Simultaneous scatter rejection and correction method using 2D antiscatter grids for CBCT

Yu, Zhelin; Park, Yeonok; Altunbas, Cem

doi:10.1117/12.2549763

Cited by 10 publications

(37 citation statements)

References 10 publications

(13 reference statements)

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“…A final issue is the suppression of image artifacts induced by 2D ASG's septal shadows or footprint. Our prior work 23,24,40 on grid-induced artifact suppression provided promising results, and can help to address this challenge.…”

Section: Discussionmentioning

confidence: 98%

“…To evaluate the effect of residual scatter correction on image quality, CBCT scans with 2D ASGs were corrected using the GSS method. 23,24 As described in Section 2.C, the GSS method employs the 2D ASG's septal shadows to measure and correct residual scatter in projections, and thus, it was not used for the ASG-free and 1D ASG configurations. Apart from residual scatter correction, no other postprocessing steps (such as beam hardening or image lag correction) were applied to the 2D ASG CBCT scans.…”

Section: B Experiments Setup and Image Quality Evaluationsmentioning

confidence: 99%

“…A detailed description of the method can be found in other publications. 23,24 When a 2D ASG is on the FPD, primary x rays incident on the grid septa are stopped, and the primary signal intensity is reduced in pixels underneath grid septa (or in septal shadows). Compared to primary x rays, scattered x rays transmitted through the grid exhibit a different distribution due to their relatively broad angle of incidence on the detector.…”

Section: C Overview Of Grid-based Scatter Samplingmentioning

confidence: 99%

“…The new scatter correction method, referred to as grid-based scatter sampling (GSS), utilizes a 2D ASG to measure and correct residual scatter intensity. 23,24 In essence, this approach expands the role of 2D ASG from that of a scatter rejection device to a scatter measurement and correction device. Our proof-of-concept work on the GSS method 23,24 indicated that further improvement in CT number accuracy could be achieved by correcting residual scatter.…”

Section: Introductionmentioning

confidence: 99%

“…23,24 In essence, this approach expands the role of 2D ASG from that of a scatter rejection device to a scatter measurement and correction device. Our proof-of-concept work on the GSS method 23,24 indicated that further improvement in CT number accuracy could be achieved by correcting residual scatter. That work described the underlying principles and implementation of GSS method; however, the utility of this method under different 2D ASG grid ratios has not been investigated.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of scatter rejection and correction performance of 2D antiscatter grids in cone beam computed tomography

et al. 2021

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We have been investigating two-dimensional (2D) antiscatter grids (2D ASGs) to reduce scatter fluence and improve image quality in cone beam computed tomography (CBCT). In this work, two different aspects of 2D ASGs, their scatter rejection and correction capability, were investigated in CBCT experiments. To correct residual scatter transmitted through the 2D ASG, it was used as a scatter measurement device with a novel method: grid-based scatter sampling. Methods: Three focused 2D ASG prototypes with grid ratios of 8, 12, and 16 were developed for linac-mounted offset detector CBCT geometry. In the first phase, 2D ASGs were used as a scatter rejection device, and the effect of grid ratio on CT number accuracy and contrast-to-noise ratio (CNR) evaluated in CBCT images. In the second phase, a grid-based scatter sampling method which exploits the signal modulation characteristics of the 2D ASG's septal shadows to measure and correct residual scatter transmitted through the grid was implemented. To evaluate CT number accuracy, the percent change in CT numbers was measured by changing the phantom from head to pelvis size and configuration. Results: When 2D ASG was used as a scatter rejection device, CT number accuracy increased and the CT number variation due to change in phantom dimensions was reduced from 23% to 2-6%. A grid ratio of 16 yielded the lowest CT number variation. All three 2D ASGs yielded improvement in CNR, up to a factor of two in pelvis-sized phantoms. When 2D ASG prototypes were used for both scatter rejection and correction, CT number variations were reduced further, to 1.3-2.6%. In comparisons with a clinical CBCT system and a high-performance radiographic ASG, 2D ASG provided higher CT number accuracy under the same imaging conditions. Conclusions: When 2D ASG is used solely as a scatter rejection device, substantial improvement in CT number accuracy can be achieved by increasing the grid ratio. Two-dimensional ASGs also provided significant CNR improvement even at lower grid ratios. Two-dimensional ASGs used in conjunction with the grid-based scatter sampling method provided further improvement in CT number accuracy, irrespective of the grid ratio, while preserving 2D ASGs' capacity to improve CNR. The combined effect of scatter rejection and residual scatter correction by 2D ASG may accelerate implementation of new techniques in CBCT that require high quantitative accuracy, such as radiotherapy dose calculation and dual energy CBCT.

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Section: Discussionmentioning

confidence: 98%

Section: B Experiments Setup and Image Quality Evaluationsmentioning

confidence: 99%

Section: C Overview Of Grid-based Scatter Samplingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evaluation of scatter rejection and correction performance of 2D antiscatter grids in cone beam computed tomography

et al. 2021

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A novel grid regression demodulation method for radiographic grid artifact correction

Yu¹,

Wang

2021

Medical Physics

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In x-ray radiography, the commonly used antiscatter grid for enhancing image quality causes artifacts in the form of periodic noises, such as shadows, cutoff, and Moiré fringes. Software degridding is traditionally performed via linear or homomorphic filtering in the spectral domain. These methods inevitably result in image blurring, information loss, and distortion, thus hindering detection and assessment of diseases. We seek effective and practical solutions for grid artifact correction based on spatial-domain analysis toward high-quality imaging. Methods: By analyzing the physical process of grid artifact formation, we track down the root of the problem associated with spectral filtering. We propose the grid regression demodulation (GRD). The degridding cost is forged as a functional of the latent x-ray photon image and parametric grid model characterizing grid transmission property. Regularization on the grid spectra is incorporated. We devise optimization algorithms for artifact correction and grid pattern estimation. GRD decouples the partially overlapped spectra of the grid and anatomy, and removes the artifacts independently, thus restoring the underlying clinically relevant data.Results: Method efficacy is demonstrated using simulated and real data. GRD effectively preserves image edges, textures, and patterns while removing grid artifacts. For the known ground truth setting, GRD gives a near-perfect correction. For real data, GRD is capable of correcting not only the primary grid artifacts, but also the higher grid harmonic artifacts while keeping image content unaltered, which is unachievable by the other methods. Our method has low residual errors and exhibits a successful demodulation effect without introducing additional artifacts, while ringing or cilia artifacts are present in the others. Conclusions: The proposed method outperforms the prevalent transform techniques for correcting grid artifacts in digital radiography. It is self-sustained and self-adaptive to a range of targets and beam quality. Our approach is advantageous in restoring the latent image while suppressing grid noises. It retrieves the true scale factor of the degridded data, which is unattainable via any spectral filtering techniques. This work unlocks a promising venue to improve and upgrade low-dose medical radiographic imaging technology.

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3D‐printed large‐area focused grid for scatter reduction in cone‐beam CT

et al. 2022

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Background: Cone-beam computed tomography (CBCT) systems acquire volumetric data more efficiently than fan-beam or multislice CT, particularly when the anatomy of interest resides within the axial field-of -view of the detector and data can be acquired in one rotation. For such systems, scattered radiation remains a source of image quality degradation leading to increased noise, image artifacts, and CT number inaccuracies. Purpose: Recent advances in metal additive manufacturing allow the production of highly focused antiscatter grids (2D-ASGs) that can be used to reduce scatter intensity, while preserving primary radiation transmission. We present the first implementation of a large-area, 2D-ASG for flat-panel CBCT, including grid-line artifact removal and related improvements in image quality. Methods: A 245 × 194 × 10 mm 2D-ASG was manufactured from chromecobalt alloy using laser powder-bed fusion (LPBF) (AM-400; Renishaw plc, New Mills Wotton-under-Edge, UK). The 2D-ASG had a square profile with a pitch of 9.09 lines/cm and 10:1 grid-ratio. The nominal 0.1 mm grid septa were focused to a 732 mm x-ray source to optimize primary x-ray transmission and reduce grid-line shadowing at the detector. Powder-bed fusion ensured the structural stability of the ASG with no need for additional interseptal support. The 2D-ASG was coupled to a 0.139-mm element pitch flat-panel detector (DRX 3543, Carestream Health) and proper alignment was confirmed by consistent grid-line shadow thickness across the whole detector array. A 154-mm diameter CBCT image-quality-assurance phantom was imaged using a rotary stage and a ceiling-mounted, x-ray unit (Proteus XR/a, GE Medical Systems, 80kVp, 0.5mAs). Grid-line artifacts were removed using a combination of exposuredependent gain correction and spatial-frequency, Fourier filtering. Projections were reconstructed using a Parker-weighted, FDK algorithm and voxels were spatially averaged to 357 × 357 × 595 µm to improve the signal-to-noise characteristics of the CBCT reconstruction. Finally, in order to compare image quality with and without scatter, the phantom was scanned again under the same CBCT conditions but with no 2D-ASG. No additional antiscatter (i.e., air-gap, bowtie filtration) strategies were used to evaluate the effects in image quality caused by the 2D-ASG alone. Results: The large-area, 2D-ASG prototype was successfully designed and manufactured using LPBF. CBCT image-quality improvements using the 2D-ASG included: an overall 14.5% CNR increase across the volume; up to 48.8% CNR increase for low-contrast inserts inside the contrast plate of the QA phantom; and a 65% reduction of cupping artifact in axial profiles of water-filled cross sections of the phantom. Advanced image processing strategies to remove grid 240

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Simultaneous scatter rejection and correction method using 2D antiscatter grids for CBCT

Cited by 10 publications

References 10 publications

Evaluation of scatter rejection and correction performance of 2D antiscatter grids in cone beam computed tomography

Evaluation of scatter rejection and correction performance of 2D antiscatter grids in cone beam computed tomography

A novel grid regression demodulation method for radiographic grid artifact correction

3D‐printed large‐area focused grid for scatter reduction in cone‐beam CT

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