality factor, Q, of a loop‐gap resonator (LGR); working at 250 MHz is presented. The addition of this Q‐modulator resulted in 30% improvement in electron paramagnetic resonance imager signal‐to‐noise ratio. During pulse excitation, this scheme lowered the Q, while higher Q was obtained during signal detection. These conditions favored the image acquisition. The Q‐modulator is passive; the transition between different states was actuated by the radio frequency power itself. [ABSTRACT FROM AUTHOR]