The Influence of Focal Spot Size on Image Quality

Gt, Benness

doi:10.1111/j.1440-1673.1964.tb00961.x

Cited by 1 publication

(1 citation statement)

References 0 publications

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Section: Ct Referencementioning

confidence: 99%

Foxels for high flux, high resolution computed tomography (foxelct) Using broad x-ray focal spots

Alvare¹,

Gordon²

2017

Radiol Diagn Imaging

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Purpose: In general, there is a reciprocal relationship between the width and flux from an x-ray focal spot (corresponding to spatial resolution and photon noise), so that large focal spots are eschewed in computed tomography (CT) and projection and CT mammography. We wish to overcome this limitation. The goal of foxel based computed tomography (FoxelCT) is to achieve spatial resolution limited by the detector pixel size rather than the focal spot size, and therefore permit the use of much smaller detector pixels and/or larger focal spots in clinical CT. Methods:Rather than using the standard approach of treating the x-ray source as a point, we digitally represent the focal spot as an emission picture consisting of pixels we call foxels (FOcal spot piXELS). Intersections of foxel rays with reconstruction voxels are approximated using the Wu antialiasing line drawing algorithm. All foxel rays in the x-ray light field impinging on a given detector pixel are, in effect, lumped together into a single "passage" or compound ray sum. In this introductory paper noise and other effects that degrade CT are not considered allowing us to demonstrate the upper bound of improvement afforded by the geometry of foxels. The FoxelCT algorithm is a generalization of MART (Multiplicative ART). Results:We show, by simulating a fan beam body scanner configuration, that the loss in resolution versus focal spot size is much slower using foxels compared to the loss when representing the focal spot as a point source. For any given focal spot size, approximating it as a point is always worse than using foxels and furthermore introduces anatomical distortions.Conclusions: Foxels permit the use of larger focal spots and thus greater x-ray photon flux with little loss of resolution. Future scanners could take advantage of foxels to increase the ratio of focal spot size to detector pixel size, via bigger focal spots and/or smaller detector pixels. Existing scanners could be immediately enhanced in image quality via incorporation of foxels in their software. Foxels are applicable to any form of radiological imaging that uses focal spots of finite width, including multisource scanners.

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