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Proceedings Paper

Evaluation of an erbium modulator in x-ray scatter correction using primary modulation
Author(s): Hewei Gao; Tianye Niu; Lei Zhu; Rebecca Fahrig
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Paper Abstract

A primary modulator made of erbium is evaluated in X-ray scatter correction using primary modulation. Our early studies have shown that erbium is the optimal modulator material for an X-ray cone-beam computed tomography (CBCT) system operated at 120 kVp, exhibiting minimum beam hardening which otherwise weakens the modulator's ability to separate scatter from primary. In this work, the accuracy of scatter correction is compared for two copper modulators (105 and 210 μm of thickness) and one erbium modulator (25.4 μm of thickness) with the same modulation frequencies. The variations in the effective transmission factors of these three modulators as functions of object filtrations are first measured to show the magnitudes of beam hardening caused by the modulators themselves. Their scatter correction performances are then tested using a Catphan©600 phantom on our tabletop CBCT system. With and without 300 μm of copper in the beam, the measured variations for these three modulators are 4.3%, 7.8%, and 0.9%, respectively. Using the 105- and 210-μm copper modulators, our scatter correction method reduces the average CT number error from 327.3 Hounsfield units (HU) to 19.4 and 20.9 HU in the selected regions of interest, and enhances the contrast-to-noise ratio (CNR) from 10.7 to 16.5 and 15.9, respectively. With the 25.4-μm erbium modulator, the CT number error is markedly reduced to 2.8 HU and the CNR is further increased to 17.4.

Paper Details

Date Published: 16 March 2011
PDF: 12 pages
Proc. SPIE 7961, Medical Imaging 2011: Physics of Medical Imaging, 796122 (16 March 2011); doi: 10.1117/12.878609
Show Author Affiliations
Hewei Gao, Stanford Univ. (United States)
Tianye Niu, Georgia Institute of Technology (United States)
Lei Zhu, Georgia Institute of Technology (United States)
Rebecca Fahrig, Stanford Univ. (United States)


Published in SPIE Proceedings Vol. 7961:
Medical Imaging 2011: Physics of Medical Imaging
Norbert J. Pelc; Ehsan Samei; Robert M. Nishikawa, Editor(s)

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