Optimization-based scatter estimation using primary modulation for computed tomography

Chen, Yi; Song, Ying; Ma, Jingchen; Zhao, Jun

doi:10.1118/1.4958680

Cited by 10 publications

(14 citation statements)

References 22 publications

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“…28,31 One research group has recently proposed an iterative approach to make the primary modulation method more robust. 28 The separation of scatter from primary signals is modeled as an optimization problem with the constraints that the estimated scatter distribution should be smooth and the estimated primary signal should match the premeasured modulation pattern.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

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Local filtration based scatter correction for cone‐beam CT using primary modulation

Zhu

2016

Medical Physics

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Purpose: Excessive scatter contamination fundamentally limits the image quality of cone-beam CT (CBCT), hindering its quantitative use in clinical applications. The author has previously proposed an effective scatter correction method for CBCT using primary modulation. A Fourier transform-based algorithm (FTPM) was implemented to estimate scatter from modulated projections, with a few limitations including the assumption of uniform modulation frequency and magnitude that becomes less accurate in the presence of beam-hardening and other nonideal effects. This paper aims to overcome the above drawbacks by developing a new algorithm for the primary modulation method with improved accuracy and reliability. Methods: Incident x-ray intensities for each detector pixel with and without the interception of the modulator blocker are estimated from a modulated flat-field image. A new signal relationship is then developed to obtain a first scatter estimate from a modulated projection using a spatially varying modulation distribution. The method empirically adjusts the effective modulation magnitude for each projection ray to account for the beam-hardening effects. Estimated scatter signals with high expected errors are discarded in the generation of the final scatter distribution. The author proposes a technique of local filtration to accelerate major portions of the signal processing, and the new algorithm is referred to as local filtration based primary modulation (LFPM). Results: The study on the Catphan® 600 phantom shows that LFPM effectively removes scatterinduced cupping artifacts on CBCT images and reduces the CT image error from 222 to 15 HU. In addition, the image contrast on eight contrast rods of the phantom is enhanced by a factor of 2 on average. On an anthropomorphic head phantom, LFPM reduces the CT image error from 153 to 18 HU and eliminates the streak artifacts observed on the result of FTPM with substantially improved image uniformity. On the Rando® phantom, LFPM reduces the CT image error from 278 to 4 HU around the object center. Conclusions: As compared with the previously developed FTPM algorithm, LFPM enhances the imaging performance by using a more flexible data processing framework that does not require projection data downsampling or uniform modulation frequency and magnitude. It also becomes possible to discard suspicious scatter estimate values prior to the generation of a final scatter distribution and to model the beam-hardening effects on modulation for improved scatter estimation accuracy. The presented research further exploits the potential of the primary modulation method on scatter correction and facilitates its clinical adoption in CBCT imaging. C 2016 American Association of Physicists in Medicine. [http://dx

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Section: Conclusion and Discussionmentioning

confidence: 99%

“…Despite its theoretical elegance and success as demonstrated in a few publications by different research groups, [6][7][8][9][10]26,27,31 however, several limitations should be noted on FTPM. First, FTPM requires projections to be downsampled for signal processing.…”

Section: A2 Limitations Of the Ftpm Methodsmentioning

confidence: 99%

Local filtration based scatter correction for cone‐beam CT using primary modulation

Zhu

2016

Medical Physics

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“…Many methods have been proposed and developed for determining the spatial distribution of scatter in CBCT including: measurements using beam-stopper-array [9], moving blocker [10] or primary modulator [11]; Monte Carlo simulations with optimized code package [12] [13], or GPU-based high computational efficiency platform [14] [15]; and analytical calculations with projection-based pencil-beam-scatter-kernel (PBSK) models [16] [17], or image-based single scatter calculation combined with multiple scatter estimation [5] [6] [7] [18] [19]. For In this study, we propose an analytical model to calculate the spatial distribution dominant CSS component of the PBSK aiming to improve the computational accuracy of the PBSK based superposition method for scatter correction.…”

Section: Introductionmentioning

confidence: 99%

Analytical Calculation of the Compton Single Scatter Component of Pencil Beam Scatter Kernel for Scatter Correction in kV Cone Beam CT (kV-CBCT)

Liu¹,

Bourland²

2018

IJMPCERO

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The accuracy of conventional superposition or convolution methods for scatter correction in kV-CBCT is usually compromised by the spatial variation of pencil-beam scatter kernel (PBSK) due to finite size, irregular external contour and heterogeneity of the imaged object. This study aims to propose an analytical method to quantify the Compton single scatter (CSS) component of the PBSK, which dominates the spatial distribution of total scatter assuming that multiple scatter can be estimated as a constant background and Rayleigh scatter is the secondary source of scatter. The CSS component of PBSK is the line integration of scatter production by incident primary photons along the beam line followed by the post-scattering attenuation as the scattered photons traverse the object. We propose to separate the object-specific attenuation term from the line integration and equivalently replace it with an average value such that the line integration of scatter production is object independent but only beam specific. We derived a quartic function formula as an approximate solution to the spatial distribution of the unattenuated CSS component of PBSK. The "effective scattering center" is introduced to calculate the average attenuation. The proposed analytical framework to calculate the CSS was evaluated using parameter settings of the On-Board Imager kV-CBCT system and was found to be in high agreement with the reference results. The proposed method shows highly increased computational efficiency compared to conventional analytical calculation methods based on point scattering model. It is also potentially useful for correcting the spatial variant PBSK in adaptive superposition method.

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“…The other one assumes that a properly scatter-corrected image is free of the additional intensity variations introduced by the modulator. 4,8 If the assumption is true, minimizing the total variation of the estimated primary with respect to the estimated scatter will provide the right scatter values. However, there is a tradeoff between the smoothness of the primary and the scatter components.…”

Section: Introductionmentioning

confidence: 99%

“…The purpose of this study is to evaluate the performance of these methods (except for Ref. 8 as it was published right before the acceptance of this paper), propose several improvements, and analyze the effect of their parameters. This paper addresses numerous issues related to primary modulation, such as blurred modulator edges and spatially varying effective transmission factors, detector backscatter, and sensibility to image textures.…”

Section: Introductionmentioning

confidence: 99%

Analysis of primary modulation based x‐ray scatter correction methods

2016

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Optimization-based scatter estimation using primary modulation for computed tomography

Abstract: The proposed OSE algorithm improves the robustness and accuracy in scatter estimation and correction. This method is promising for scatter correction of various kinds of x-ray imaging modalities, such as x-ray radiography, cone beam CT, and the fourth-generation CT.

Cited by 10 publications

References 22 publications

Local filtration based scatter correction for cone‐beam CT using primary modulation

Local filtration based scatter correction for cone‐beam CT using primary modulation

Analytical Calculation of the Compton Single Scatter Component of Pencil Beam Scatter Kernel for Scatter Correction in kV Cone Beam CT (kV-CBCT)

Analysis of primary modulation based x‐ray scatter correction methods

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