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Maximally Spaced Projection Sequencing in Electron Paramagnetic Resonance Imaging

g redler

G Redler*, B Epel, HJ Halpern, University of Chicago, Chicago, IL

SU-C-144-7 Sunday 1:00PM - 1:55PM Room: 144

Electron paramagnetic resonance imaging (EPRI) is a projection based imaging modality that noninvasively provides 3D images of absolute oxygen concentration (pO₂) in vivo with excellent spatial and pO₂ resolution. When studying physiologic parameters, such as tissue pO₂, in living animals, the situation is inherently dynamic. This may be due to physical movement during imaging leading to artifacts or physiologically relevant temporal changes in pO₂ (i.e. acute hypoxia). In order to properly study such a dynamic system, improvements in temporal resolution and experimental versatility are necessary.

For projection based imaging, uniformly distributed projections result in efficient use of data for image reconstruction. This has led to the current equal-solid-angle (ESA) spacing of projections for EPRI. However, acquisition sequencing must still be optimized in order to achieve uniformity throughout imaging. An object-independent method for uniform acquisition of projections, using the ESA distribution for the final set of projections, is presented. Each successive projection is selected in such a way as to minimize the electrostatic potential energy between itself and prior projections, when projection direction points are considered to be point charges on the unit sphere.

This maximally spaced projection sequencing (MSPS) method significantly improves image quality for intermediate images reconstructed from incomplete projection sets. This enables useful real-time reconstruction. Additionally, the MSPS method 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 necessary improvements in order to more appropriately image and study physiologic changes in a dynamic system.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by grants from the NIH (P41 EB002034 and R01 CA98575).

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