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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

Purpose:
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.

Methods:
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.

Results:
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.

Conclusion:
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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