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

Park, Yeonok; Alexeev, Timur; Miller, Brian W.; Miften, Moyed; Altunbas, Cem

doi:10.1002/mp.14756

Cited by 13 publications

(30 citation statements)

References 39 publications

(130 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, the extension to covering a large area of the x‐ray detector is not straightforward due to design, fabrication, and implementation considerations 67 . 2D‐ASGs have been previously manufactured in tungsten, due to its higher attenuation coefficient 24,35,36 . However, our results show that large‐area 2D‐ASGs manufactured in cobalt–chromium alloy are able to significantly improve image quality for high‐scatter scenarios at relatively low diagnostic energies (i.e., 80 kVp).…”

Section: Discussionmentioning

confidence: 86%

“…These residual stresses compound as the part occupies a larger area of the build plate. To the best of our knowledge, the largest 2D‐ASG prototypes described in the literature have not exceeded an area of 3 × 20 cm 2 of the build plate 24,33,35–37,67 . Additionally, the assembling of multiple prototypes into a larger grid presents challenges such as alignment of the assembly and thicker septa at the interface.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2022

View full text Add to dashboard Cite

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

show abstract

Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

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

et al. 2022

View full text Add to dashboard Cite

show abstract

“…Because the acquisition of CBCT scans utilizes a large-area detector, deterioration in CBCT image quality due to beam scattering is inevitable. However, although this study included improvement in low-dose CBCT image quality via the proposed method, measurement-based scatter correction such as an anti-scatter grid ( 45 ) or beam blocker ( 19 , 46 ) was not applied to the acquired CBCT projection data. Considering that scatter correction methods can be used to acquire CBCT projection data, further reductions in the SNU of low-dose CBCT image quality can be expected.…”

Section: Discussionmentioning

confidence: 99%

Mutual Information-Based Non-Local Total Variation Denoiser for Low-Dose Cone-Beam Computed Tomography

et al. 2021

View full text Add to dashboard Cite

Conventional non-local total variation (NLTV) approaches use the weight of a non-local means (NLM) filter, which degrades performance in low-dose cone-beam computed tomography (CBCT) images generated with a low milliampere-seconds (mAs) parameter value because a local patch used to determine the pixel weights comprises noisy-damaged pixels that reduce the similarity between corresponding patches. In this paper, we propose a novel type of NLTV based on a combination of mutual information (MI): MI-NLTV. It is based on a statistical measure for a similarity calculation between the corresponding bins of non-local patches vs. a reference patch. The weight is determined in terms of a statistical measure comprising the MI value between corresponding non-local patches and the reference-patch entropy. The MI-NLTV denoising process is applied to CBCT images generated by the analytical reconstruction algorithm using a ray-driven backprojector (RDB). The MI-NLTV objective function is minimized based on the steepest gradient descent optimization to augment the difference between a real structure and noise, cleaning noisy pixels without significant loss of the fine structure and details that remain in the reconstructed images. The proposed method was evaluated using patient data and actual phantom measurement data acquired with lower mAs. The results show that integrating the RDB further enhances the MI-NLTV denoising-based analytical reconstruction algorithm to achieve a higher CBCT image quality when compared with those generated by NLTV denoising-based approach, with an average of 15.97% higher contrast-to-noise ratio, 2.67% lower root mean square error, 0.12% lower spatial non-uniformity, 1.14% higher correlation, and an average of 18.11% higher detectability index. These quantitative results indicate that the incorporation of MI makes the NLTV more stable and robust than the conventional NLM filter for low-dose CBCT imaging. In addition, achieving clinically acceptable CBCT image quality despite low-mAs projection acquisition can reduce the burden on common online CBCT imaging, improving patient safety throughout the course of radiotherapy.

show abstract

“…4 Physics-based methods suppress scatter by adding additional hardware to the system, such as anti-scatter grids. [5][6][7] They can prevent or decrease scattered Xrays reaching the detector and therefore reduce the scatter-to-primary ratio (SPR). However, these methods will increase the radiation dose to patients to compensate for the loss of signal-to-noise ratio caused by the absorption of primary photons.…”

Section: Introductionmentioning

confidence: 99%

“…Over the years, many studies have aimed to address the CBCT scatter problem, which can be broadly categorized into physics‐based and algorithm‐based methods 4 . Physics‐based methods suppress scatter by adding additional hardware to the system, such as anti‐scatter grids 5–7 . They can prevent or decrease scattered X‐rays reaching the detector and therefore reduce the scatter‐to‐primary ratio (SPR).…”

Section: Introductionmentioning

confidence: 99%

A correlated sampling‐based Monte Carlo simulation for fast CBCT iterative scatter correction

Qin¹,

Lin²,

Li³

et al. 2022

Medical Physics

View full text Add to dashboard Cite

Background: In recent years, cone-beam computed tomography (CBCT) has played an important role in medical imaging. However, the applications of CBCT are limited due to the severe scatter contamination. Conventional Monte Carlo (MC) simulation can provide accurate scatter estimation for scatter correction, but the expensive computational cost has always been the bottleneck of MC method in clinical application. Purpose: In this work, an MC simulation method combined with a variance reduction technique called correlated sampling is proposed for fast iterative scatter correction. Methods: Correlated sampling exploits correlation between similar simulation systems to reduce the variance of interest quantities. Specifically, conventional MC simulation is first performed on the scatter-contaminated CBCT to generate the initial scatter signal. In the subsequent correction iterations, scatter estimation is then updated by applying correlated MC sampling to the latest corrected CBCT images by reusing the random number sequences of the task-related photons in conventional MC. Afterward, the corrected projections obtained by subtracting the scatter estimation from raw projections are utilized for FDK reconstruction. These steps are repeated until an adequate scatter correction is obtained. The performance of the proposed framework is evaluated by the accuracy of the scatter estimation, the quality of corrected CBCT images and efficiency. Results: Overall, the difference in mean absolute percentage error between scatter estimation with and without correlated sampling is 0.25% for full-fan case and 0.34% for half -fan case, respectively. In simulation studies, scatter artifacts are substantially eliminated, where the mean absolute error value is reduced from 15 to 2 HU in full-fan case and from 53 to 13 HU in half -fan case. Scatterto-primary ratio is reduced to 0.02 for full-fan and 0.04 for half -fan, respectively. In phantom study, the contrast-to-noise ratio (CNR) is increased by a factor of 1.63, and the contrast is increased by a factor of 1.77. As for clinical studies, the CNR is improved by 11% and 14% for half -fan and full-fan, respectively. The contrast after correction is increased by 19% for half -fan and 44% for fullfan. Furthermore, root mean square error is also effectively reduced, especially from 78 to 4 HU for full-fan. Experimental results demonstrate that the figure of merit is improved between 23 and 43 folds when using correlated sampling. The proposed method takes less than 25 s for the whole iterative scatter correction process. Conclusions:The proposed correlated sampling-based MC simulation method can achieve fast and accurate scatter correction for CBCT, making it suitable for real-time clinical use.

show abstract

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

Cited by 13 publications

References 39 publications

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

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

Mutual Information-Based Non-Local Total Variation Denoiser for Low-Dose Cone-Beam Computed Tomography

A correlated sampling‐based Monte Carlo simulation for fast CBCT iterative scatter correction

Contact Info

Product

Resources

About