Anti-scatter Grid Research Articles

Tube voltage in chest and abdomen DR imaging: Which settings return maximal non-prewhitening model observer with eye filter (NPWE) detectability?

The non-prewhitening computational model observer with eye filter (NPWE) has been shown to reasonably predict human observer performance in general radiography and is an appropriate substitute when real clinical trials are not feasible. In this study, the NPWE model observer is used to detect specific tasks (circular designer nodules) ranging between 1 and 30mm in diameter using chest and abdomen phantom images acquired across the diagnostic energy range (60-125 kVp) with and without an anti-scatter grid. The aim of this study was to derive tube voltage (kVp) settings that return maximal NPWE detectability (d') of designer nodules, for digital radiography (DR) chest and abdomen imaging. Images of a chest phantom (LucAl phantom) and a surrogate for an abdomen (18.5cm PMMA) were acquired across the diagnostic energy range (60-125 kVp) with matched effective dose (for the respective anatomies), with and without an anti-scatter grid, on a general x-ray system. Images were captured using an Agfa DX-D 40C wireless indirect caesium iodide (CsI) imaging panel. Modulation transfer function (MTF), normalized noise power spectrum (NNPS), and contrast (C) were measured in each image and the detectability index d' was calculated for circular designer nodules with diameters ranging from 1 to 30mm (in steps of 1mm). The calculated d' peaked at a nodule diameter of 3mm irrespective of tube voltage, for both chest and abdomen images. A tube voltage of 80kVp returned maximal d' for chest imaging across all nodule diameters both with and without an anti-scatter grid. A tube voltage of 70 kVp returned maximal d' for abdomen imaging. The NPWE observer model has been used to derive tube voltages (kVp) that return maximal detectability (d') of designer nodules for chest and abdomen radiography using a modern DR imaging system. This will provide the medical physicist with a starting point in the task of optimising tube voltage range for chest and abdomen imaging.

A virtual anti-scatter grid for multi-energy photon counting detector systems

Photon-counting (PC) systems are the next technological generation of medical computed tomography (CT) imaging and is being worked on by all major system providers. CT devices that are based on PC detectors enable multi-energy data collection. The information-content of this data can be used to obtain more detailed patient data, which improves the quality of reconstructions, compared to conventional detector systems. However, PC CT systems are subject to radiation scatter as just as any other imaging systems is. Conventionally anti-scatter grids (ASG) are used to reduce the scatter effect. These are however an imperfect solution, especially for PC detectors. In this work, a software-based scatter correction method, thus a virtual ASG is proposed. The method is tailoring a new statistical model in the measurement space and combining it with the statistical inversion method called Markov chain Monte Carlo (MCMC). The method can recover the measurement data from dense projections. We present the method on simulated data of a single photon emission computed tomography (SPECT) problem for which only under-sampled data is available. However, our approach can in principle be generalised to CT, PC-CT, Positron emission tomography (PET), radiotherapy, or even digital radiography problems. The results show that the proposed model performs similarly as physical ASGs and for cases where ASGs are not possible. The model further offers a significant improvement in the quality of the reconstruction image compared to the image reconstruction from original under-sampled data.

1071: Prospective trial on CBCT imaging with 2D antiscatter grid: initial experience with image quality

1071: Prospective trial on CBCT imaging with 2D antiscatter grid: initial experience with image quality

Scatter estimation and correction using time-of-flight and deconvolution in x-ray medical imaging.

Objective Time-of-flight (TOF) scatter rejection requires a total timing jitter,
including the detector timing jitter and the X-ray source's pulses width, of 50 ps or less
to mitigate most of the effects of scattered photons in radiography and CT imaging.
However, since the total contribution of the source and detector to the timing jitter
can be retrieved during an acquisition with nothing between the source and detector,
it can be demonstrated that this contribution may be partially removed to improve
the image quality.
Approach A scatter correction method using iterative deconvolution of the measured
time point-spread function estimates the number of scattered photons detected in each
pixel. To evaluate the quality of the estimation, GATE was used to simulate the
radiography of a water cylinder with bone inserts, and a head and torso in a system
with total timing jitters from 100 ps up to 500 ps full-width-at-half-maximum.
Main results With a total timing jitter of 200 ps, 89% of the contrast degradation
caused by scattered photons was recovered in a head and torso radiography, compared
to 28% with a simple time threshold method. Corrected images using the estimation
have a percent root-mean square error between 2 and 14% in both phantoms with
timing jitters from 100 to 500 ps which is lower than the error achieved with scatter
rejection alone at 100 ps.
Significance TOF X-ray imaging has the potential to mitigate the effects of the
scattering contribution and offers an alternative to anti-scatter grids that avoids loss
of primary photons. Compare to simple TOF scatter rejection using only a threshold,
the deconvolution estimation approach has lower requirements on both the source and
detector. These requirements are now within reach of state-of-the-art systems.

Correction of scatter in CBCT with a new grid design

Objective. This study aims at developing a simple and rapid Compton scatter correction approach for cone-beam CT (CBCT) imaging. Approach. In this work, a new Compton scatter estimation model is established based on two distinct CBCT scans: one measures the full primary and scatter signals without anti-scatter grid (ASG), and the other measures a portion of primary and scatter signals with ASG. To accelerate the entire data acquisition speed, a half anti-scatter grid (h-ASG) that covers half of the full detector surface is proposed. As a result, the distribution of scattered x-ray photons could be estimated from a single CBCT scan. Physical phantom experiments are conducted to validate the performance of the newly proposed scatter correction approach. Main results. Results demonstrate that the proposed half grid approach can quickly and precisely estimate the distribution of scattered x-ray photons from only one single CBCT scan, resulting in a significant reduction of shading artifacts. In addition, it is found that the h-ASG approach is less sensitive to the grid transmission fractions, grid ratio and object size, indicating a robust performance of the new method. Significance. In the future, the Compton scatter artifacts can be quickly corrected using a half grid in CBCT imaging.

Local color display technology

AbstractThe local color display technology utilizes a high refresh rate LCD open‐cell without a color filter and enables color adjustment through independent RGB backlight zones isolated by an anti‐scatter grid (ASG). Synchronized calibration between the open‐cell and the backlight zones is achieved by aligning the backlight controller with the vertical clock pulse (CPV)/vertical start pulse (STV) signals in the open‐cell gate driver, thereby determining the open‐cell scan line position. Once synchronous calibration is completed, the backlight controller refreshes the corresponding RGB backlight zones whenever the open‐cell scan line passes through them. The local color display technology can reduce the cost of open‐cell by 20%, improve resolution by three times, enhance brightness by eight times, expand the color gamut to BT2020, and improve grayscale to 32‐bits.

Influence of anatomical structure on antiscatter grid performance in 2D: application to x-ray angiography and a prototype 29:1 ratio grid

Objective. The use of uniform phantoms to assess the influence of x-ray scatter and antiscatter grids on x-ray angiography and fluoroscopy image quality disregards the influence of spatially variable x-ray attenuation of patients. The purpose of this work was to measure scatter to primary ratio (SPR) and antiscatter grid SNR improvement factor (K SNR) using experimental conditions which better mimic patient imaging conditions. Approach. Three adult-sized anthropomorphic phantoms were used. AP and lateral projection images of the thorax and abdomen were acquired with and without an antiscatter grid. Grids with ratio 15:1 and 29:1 (r15, r29) and x-ray fields of view 20, 25 (thorax) and 32, 42 cm (abdomen) were tested. Combined with a-priori measurements of grid scatter and primary transmission fractions, these images were used to calculate 2D SPR and K SNR maps. Main results. Results demonstrated that measurements by uniform phantom do not describe the complex 2D SPR and K SNR distributions associated with anthropomorphic phantoms. The regions of the images with the lowest primary x-ray intensity (greatest attenuation) had the highest SPR and the highest K SNR attributable to the grids. Considering all conditions, the 95th percentile of the SPR maps was in the range 42%–185% greater than the median values and that of the K SNR maps was 4%–20% higher than the median values. The combined influences of SID 120 vs. 107 cm and r29 vs. r15 grid resulted in K SNR in the range 1.05–1.49. Significance. Performance of anti-scatter grids using anatomically complex phantoms highlights the substantial variation of SPR and K SNR within 2D images. Also, this work demonstrates the benefit of the prototype r29 grid for thoracic and abdominal angiography imaging conditions is substantial, especially for large patients and radiodense image regions.

A comprehensive assessment of a prototype high ratio antiscatter grid in interventional cardiology using experimental measurements and Monte Carlo simulations

Objective. To assess the performance of a new antiscatter grid design in interventional cardiology for image quality improvement and dose reduction using experimental measurements and Monte Carlo (MC) simulation. Approach. Experimental measurements were performed on an angiography system, using a multi-layered tissue simulating composite phantom made from of poly(methyl methacrylate), aluminium and expanded polystyrene (2/0.2/0.7 cm). The total phantom thickness ranged from 20.3 cm to 40.6 cm. Four conditions were compared; (A) 105 cm source-image receptor distance (SID) without grid, (B i) 105 cm SID with grid ratio (r) and strip density (N) (r15N80), (B ii) 120 cm SID without grid, and (Biii) 120 cm SID with high ratio grid (r29N80). The system efficiency (η), defined by the signal-to-noise ratio, was compared from the B conditions against case A. These conditions were also simulated with MC techniques, allowing additional phantom compositions to be explored. Weighted image quality improvement factor (ηw (u)) was studied experimentally at a specific spatial frequency due to the SID change. Images were simulated with an anthropomorphic chest phantom for the different conditions, and the system efficiency was compared for the different anatomical regions. Main results. Good agreement was found between the η and ηw (u) methods using both measured and simulated data, with average relative differences between 2%–11%. Case B iii provided higher η values compared to A, and B i for thicknesses larger than 20.3 cm. In addition, case B iii also provided higher η values for high attenuating areas in the anthropomorphic phantom, such as behind the spine. Significance. The new antiscatter grid design provided higher system efficiency compared to the standard grid for the parameters explored in this work.

Impact of scatter radiation on spectral quantification performance of first- and second-generation dual-layer spectral computed tomography.

To assess the impact of scatter radiation on quantitative performance of first and second-generation dual-layer spectral computed tomography (DLCT) systems. A phantom with two iodine inserts (1 and 2mg/mL) configured to intentionally introduce high scattering conditions was scanned with a first- and second-generation DLCT. Collimation widths (maximum of 4cm for first generation and 8cm for second generation) and radiation dose levels were varied. To evaluate the performance of both systems, the mean CT numbers of virtual monoenergetic images (MonoEs) at different energies were calculated and compared to expected values. MonoEs at 50 versus 150keV were plotted to assess material characterization of both DLCTs. Additionally, iodine concentrations were determined, plotted, and compared against expected values. For each experimental scenario, absolute errors were reported. An experimental setup, including a phantom design, was successfully implemented to simulate high scatter radiation imaging conditions. Both CT scanners illustrated high spectral accuracy for small collimation widths (1 and 2cm). With increased collimation (4cm), the second-generation DLCT outperformed the earlier DLCT system. Further, the spectral performance of the second-generation DLCT at an 8cm collimation width was comparable to a 4cm collimation on the first-generation DLCT. A comparison of the absolute errors between both systems at lower energy MonoEs illustrates that, for the same acquisition parameters, the second-generation DLCT generated results with decreased errors. Similarly, the maximum error in iodine quantification was less with second-generation DLCT (0.45 and 0.33mg/mL for the first and second-generation DLCT, respectively). The implementation of a two-dimensional anti-scatter grid in the second-generation DLCT improves the spectral quantification performance. In the clinical routine, this improvement may enable additional clinical benefits, for example, in lung imaging.

Dose Reduction in Medical Radiography: Advancing Veterinary Diagnostic Solutions

In this study, we investigated photon attenuation using an anti-scatter lead grid with a flat panel detector (FPD) and aimed to mitigate it by implementing a linear array detector (LAD). We developed a mechanical system that facilitates X-ray scans using the LAD. For comparison, we selected a standard FPD unit. To assess the differences in entrance skin dose (ESD) between the LAD and FPD systems, we initially utilized anthropomorphic phantoms, followed by water phantoms for exposure tests. Results showed that at a water depth of 10 cm, the ESD from the LAD was 22% lower than that from the FPD. At 30 cm this ratio was increased up to 40%. As water thickness increased, the benefits of using LAD became more evident, demonstrated by a lower ESD. This finding highlights the potential utility of implementing this equipment in veterinary radiography, particularly for imaging animals and their anatomical sites with thicker tissues.

Dose Reduction in Medical Radiography: Advancing Veterinary Diagnostic Solutions

In this study, we investigated photon attenuation using an anti-scatter lead grid with a flat panel detector (FPD) and aimed to mitigate it by implementing a linear array detector (LAD). We developed a mechanical system that facilitates X-ray scans using the LAD. For comparison, we selected a standard FPD unit. To assess the differences in entrance skin dose (ESD) between the LAD and FPD systems, we initially utilized anthropomorphic phantoms, followed by water phantoms for exposure tests. Results showed that at a water depth of 10 cm, the ESD from the LAD was 22% lower than that from the FPD. At 30 cm this ratio was increased up to 40%. As water thickness increased, the benefits of using LAD became more evident, demonstrated by a lower ESD. This finding highlights the potential utility of implementing this equipment in veterinary radiography, particularly for imaging animals and their anatomical sites with thicker tissues.

Radiation Reduction in Paediatric Cardiac Catheterization: We Can Go Even Lower

BackgroundRadiation reduction is an integral component in the management of a paediatric cardiac catheterization laboratory. Simple and easily implementable protocol changes and technical upgrades have been shown to significantly reduce radiation exposure. MethodsRadiation exposures (2020-2022) at Safra Children’s Hospital, Sheba Medical Center, Israel (unit A: n = 672) were retrospectively reviewed, including dose area product (DAP) (μGy m2), DAP/kg, Air Kerma (mGy), and fluoroscopy time (minutes) for 16 procedural types. Median doses were compared with those measured (2011-2014) at the Hospital for Sick Children, Toronto, Canada (unit B: n = 2033). Radiation reduction techniques included fluoroscopy acquisition at 7.5 frames/s, removal of antiscatter grids for children <30 kg, limiting field of view, use of Philips ClarityIQ technology, and an institutional culture of radiation mindedness. ResultsExposure was significantly lower in unit A in 14 of 16 procedure types. Total median doses were lower in unit A (DAP: 91.4 [44.7-205.4] vs 387 [138.2-1339] μGy m2 [P < 0.001], DAP/kg: 9.33 [4.3-16.4] vs 29.22 [12.8-65.9] μGy m2/kg [P < 0.001], and Air Kerma: 14.9 [7.8-29] vs 61 [23-176.4] mGy [P < 0.001]) despite higher fluoroscopy time (14.1 [4.2-24.6] vs 12.3 [6.8-23.3] minutes [P = 0.03]). DAP was lower for specific procedures including pulmonary valvuloplasty (46.3 [14.3-219.3] vs 127 [60-323] μGy m2 [P < 0.001]) and patent ductus arteriosus closure (51.9 [18.8-111.8] vs 178 [96-410] μGy m2 [P < 0.001]). ConclusionsEnhanced radiation reduction techniques can lead to lower than previously published exposure levels across a wide range of procedure types when employing dose-limiting protocols and radiation reduction technology.

Dose Reduction in Medical Radiography: Advancing Veterinary Diagnostic Solutions

In this study, we investigated photon attenuation using an anti-scatter lead grid with a flat panel detector (FPD) and aimed to mitigate it by implementing a linear array detector (LAD). We developed a mechanical system that facilitates X-ray scans using the LAD. For comparison, we selected a standard FPD unit. To assess the differences in entrance skin dose (ESD) between the LAD and FPD systems, we initially utilized anthropomorphic phantoms, followed by water phantoms for exposure tests. Results showed that at a water depth of 10 cm, the ESD from the LAD was 22% lower than that from the FPD. At 30 cm this ratio was increased up to 40%. As water thickness increased, the benefits of using LAD became more evident, demonstrated by a lower ESD. This finding highlights the potential utility of implementing this equipment in veterinary radiography, particularly for imaging animals and their anatomical sites with thicker tissues.

The Influence of Anti-scatter Grid Usage for Knee Computerized Radiography

Aims: This experimental study investigated the effect of using an anti-scatter grid in computerized knee radiography (CR) on image quality (IQ) and patient surface radiation dose (Equivalent Surface Air Kerma – Ka,e), measured with an ionization chamber. Place and Duration of Study: The experimental study was conducted between February 2024 and April 2024, in the radiodiagnosis laboratory belonging to the Medical Physics and Radiology Technology courses at the Franciscan University (UFN) in the city of Santa Maria, Rio Grande do Sul. Methodology: Utilizing a semi-anatomical knee phantom to simulate clinical examination conditions, ten images were acquired, with five obtained using technique 1 (70 kV, 200mA, and 20mAs) and another five with technique 2 (70 kVp, 200mA, and 5 mAs), with and without an anti-scatter grid, respectively. The phantom images were digitized in a CR system and quantified using a publicly available automatic analyzer software based on histograms and regions of interest (ROI), defined by signal and noise. The obtained results were used to calculate the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and radiographic contrast (RC), considered IQ descriptors. Results: As a selection criterion, the percentage deviation (D%) was chosen, considering technique 1 as the reference concerning technique 2. It was observed that technique 1 showed an SNR 1.20%, RC 3.86%, and Ka,e 73.68% higher than technique 2; on the other hand, technique 2 indicated a CNR 4.76% higher compared to technique 1. Conclusion: It is concluded that technique 2 without an anti-scatter grid may be preferable when considering the principle of optimization, where the dose is significantly reduced without a significant loss in IQ descriptors.

A deep-learning-based scatter correction with water equivalent path length map for digital radiography.

We proposed a new deep learning (DL) model for accurate scatter correction in digital radiography. The proposed network featured a pixel-wise water equivalent path length (WEPL) map of subjects with diverse sizes and 3D inner structures. The proposed U-Net model comprises two concatenated modules: one for generating a WEPL map and the other for predicting scatter using the WEPL map as auxiliary information. First, 3D CT images were used as numerical phantoms for training and validation, generating observed and scattered images by Monte Carlo simulation, and WEPL maps using Siddon's algorithm. Then, we optimised the model without overfitting. Next, we validated the proposed model's performance by comparing it with other DL models. The proposed model obtained scatter-corrected images with a peak signal-to-noise ratio of 44.24 ± 2.89dB and a structural similarity index measure of 0.9987 ± 0.0004, which were higher than other DL models. Finally, scatter fractions (SFs) were compared with other DL models using an actual phantom to confirm practicality. Among DL models, the proposed model showed the smallest deviation from measured SF values. Furthermore, using an actual radiograph containing an acrylic object, the contrast-to-noise ratio (CNR) of the proposed model and the anti-scatter grid were compared. The CNR of the images corrected using the proposed model are 16% and 82% higher than those of the raw and grid-applied images, respectively. The advantage of the proposed method is that no actual radiography system is required for collecting training dataset, as the dataset is created from CT images using Monte Carlo simulation.

Computational evaluation of the bucky components influence on the estimation of normalized glandular dose in digital mammography

The mean glandular dose (MGD) is the most suitable dosimetric quantity used in mammography to describe the absorbed dose by the breast, although it cannot be directly acquired. Studies have provided conversion factors widely implemented in international dosimetry protocols to estimate MGD, such as normalized glandular dose (DgN). Over time, the DgN estimation was refined by considering geometric models that approach a real clinical environment, such as new anode/filter combinations, compression plate and breast models. However, there is no detailed study of how the bucky (support plate, antiscatter grid and detector) can affect the DgN estimation. A modified PENELOPE Monte Carlo code was used for DgN estimation. The irradiation geometric model was built as a complete digital mammography system, considering a homogeneous breast and different typical bucky models in commercial mammography units. Simulations were carried out for mono and polyenergetic beams considering different imaging geometries. Studies with monoenergetic beams showed that the bucky presence affected DgN mainly for higher beam energies and thinner breasts. The breast support plate was the bucky component that most affected the DgN, followed by the antis-scatter grid and finally, the image detector. Studies with polyenergetic conventional (low-energy) spectra showed that the bucky exerted a minimal influence on DgN values (less than 1.0%). For high-energy spectra, mainly employed in modalities such as contrast-enhanced digital mammography, the DgN values were more affected by the bucky, increasing by 4.8% the DgN values for a 2 cm thick breast and a W/Cu 50 kV spectrum. Bucky inclusion in computer simulations is highly recommended mainly for thinner breasts and high-energy spectra. To simplify the simulations, we confirm that a homogeneous carbon fibre block support, with thickness between 3.9 and 4.1 mm, can be used as a good substitute for a complete bucky model.

Effect of scatter suppression with 2D antiscatter grids in photon counting compact CBCT.

Energy sensitive and photon counting detectors can provide improved tissue visualization and material quantification capabilities in Cone Beam Computed Tomography (CBCT) systems. However, their implementation in CBCT systems is more challenging, which is in part due to high fluence of scattered X-rays in wide cone angle CBCT geometry. Specifically, high scatter contamination in lower energy spectrum challenges reconstruction of high fidelity CBCT images by using lower energy X-rays. To address this problem, we investigated a robust scatter rejection with 2D antiscatter grids in a benchtop photon counting and compact CBCT system. The benchtop system employs a 35 cm wide CdTe photon counting detector with two energy thresholds. To reject scatter, a dedicated 2D antiscatter grid (2D grid) prototype made from tungsten was developed and mounted directly on the detector. To correct residual scatter not stopped by the 2D grid, a measurement-based scatter correction method, referred to as Grid-based Scatter Sampling (GSS), was utilized. Without 2D grid, scatter to primary ratio (SPR) reached 2.3 in the 15-40 keV energy bin. SPR was factor of 3 higher in the lowest energy bin when compared to the highest energy bin (90-120 keV). With the 2D grid, SPR was reduced below 0.14, and SPR values were more homogenous across the energy spectrum. CT number nonuniformity was factor of 3 lower in both low and high energy bin CBCT reconstructions. Improvement in contrast to noise ratio and contrast was more pronounced in the low energy bin CBCT images. This work indicates that 2D grids can significantly reduce spectral contamination caused by scatter in photon counting compact CBCT, and potentially enable higher fidelity CBCT image reconstructions.

Geant4 Simulation of Scatter Radiation Removal: Comparison and Validation of Anti-scatter Grid and Air Gap for X-ray Mammography

Abstract: X-ray mammography modality provides excellent low-contrast resolution images with low scatter radiation, making it the gold standard in diagnosing breast cancer. Anti-scatter grid and air gap techniques are typically used to further minimize the scatter radiation and improve image quality. Thus, Geant4 simulation was used to investigate the effectiveness of these techniques in removing scatter radiation in X-ray mammography. The effectiveness of an anti-scatter grid was evaluated using the Bucky factor, where it linearly increased with increasing the anti-scatter grid ratio. It was found that increasing the grid frequency affects the Bucky factor depending on the design of the grid ratio. This research proved that designing an anti-scatter grid with high grid frequency (80 lp/mm), low grid ratio (2:1), and proper orientation minimized common anti-scatter grid artifacts. The effectiveness of the air gap technique was also evaluated using the air gap dose factor. It increased non-linearly with increasing magnification. This research validated that using smaller pixel sizes and small focal spot sizes improved spatial resolution with magnification. Our simulation validated that the anti-scatter grid and air gap were effective techniques in removing scatter radiation. By comparing these techniques, the anti-scatter grid was more effective in removing scatter radiation at the expense of increasing the radiation absorbed dose with the exception of 2.0 magnification. It’s recommended to be extremely cautious when using 2.0 magnification or a grid ratio higher or equal to 8:1. These parameters may cause the radiation absorbed dose to be increased by several folds. Keywords: Geant4, Gate, X-ray mammography, Scatter removal, Anti-scatter grid, Air gap.

A combined analytical and Monte Carlo method for detailed simulations of antiscatter grids in x-ray medical imaging: implementing scatter within the grid

Objective. To implement a hybrid method, which combines analytical tracking and interaction simulation using Monte Carlo (MC) techniques, in order to model photon transport inside antiscatter grids (ASG) for x-ray imaging. Approach. A new tally was developed for PENELOPE (v.2018) and penEasy (v. 2020) MC code to simulate photon transmission through ASGs. Two established analytical algorithms from the literature were implemented in this tally. In addition, a new hybrid method was introduced by extending one of the analytical algorithms to include photon-interactions inside the grid, while preserving the imaged grid structure. Calculations of primary (TP), scatter (TS), and total (TT) grid transmissions in addition to the Q factor (Q = TP2/TT ) were performed. The new tally was validated for a quadric geometry ASG, and experimental measurements with a PMMA phantom of several thicknesses. In addition, the contribution of the scatter inside the grid was studied for three interspace materials, and a high resolution image of the grid was simulated. Main results. An excellent agreement was found between the two analytical models compared with the quadric grid without scatter, and the hybrid method with the geometrical grid with scatter. Average deviations of 0.2% and 1.4% were found between TP and TS for the hybrid method and quadric grid, while for the hybrid method and experimental measurements these values were 1% and 20%. Antiscatter grids with aluminium as interspace material had the highest amount of scatter from inside the grid to the final image, followed up by paper fibre and air. The high resolution image of the grid was equivalent using the quadric geometry or the hybrid mode. Significance. The hybrid method provides a means of studying scattered radiation from the antiscatter grid with the advantage of higher performance, with results that are consistent with a full quadric geometry simulation of the ASG.

An analytical form of ring artifact correction for computed tomography based on directional gradient domain optimization.

Ring artifact is a common problem in Computed Tomography (CT), which can lead to inaccurate diagnoses and treatment plans. It can be caused by various factors such as detector imperfections, anti-scatter grids, or other nonuniform filters placed in the x-ray beam. Physics-based corrections for these x-ray source and detector non-uniformity, in general cannot completely get rid of the ring artifacts. Therefore, there is a need for a robust method that can effectively remove ring artifacts in the image domain while preservingdetails. This study aims to develop an effective method for removing ring artifacts from reconstructed CTimages. The proposed method starts by converting the reconstructed CT image containing ring artifacts into polar coordinates, thereby transforming these artifacts into stripes. Relative Total Variation is used to extract the image's overall structural information. For the efficient restoration of intricate details, we introduce Directional Gradient Domain Optimization (DGDO) and design objective functions that make use of both the image's gradient and its overall structure. Subsequently, we present an efficient analytical algorithm to minimize these objective functions. The image obtained through DGDO is then transformed back into Cartesian coordinates, finalizing the ring artifact correctionprocess. Through a series of synthetic and real-world experiments, we have effectively demonstrated the prowess of our proposed method in the correction of ring artifacts while preserving intricate details in reconstructed CT images. In a direct comparison, our method has exhibited superior visual quality compared to several previous approaches. These results underscore the remarkable potential of our approach for enhancing the overall quality and clinical utility of CTimaging. The proposed method offers an analytical solution for removing ring artifacts from CT images while preserving details. As ring artifacts are a common problem in CT imaging, this method has high practical value in the medical field. The proposed method can improve image quality and reduce the difficulty of disease diagnosis, thereby contributing to better patientcare.