Algorithm for X-ray Scatter, Beam-Hardening, and Beam Profile Correction in Diagnostic (Kilovoltage) and Treatment (Megavoltage) Cone Beam CT

Maltz, Jonathan S.; Gangadharan, B; Bose, Supratik; Hristov, Dimitre; Faddegon, Bruce A.; Paidi, A; Bani‐Hashemi, A

doi:10.1109/tmi.2008.928922

Cited by 77 publications

(69 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Such scatter kernels can be measured or simulated using Monte Carlo (MC) methods. 30,31 Monte Carlo simulation offers a potentially accurate method for scatter estimation, but has been somewhat limited in application due to high computational complexity associated with the large number of photon histories (order ∼10 9 ) needed to produce scatter estimates with an acceptably low level of noise. 32 Encouraging methods for MC acceleration are obtained from so-called variance reduction techniques, known from the general theory of MC simulation in terms of forced detection, mean free path transformations, Woodcock tracking, interaction splitting, and Russian roulette.…”

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

View full text Add to dashboard Cite

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...

show abstract

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

View full text Add to dashboard Cite

show abstract

“…[3][4][5] With more precise treatment monitoring from accurate CBCT images, dose delivery errors can be significantly reduced in each fraction 6,7 and further compensated for in subsequent fractions using adaptive radiation therapy. 8,9 However, the current CBCT imaging has severe shading artifacts mainly due to scatter contamination, [10][11][12][13][14] and its current clinical application is therefore limited to patient setup based on only bony structures. To improve CBCT imaging for quantitative use, we recently proposed a shading correction method using planning CT (pCT) as the prior knowledge.…”

Section: Introductionmentioning

confidence: 99%

Quantitative cone‐beam CT imaging in radiation therapy using planning CT as a prior: First patient studies

2012

View full text Add to dashboard Cite

Purpose: Quantitative cone-beam CT (CBCT) imaging is on increasing demand for high-performance image guided radiation therapy (IGRT). However, the current CBCT has poor image qualities mainly due to scatter contamination. Its current clinical application is therefore limited to patient setup based on only bony structures. To improve CBCT imaging for quantitative use, we recently proposed a correction method using planning CT (pCT) as the prior knowledge. Promising phantom results have been obtained on a tabletop CBCT system, using a correction scheme with rigid registration and without iterations. More challenges arise in clinical implementations of our method, especially because patients have large organ deformation in different scans. In this paper, we propose an improved framework to extend our method from bench to bedside by including several new components. Methods: The basic principle of our correction algorithm is to estimate the primary signals of CBCT projections via forward projection on the pCT image, and then to obtain the low-frequency errors in CBCT raw projections by subtracting the estimated primary signals and low-pass filtering. We improve the algorithm by using deformable registration to minimize the geometry difference between the pCT and the CBCT images. Since the registration performance relies on the accuracy of the CBCT image, we design an optional iterative scheme to update the CBCT image used in the registration. Large correction errors result from the mismatched objects in the pCT and the CBCT scans. Another optional step of gas pocket and couch matching is added into the framework to reduce these effects. Results: The proposed method is evaluated on four prostate patients, of which two cases are presented in detail to investigate the method performance for a large variety of patient geometry in clinical practice. The first patient has small anatomical changes from the planning to the treatment room. Our algorithm works well even without the optional iterations and the gas pocket and couch matching. The image correction on the second patient is more challenging due to the effects of gas pockets and attenuating couch. The improved framework with all new components is used to fully evaluate the correction performance. The enhanced image quality has been evaluated using mean CT number and spatial nonuniformity (SNU) error as well as contrast improvement factor. If the pCT image is considered as the ground truth, on the four patients, the overall mean CT number error is reduced from over 300 HU to below 16 HU in the selected regions of interest (ROIs), and the SNU error is suppressed from over 18% to below 2%. The average soft-tissue contrast is improved by an average factor of 2.6. Conclusions: We further improve our pCT-based CBCT correction algorithm for clinical use. Superior correction performance has been demonstrated on four patient studies. By providing quantitative CBCT images, our approach significantly increases the accuracy of advanced CBCT-based clinical applications for IGRT....

show abstract

“…13 In the current simulation framework, the scatter correction method described by Maltz et al 27 was implemented to estimate the scatter signal. The method described by Maltz et al 27 is iterative. We used five iterations in our implementation.…”

Section: Iib2 Scatter Generation and Correctionmentioning

confidence: 99%

Design of a digital beam attenuation system for computed tomography: Part I. System design and simulation framework

Szczykutowicz

Mistretta

2013

Med. Phys.

View full text Add to dashboard Cite

Purpose: The purpose of this work is to introduce a new device that allows for patient-specific imaging-dose modulation in conventional and cone-beam CT. The device is called a digital beam attenuator (DBA). The DBA modulates an x-ray beam by varying the attenuation of a set of attenuating wedge filters across the fan angle. The ability to modulate the imaging dose across the fan beam represents another stride in the direction of personalized medicine. With the DBA, imaging dose can be tailored for a given patient anatomy, or even tailored to provide signal-to-noise ratio enhancement within a region of interest. This modulation enables decreases in: dose, scatter, detector dynamic range requirements, and noise nonuniformities. In addition to introducing the DBA, the simulation framework used to study the DBA under different configurations is presented. Finally, a detailed study on the choice of the material used to build the DBA is presented. Methods: To change the attenuator thickness, the authors propose to use an overlapping wedge design. In this design, for each wedge pair, one wedge is held stationary and another wedge is moved over the stationary wedge. The composite thickness of the two wedges changes as a function of the amount of overlap between the wedges. To validate the DBA concept and study design changes, a simulation environment was constructed. The environment allows for changes to system geometry, different source spectra, DBA wedge design modifications, and supports both voxelized and analytic phantom models. A study of all the elements from atomic number 1 to 92 were evaluated for use as DBA filter material. The amount of dynamic range and tube loading for each element were calculated for various DBA designs. Tube loading was calculated by comparing the attenuation of the DBA at its minimum attenuation position to a filtered non-DBA acquisition. Results: The design and parametrization of DBA implemented FFMCT has been introduced. A simulation framework was presented with which DBA-FFMCT, bowtie filter CT acquisitions, and unmodulated CT acquisitions can be simulated. The study on wedge filter design concluded that the ideal filter material should have an atomic number in the range of 21-34. Iron was chosen for an experimental relative-tube-loading measurement and showed that DBA-FFMCT scans could be acquired with negligible increases in tube power demands. Conclusions: The basic idea of DBA implemented fluence field modulated CT, a simulation framework to verify the concept, and a filter selection study have been presented. The use of a DBA represents another step toward the ultimate in patient specific CT dose delivery as patient dose can be delivered uniquely as a function of view and fan angle using this device.

show abstract

Algorithm for X-ray Scatter, Beam-Hardening, and Beam Profile Correction in Diagnostic (Kilovoltage) and Treatment (Megavoltage) Cone Beam CT

Cited by 77 publications

References 21 publications

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

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

Quantitative cone‐beam CT imaging in radiation therapy using planning CT as a prior: First patient studies

Design of a digital beam attenuation system for computed tomography: Part I. System design and simulation framework

Contact Info

Product

Resources

About