Combining deterministic and Monte Carlo calculations for fast estimation of scatter intensities in CT

Kyriakou, Yiannis; Riedel, Thomas; Kalender, Willi A.

doi:10.1088/0031-9155/51/18/008

Cited by 123 publications

(110 citation statements)

References 19 publications

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“…So-called data truncation artefacts result, which influence the CT-value accuracy and disturb the diagnostic quality of the images. Correction algorithms [31,32] allow to restore The increased collimation in the z-direction results in increased scatter fractions [33][34][35]. This will induce severe cupping artefacts, i.e.…”

Section: Dose Considerationsmentioning

confidence: 99%

Flat-detector computed tomography (FD-CT)

2007

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Flat-panel detectors or, synonymously, flat detectors (FDs) have been developed for use in radiography and fluoroscopy with the defined goal to replace standard X-ray film, filmscreen combinations and image intensifiers by an advanced sensor system. FD technology in comparison to X-ray film and image intensifiers offers higher dynamic range, dose reduction, fast digital readout and the possibility for dynamic acquisitions of image series, yet keeping to a compact design. It appeared logical to employ FD designs also for computed tomography (CT) imaging. Respective efforts date back a few years only, but FD-CT has meanwhile become widely accepted for interventional and intraoperative imaging using C-arm systems. FD-CT provides a very efficient way of combining two-dimensional (2D) radiographic or fluoroscopic and 3D CT imaging. In addition, FD technology made its way into a number of dedicated CT scanner developments, such as scanners for the maxillo-facial region or for micro-CT applications. This review focuses on technical and performance issues of FD technology and its full range of applications for CT imaging. A comparison with standard clinical CT is of primary interest. It reveals that FD-CT provides higher spatial resolution, but encompasses a number of disadvantages, such as lower dose efficiency, smaller field of view and lower temporal resolution. FD-CT is not aimed at challenging standard clinical CT as regards to the typical diagnostic examinations; but it has already proven unique for a number of dedicated CT applications, offering distinct practical advantages, above all the availability of immediate CT imaging in the interventional suite or the operating room.

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Section: Dose Considerationsmentioning

confidence: 99%

Flat-detector computed tomography (FD-CT)

2007

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“…[34][35][36][37][38] Further acceleration can potentially be obtained by modeling 1st-order scatter (singlescatter events) using an analytical model and employing a coarse MC simulation to estimate a smooth background of higher-order scatter. 39 Finally, MC simulation can be significantly accelerated by implementation on graphics processing units (GPUs) that provide a fast, parallel computing architecture with standard desktop workstations. The work reported below was performed using a GPU-accelerated MC implementation based on publicly available software library (MC-GPU) recently reported to offer a 27-fold speedup in simulation time over a single CPU.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo study of the effects of system geometry and antiscatter grids on cone‐beam CT scatter distributions

et al. 2013

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Purpose:The proliferation of cone-beam CT (CBCT) has created interest in performance optimization, with x-ray scatter identified among the main limitations to image quality. CBCT often contends with elevated scatter, but the wide variety of imaging geometry in different CBCT configurations suggests that not all configurations are affected to the same extent. Graphics processing unit (GPU) accelerated Monte Carlo (MC) simulations are employed over a range of imaging geometries to elucidate the factors governing scatter characteristics, efficacy of antiscatter grids, guide system design, and augment development of scatter correction. Methods: A MC x-ray simulator implemented on GPU was accelerated by inclusion of variance reduction techniques (interaction splitting, forced scattering, and forced detection) and extended to include x-ray spectra and analytical models of antiscatter grids and flat-panel detectors. The simulator was applied to small animal (SA), musculoskeletal (MSK) extremity, otolaryngology (Head), breast, interventional C-arm, and on-board (kilovoltage) linear accelerator (Linac) imaging, with an axis-todetector distance (ADD) of 5, 12, 22, 32, 60, and 50 cm, respectively. Each configuration was modeled with and without an antiscatter grid and with (i) an elliptical cylinder varying 70-280 mm in major axis; and (ii) digital murine and anthropomorphic models. The effects of scatter were evaluated in terms of the angular distribution of scatter incident upon the detector, scatter-to-primary ratio (SPR), artifact magnitude, contrast, contrast-to-noise ratio (CNR), and visual assessment. Results: Variance reduction yielded improvements in MC simulation efficiency ranging from ∼17-fold (for SA CBCT) to ∼35-fold (for Head and C-arm), with the most significant acceleration due to interaction splitting (∼6 to ∼10-fold increase in efficiency). The benefit of a more extended geometry was evident by virtue of a larger air gap-e.g., for a 16 cm diameter object, the SPR reduced from 1.5 for ADD = 12 cm (MSK geometry) to 1.1 for ADD = 22 cm (Head) and to 0.5 for ADD = 60 cm (C-arm). Grid efficiency was higher for configurations with shorter air gap due to a broader angular distribution of scattered photons-e.g., scatter rejection factor ∼0.8 for MSK geometry versus ∼0.65 for C-arm. Grids reduced cupping for all configurations but had limited improvement on scatterinduced streaks and resulted in a loss of CNR for the SA, Breast, and C-arm. Relative contribution of forward-directed scatter increased with a grid (e.g., Rayleigh scatter fraction increasing from ∼0.15 without a grid to ∼0.25 with a grid for the MSK configuration), resulting in scatter distributions with greater spatial variation (the form of which depended on grid orientation). Conclusions: A fast MC simulator combining GPU acceleration with variance reduction provided a systematic examination of a range of CBCT configurations in relation to scatter, highlighting the magnitude and spatial uniformity of individual scatter components, illustrating trad...

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“…MC simulations are more accurate and general ͑a 6%-10% RMS agreement with measurements reported for a CBCT geometry 17 ͒, however, they are computationally demanding, posing an unfavorable trade-off between accuracy and speed. Hybrid deterministic-stochastic techniques 18,19 show promise of resolving this dilemma.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo evaluation of scatter mitigation strategies in cone‐beam CT

Lazos

Williamson

2010

Medical Physics

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Purpose: To investigate the efficacy of two widely used scatter mitigation methods: antiscatter grids ͑ASGs͒ and beam modulating with bowtie filters ͑BTFs͒, in combination with subtractive scatter correction or zeroth order normalization phantom calibration, for improving image noise, contrast, contrast-to-noise ratio ͑CNR͒, and image uniformity for on-board cone-beam CT ͑CBCT͒ imaging systems used for image-guided radiation therapy. Methods: PTRAN Monte Carlo CBCT x-ray projections of head and pelvic phantoms were calculated for combinations of beam-modulation and scatter rejection methods and images were reconstructed by in-house developed software. In addition, a simple one-dimensional analytic model was developed to predict scatter-to-primary ratio ͑SPR͒ and CNR as a function of cylindrical phantom thickness, ASG transmission, and beam modulation with bow-tie filters. Results: ASGs were found to have slightly negative or no effect on head phantom image CNR and to modestly improve CNR ͑10%-20%͒ in pelvic phantom images. However, scatter subtraction and norm-phantom calibration perform better when applied on data acquired with ASGs. Scatter subtraction improves CT number accuracy, but increases noise, and in high SPR/low primary-photon transmission scenarios can dramatically reduce CNR and introduce streaking artifacts. The BTF is found to reduce SPR and image noise, resulting in a better trade-off between CNR and imaging dose, but introduces a circular band artifact. Conclusions: Our study shows that ASGs have a modest positive impact in pelvic scans and negative in head scans, scatter subtraction improves the HU accuracy but reduces CNR, while BTF has a clearly positive effect.

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Combining deterministic and Monte Carlo calculations for fast estimation of scatter intensities in CT

Cited by 123 publications

References 19 publications

Flat-detector computed tomography (FD-CT)

Flat-detector computed tomography (FD-CT)

Monte Carlo study of the effects of system geometry and antiscatter grids on cone‐beam CT scatter distributions

Monte Carlo evaluation of scatter mitigation strategies in cone‐beam CT

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