Evaluation of scatter mitigation strategies for x-ray cone-beam CT: impact of scatter subtraction and anti-scatter grids on contrast-to-noise ratio

Dimitrios Lazos; Giovanni Lasio; Joshua D. Evans; Jeffrey F. Williamson

doi:10.1117/12.713610

13 March 2007 Evaluation of scatter mitigation strategies for x-ray cone-beam CT: impact of scatter subtraction and anti-scatter grids on contrast-to-noise ratio

Dimitrios Lazos, Giovanni Lasio, Joshua D. Evans, Jeffrey F. Williamson

Author Affiliations +

Proceedings Volume 6510, Medical Imaging 2007: Physics of Medical Imaging; 65101V (2007) https://doi.org/10.1117/12.713610
Event: Medical Imaging, 2007, San Diego, CA, United States

Abstract

The large contribution of scatter to cone-beam computed tomography (CBCT) x-ray projections significantly degrades image quality, both through streaking and cupping artifacts and by loss of low contrast boundary detectability. The goal of this investigation is to compare the efficacy of three widely used scatter mitigation methods: subtractive scatter correction (SSC); anti-scatter grids (ASG); and beam modulating with bowtie filters; for improving signal-to-noise ratio (SNR), contrast, contrast-to-noise ratio (CNR) and cupping artifacts. A simple analytic model was developed to predict scatter-to-primary ratio (SPR) and CNR as a function of cylindrical phantom thickness. In addition, CBCT x-ray projections of a CatPhan QA phantom were measured, using a Varian CBCT imaging system, and computed, using an inhouse Monte Carlo photon-transport code to more realistically evaluate the impact of scatter mitigation techniques. Images formed with uncorrected sinograms acquired without ASGs and bow-tie filter show pronounced cupping artifacts and loss of contrast. Subtraction of measured scatter profiles restores image uniformity and CT number accuracy, but does not improve CNR, since the improvement in contrast almost exactly offset by the increase in relative x-ray noise. ASGs were found to modestly improve CNR (up to 20%, depending ASG primary transmission and selectivity) only in body scans, while they can reduce CNR for head phantoms where SPR is low.

Citation Download Citation

Dimitrios Lazos, Giovanni Lasio, Joshua D. Evans, and Jeffrey F. Williamson "Evaluation of scatter mitigation strategies for x-ray cone-beam CT: impact of scatter subtraction and anti-scatter grids on contrast-to-noise ratio", Proc. SPIE 6510, Medical Imaging 2007: Physics of Medical Imaging, 65101V (13 March 2007); https://doi.org/10.1117/12.713610

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