Model based scatter correction for cone-beam computed tomography

Wiegert, Jens; Bertram, Matthias; Rose, Georg; Aach, Til

doi:10.1117/12.594520

Cited by 39 publications

(31 citation statements)

References 7 publications

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“…This is an important rationale for scatter correction schemes based on computation of the single scatter background, such as proposed in Ref. 12 .…”

Section: Spatial and Angular Dynamic Of Scatter Projectionsmentioning

confidence: 99%

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Scattered radiation in flat-detector based cone-beam CT: analysis of voxelized patient simulations

Wiegert

Bertram

2006

SPIE Proceedings

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This paper presents a systematic assessment of scattered radiation in flat-detector based cone-beam CT. The analysis is based on simulated scatter projections of voxelized CT images of different body regions allowing to accurately quantify scattered radiation of realistic and clinically relevant patient geometries. Using analytically computed primary projection data of high spatial resolution in combination with Monte-Carlo simulated scattered radiation, practically noise-free reference data sets are computed with and without inclusion of scatter. The impact of scatter is studied both in the projection data and in the reconstructed volume for the head, thorax, and pelvis regions. Currently available anti-scatter grid geometries do not sufficiently compensate scatter induced cupping and streak artifacts, requiring additional software-based scatter correction. The required accuracy of scatter compensation approaches increases with increasing patient size.

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“…This is an important rationale for scatter correction schemes based on computation of the single scatter background, such as proposed in Ref. 12 .…”

Section: Spatial and Angular Dynamic Of Scatter Projectionsmentioning

confidence: 99%

“…Several compensation strategies have been reported for fan-beam CT as well as for true cone-beam CT and are either based on suppressing scatter during the measurement by anti-scatter grids 4,5 or aim at compensating the detected scatter by a-posteriori software based methods [6][7][8][9][10][11][12][13] .…”

Section: Introductionmentioning

confidence: 99%

Scattered radiation in flat-detector based cone-beam CT: analysis of voxelized patient simulations

Wiegert

Bertram

2006

SPIE Proceedings

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“…An even faster alternative to such online scatter calculation is provided by precalculating the scatter values for various possible combinations of model parameters in an offline fashion and by storing the results in a look-up table. Another possibility would be to incorporate a recently developed fast scheme for analytical calculation of single scatter 15 .…”

Section: Principle and Overviewmentioning

confidence: 99%

Scatter correction for cone-beam computed tomography using simulated object models

2006

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Scattered radiation is a major source of artifacts in flat detector based cone-beam computed tomography. In this paper, a novel software-based method for retrospective scatter correction is described and evaluated. The method is based on approximation of the imaged object by a simple geometric model (e.g., a homogeneous water-like ellipsoid) that is estimated from the set of acquired projections. This is achieved by utilizing a numerical optimization procedure to determine the model parameters for which there is maximum correspondence between the measured projections and the projections of the model. Monte-Carlo simulations of this model are used for calculation of scatter estimates for the acquired projections. Finally, using the scatter-corrected projections, tomographic reconstruction is conducted by means of cone-beam filtered back-projection. The correction method is evaluated using simulated and experimentally acquired projection data sets of geometric and physical head phantoms. It is found that the method is able to accurately estimate mean scatter levels in X-ray projections, allowing to significantly reduce scatter-caused artifacts in 3D reconstructed images.

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“…However, a significant amount of scatter often remains, which must be estimated and subtracted from the projection data as part of the reconstruction process in order to produce high-quality images. Most scatter correction methods can be categorized as being based either on estimating scatter using computational models [6][7][8][9][10][11][12][13][14] or measuring scatter in situ. [15][16][17][18][19][20] Methods for measuring scatter in situ include collimator shadowing, 15 beam stop arrays, 16 dual scans, 17,18 and primary beam modulation.…”

Section: Introductionmentioning

confidence: 99%

Correction for patient table‐induced scattered radiation in cone‐beam computed tomography (CBCT)

et al. 2011

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Purpose: In image-guided radiotherapy, an artifact typically seen in axial slices of x-ray cone-beam computed tomography ͑CBCT͒ reconstructions is a dark region or "black hole" situated below the scan isocenter. The authors trace the cause of the artifact to scattered radiation produced by radiotherapy patient tabletops and show it is linked to the use of the offset-detector acquisition mode to enlarge the imaging field-of-view. The authors present a hybrid scatter kernel superposition ͑SKS͒ algorithm to correct for scatter from both the object-of-interest and the tabletop. Methods: Monte Carlo simulations and phantom experiments were first performed to identify the source of the black hole artifact. For correction, a SKS algorithm was developed that uses separate kernels to estimate scatter from the patient tabletop and the object-of-interest. Each projection is divided into two regions, one defined by the shadow cast by the tabletop on the imager and one defined by the unshadowed region. The region not shadowed by the tabletop is processed using the recently developed fast adaptive scatter kernel superposition ͑fASKS͒ method which employs asymmetric kernels that best model scatter transport through bodylike objects. The shadowed region is convolved with a combination of slab-derived symmetric SKS kernels and asymmetric fASKS kernels. The composition of the hybrid kernels is projection-angle-dependent. To test the algorithm, pelvis phantom and in vivo data were acquired using a CBCT test stand, a Varian Acuity simulator, and a Varian On-Board Imager, all of which have similar geometries and components. Artifact intensities and Hounsfield unit ͑HU͒ accuracies in the reconstructions were assessed before and after the correction. Results: The hybrid kernel algorithm provided effective correction and produced substantially better scatter estimates than the symmetric SKS or asymmetric fASKS methods alone. HU nonuniformities in the reconstructed pelvis phantom were reduced from 220 to 50 HU ͑i.e., 22%-5%͒. In the in vivo scans, the black hole artifact was reduced by up to 147 HU, a 73% improvement, and anatomical details in the prostate and rectum areas were made considerably more visible. Conclusions: Radiotherapy tabletops, which are generally flatter and larger than those used for diagnostic CT, can produce significant scatter-related artifacts. The proposed hybrid SKS algorithm accurately estimates scatter from both the object-of-interest and the patient tabletop, and resulting image uniformities and HU accuracies are greatly improved.

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Model based scatter correction for cone-beam computed tomography

Cited by 39 publications

References 7 publications

Scattered radiation in flat-detector based cone-beam CT: analysis of voxelized patient simulations

Scattered radiation in flat-detector based cone-beam CT: analysis of voxelized patient simulations

Scatter correction for cone-beam computed tomography using simulated object models

Correction for patient table‐induced scattered radiation in cone‐beam computed tomography (CBCT)

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