Limitations of anti-scatter grids when used with high resolution image detectors

Singh, Vivek Kumar; Jain, Amit; Bednarek, Daniel R.; Rudin, Stephen

doi:10.1117/12.2043063

Cited by 11 publications

(15 citation statements)

References 9 publications

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“…Studies previously reported by us involved a simulated artery block phantom with a uniform frontal head equivalent phantom used as the scattering source to investigate the effectiveness of the method to remove the anti-scatter grid-line artifacts when a grid is used with a Flat Panel Detector (FPD) and high resolution CMOS detector 6, 7 .…”

Section: Methodsmentioning

confidence: 99%

Scatter estimation and removal of anti-scatter grid-line artifacts from anthropomorphic head phantom images taken with a high resolution image detector

et al. 2016

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In radiography, one of the best methods to eliminate image-degrading scatter radiation is the use of anti-scatter grids. However, with high-resolution dynamic imaging detectors, stationary anti-scatter grids can leave grid-line shadows and moiré patterns on the image, depending upon the line density of the grid and the sampling frequency of the x-ray detector. Such artifacts degrade the image quality and may mask small but important details such as small vessels and interventional device features. Appearance of these artifacts becomes increasingly severe as the detector spatial resolution is improved. We have previously demonstrated that, to remove these artifacts by dividing out a reference grid image, one must first subtract the residual scatter that penetrates the grid; however, for objects with anatomic structure, scatter varies throughout the FOV and a spatially differing amount of scatter must be subtracted. In this study, a standard stationary Smit-Rontgen X-ray grid (line density - 70 lines/cm, grid ratio - 13:1) was used with a high-resolution CMOS detector, the Dexela 1207 (pixel size - 75 micron) to image anthropomorphic head phantoms. For a 15 × 15cm FOV, scatter profiles of the anthropomorphic head phantoms were estimated then iteratively modified to minimize the structured noise due to the varying grid-line artifacts across the FOV. Images of the anthropomorphic head phantoms taken with the grid, before and after the corrections, were compared demonstrating almost total elimination of the artifact over the full FOV. Hence, with proper computational tools, anti-scatter grid artifacts can be corrected, even during dynamic sequences.

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Section: Methodsmentioning

confidence: 99%

Scatter estimation and removal of anti-scatter grid-line artifacts from anthropomorphic head phantom images taken with a high resolution image detector

et al. 2016

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“…Also, we are using a 20 × 20 cm beam size at the detector in this study (which is different than our previously reported study 9 done at 15 × 15 cm beam size) as 20 × 20 cm looks forward to a future of larger high resolution detectors. A previously reported study involved a standard flat panel detector (FPD) with less resolution (194 μm pixels) and hence grid-line artifacts were less prominent 9 .…”

Section: Methodsmentioning

confidence: 91%

“…A previously reported study involved a standard flat panel detector (FPD) with less resolution (194 μm pixels) and hence grid-line artifacts were less prominent 9 .…”

Section: Methodsmentioning

confidence: 99%

“…In order to keep the filtration of the x-ray beam the same, the scatter free images (set-ups 1 and 4) are taken with the featureless part of the artery block in the phantom slot. All the images were flat-field and offset corrected and the table was always in the beam requiring care to eliminate not only the gridlines but also blotches in the images caused by table structure 9 .…”

Section: Methodsmentioning

confidence: 99%

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Anti-scatter grid artifact elimination for high resolution x-ray imaging CMOS detectors

et al. 2015

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Higher resolution in dynamic radiological imaging such as angiography is increasingly being demanded by clinicians; however, when standard anti-scatter grids are used with such new high resolution detectors, grid-line artifacts become more apparent resulting in increased structured noise that may overcome the contrast signal improvement benefits of the scatter-reducing grid. Although grid-lines may in theory be eliminated by dividing the image of a patient taken with the grid by a flat-field image taken with the grid obtained prior to the clinical image, unless the remaining additive scatter contribution is subtracted in real-time from the dynamic clinical image sequence before the division by the reference image, severe grid-line artifacts may remain. To investigate grid-line elimination, a stationary Smit Röntgen X-ray grid (line density: 70 lines/cm, grid ratio 13:1) was used with both a 75 micron-pixel CMOS detector and a standard 194 micron-pixel flat panel detector (FPD) to image an artery block insert placed in a modified uniform frontal head phantom for a 20 × 20cm FOV (approximately). Contrast and contrast-to-noise ratio (CNR) were measured with and without scatter subtraction prior to grid-line correction. The fixed pattern noise caused by the grid was substantially higher for the CMOS detector compared to the FPD and caused a severe reduction of CNR. However, when the scatter subtraction corrective method was used, the removal of the fixed pattern noise (grid artifacts) became evident resulting in images with improved CNR.

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“…The use of conventional grids with these detectors can result in increased structure noise due to the finite thickness of grid lines. [1] Use of a smaller field of view is another option but this limits the usefulness of large field of view detectors and scanned beams are not practical for real-time imaging.…”

Section: Introductionmentioning

confidence: 99%

Scatter reduction for high resolution image detectors with a region of interest attenuator

Jain¹,

Bednarek²,

Rudin³

2014

SPIE Proceedings

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Compton scatter is the main interaction of x-rays with objects undergoing radiographic and fluoroscopic imaging procedures. Such scatter is responsible for reducing image signal to noise ratio which can negatively impact object detection especially for low contrast objects. To reduce scatter, possible methods are smaller fields-of-view, larger air gaps and the use of an anti-scatter grid. Smaller fields of view may not be acceptable and scanned-beam radiography is not practical for real-time imaging. Air gaps can increase geometric unsharpness and thus degrade image resolution. Deployment of an anti-scatter grid is not well suited for high resolution imagers due to the unavailability of high line density grids needed to prevent grid-line artifacts. However, region of interest (ROI) imaging can be used not only for dose reduction but also for scatter reduction in the ROI. The ROI region receives unattenuated x-rays while the peripheral region receives x-rays reduced in intensity by an ROI attenuator. The scatter within the ROI part of the image originates from both the unattenuated ROI and the attenuated peripheral region. The scatter contribution from the periphery is reduced in intensity because of the reduced primary x-rays in that region and the scatter fraction in the ROI is thus reduced. In this study, the scatter fraction for various kVp’s, air-gaps and field sizes was measured for a uniform head equivalent phantom. The scatter fraction in the ROI was calculated using a derived scatter fraction formula, which was validated with experimental measurements. It is shown that use of a ROI attenuator can be an effective way to reduce both scatter and patient dose while maintaining the superior image quality of high resolution detectors.

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Limitations of anti-scatter grids when used with high resolution image detectors

Cited by 11 publications

References 9 publications

Scatter estimation and removal of anti-scatter grid-line artifacts from anthropomorphic head phantom images taken with a high resolution image detector

Scatter estimation and removal of anti-scatter grid-line artifacts from anthropomorphic head phantom images taken with a high resolution image detector

Anti-scatter grid artifact elimination for high resolution x-ray imaging CMOS detectors

Scatter reduction for high resolution image detectors with a region of interest attenuator

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