Program Information
Impact of Focal Spot and Detector Rotation On Spatial Resolution in MDCT
A Budde1,2*, J Hsieh2 , G Chen1 , (1) University of Wisconsin-Madison, Madison, WI, (2) GE Healthcare
Presentations
TH-EF-601-8 (Thursday, August 3, 2017) 1:00 PM - 3:00 PM Room: 601
Purpose: The spatial resolution in CT images varies with image location. Although the MTF at the isocenter of CT images is well modeled, a quantitative model of the physical factors that impact the off-isocenter resolution variation in CT has been elusive. In this work, the root cause of one of these effects, the motion of the focal spot and detector within a single projection acquisition, is modeled and its impact on a physical system is quantitatively studied.
Methods: First, a cascaded systems model analysis was developed to study the impact of focal spot and detector motion at a given image location. The physical factors, such as image location, the number of projections per rotation, and the direction of spatial resolution measurement, are included in the cascaded systems model analysis. Based upon the model analysis, the impact of focal spot and detector motion on spatial resolution was analytically derived. The derived analytical results were then experimentally verified with measurements on a physical CT system. Since image space MTF measurement is confounded with other spatially variant effects, such as magnification, rebinning, and/or backprojection, projection space MTF measurements were taken, which compare the change in resolution between a static gantry and a moving gantry in order to isolate the effect of focal spot and detector motion.
Results: The resolution degradation due to focal spot and detector motion measured on a physical system matched the modeled resolution degradation closely across varied distance to isocenters, views per rotation, and measurement directions.
Conclusion: In this work, a quantitative model of the resolution variation due to focal spot and detector motion within a projection acquisition was created and then validated with experimental results. This work allows for improved understanding of the mechanisms behind off-isocenter resolution degradation, permitting improved clinical scan protocol optimization or algorithmic correction.
Funding Support, Disclosures, and Conflict of Interest: Research partially supported by GE Healthcare. Employee, GE Healthcare.
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