Dynamic intensity normalization using eigen flat fields in X-ray imaging

Nieuwenhove, Vincent Van; Beenhouwer, Jan De; Carlo, Francesco De; Mancini, Lucia; Marone, Federica; Sijbers, Jan

doi:10.1364/oe.23.027975

Cited by 89 publications

(51 citation statements)

References 22 publications

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“…They were normalized by flat field correction [53] to remove image artefacts. A denoising algorithm, VBM3D [54], was applied, followed by background subtraction and segmentation.…”

Section: Image Processing and Quantificationmentioning

confidence: 99%

The effect of powder oxidation on defect formation in laser additive manufacturing

et al. 2019

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Understanding defect formation during laser additive manufacturing (LAM) of virgin, stored, and reused powders is crucial for the production of high quality additively manufactured parts. We investigate the effects of powder oxidation on the molten pool dynamics and defect formation during LAM. We compare virgin and oxidised Invar 36 powder under overhang and layer-by-layer build conditions using in situ and operando X-ray Imaging. The oxygen content of the oxidised powder was found to be ca. 6 times greater (0.343 wt.%) than the virgin powder (0.057 wt.%). During LAM, the powder oxide is entrained into the molten pool, altering the Marangoni convection from an inward centrifugal to an outward centripetal flow. We hypothesise that the oxide promotes pore nucleation, stabilisation, and growth. We observe that spatter occurs more frequently under overhang conditions compared to layer-by-layer conditions. Droplet spatter can be formed by indirect laser-driven gas expansion and by the laser-induced metal vapour at the melt surface. In layer-by-layer build conditions, laser re-melting reduces the pore size distribution and number density either by promoting gas release from keyholing or by inducing liquid flow, partially or completely filling pre-existing pores. We also observe that pores residing at the track surface can burst during laser re-melting, resulting in either 2 formation of droplet spatter and an open pore or healing of the pore via Marangoni flow. This study confirms that excessive oxygen in the powder feedstock may cause defect formation in LAM.

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“…They were normalized by flat field correction [53] to remove image artefacts. A denoising algorithm, VBM3D [54], was applied, followed by background subtraction and segmentation.…”

Section: Image Processing and Quantificationmentioning

confidence: 99%

The effect of powder oxidation on defect formation in laser additive manufacturing

et al. 2019

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“…The planar data are processed by a conventional darkcurrent subtraction and flat-field normalization, whereas for CT scans the projections are normalized using a dynamic flat-field approach based on principal-component analysis of the flat images to compensate for beamintensity variations over long exposures [37]. The normalized projections are (optionally) phase retrieved and reconstructed via a graphics-processing-unit-(GPU-)based filtered back projection with a standard Shepp-Logan filter [38].…”

Section: Data Processing and Reconstructionmentioning

confidence: 99%

Monochromatic Propagation-Based Phase-Contrast Microscale Computed-Tomography System with a Rotating-Anode Source

et al. 2019

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We present an experimental setup for monochromatic propagation-based x-ray phase-contrast imaging based on a conventional rotating-copper-anode source, capable of an integrated flux up to 10 8 photons/s at 8 keV. In our study, the system is characterized in terms of spatial coherence, resolution, contrast sensitivity, and stability. Its quantitativeness is demonstrated by comparing theoretical predictions with experimental data on simple wire phantoms both in planar and computerized-tomography-scan geometries. Application to two biological samples of medical interest shows the potential for bioimaging on the millimeter scale with spatial resolution of the order of 10 μm and contrast resolution below 1%. All the scans are performed within laboratory-compatible exposure times, from 10 min to a few hours, and trade-offs between scan time and image quality are discussed.

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“…Namely, given a 30 Hz frame rate and a window of 2w þ 1 = 11 frames, the gain should not vary significantly for times of the order of 1 s. In addition, the fluctuations of the beam are assumed to be small in the time scale of the acquisition: this requirement is generally fulfilled at the Elettra synchrotron operated in topup mode, where 1 mA of ring current is injected every 20 min, having a baseline of 140 mA at 2.4 GeV. A different approach to the dynamic flat-fielding based on principal component analysis is given by Van Nieuwenhove et al (2015). 2.3.2.…”

Section: Pre-processingmentioning

confidence: 99%

Large-area single-photon-counting CdTe detector for synchrotron radiation computed tomography: a dedicated pre-processing procedure

et al. 2018

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Large-area CdTe single-photon-counting detectors are becoming more and more attractive in view of low-dose imaging applications due to their high efficiency, low intrinsic noise and absence of a scintillating screen which affects spatial resolution. At present, however, since the dimensions of a single sensor are small (typically a few cm), multi-module architectures are needed to obtain a large field of view. This requires coping with inter-module gaps and with close-to-edge pixels, which generally show a non-optimal behavior. Moreover, high-Z detectors often show gain variations in time due to charge trapping: this effect is detrimental especially in computed tomography (CT) applications where a single tomographic image requires hundreds of projections continuously acquired in several seconds. This work has been carried out at the SYRMEP beamline of the Elettra synchrotron radiation facility (Trieste, Italy), in the framework of the SYRMA-3D project, which aims to perform the world's first breast-CT clinical study with synchrotron radiation. An ad hoc data pre-processing procedure has been developed for the PIXIRAD-8 CdTe single-photon-counting detector, comprising an array of eight 30.7 mm × 24.8 mm modules tiling a 246 mm × 25 mm sensitive area, which covers the full synchrotron radiation beam. The procedure consists of five building blocks, namely dynamic flat-fielding, gap seaming, dynamic ring removal, projection despeckling and around-gap equalization. Each block is discussed and compared, when existing, with conventional approaches. The effectiveness of the pre-processing is demonstrated for phase-contrast CT images of a human breast specimen. The dynamic nature of the proposed procedure, which provides corrections dependent upon the projection index, allows the effective removal of time-dependent artifacts, preserving the main image features including phase effects.

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Dynamic intensity normalization using eigen flat fields in X-ray imaging

Cited by 89 publications

References 22 publications

The effect of powder oxidation on defect formation in laser additive manufacturing

The effect of powder oxidation on defect formation in laser additive manufacturing

Monochromatic Propagation-Based Phase-Contrast Microscale Computed-Tomography System with a Rotating-Anode Source

Large-area single-photon-counting CdTe detector for synchrotron radiation computed tomography: a dedicated pre-processing procedure

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