Electronic Grids for Electrostatic Imaging Systems

Muntz, E. P.; Jacobson, George; Kaegi, Emil M.; Klein, David J.

doi:10.1148/121.1.197

Cited by 11 publications

(8 citation statements)

References 12 publications

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“…16 Muntz et al 63 developed a scatter point-source model to describe the dependence of scatter-toprimary ratio (SPR) on system geometry. The model assumes scatter to originate from a virtual point source located at distance y scat from the object plane (isocenter), typically in the direction of the primary x-ray source.…”

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confidence: 99%

Task-based modeling and optimization of a cone-beam CT scanner for musculoskeletal imaging

et al. 2011

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Purpose: This work applies a cascaded systems model for cone-beam CT imaging performance to the design and optimization of a system for musculoskeletal extremity imaging. The model provides a quantitative guide to the selection of system geometry, source and detector components, acquisition techniques, and reconstruction parameters. Methods: The model is based on cascaded systems analysis of the 3D noise-power spectrum (NPS) and noise-equivalent quanta (NEQ) combined with factors of system geometry (magnification, focal spot size, and scatter-to-primary ratio) and anatomical background clutter. The model was extended to task-based analysis of detectability index (d 0 ) for tasks ranging in contrast and frequency content, and d 0 was computed as a function of system magnification, detector pixel size, focal spot size, kVp, dose, electronic noise, voxel size, and reconstruction filter to examine tradeoffs and optima among such factors in multivariate analysis. The model was tested quantitatively versus the measured NPS and qualitatively in cadaver images as a function of kVp, dose, pixel size, and reconstruction filter under conditions corresponding to the proposed scanner. Results: The analysis quantified trade-offs among factors of spatial resolution, noise, and dose. System magnification (M) was a critical design parameter with strong effect on spatial resolution, dose, and x-ray scatter, and a fairly robust optimum was identified at M $ 1.3 for the imaging tasks considered. The results suggested kVp selection in the range of $65-90 kVp, the lower end (65 kVp) maximizing subject contrast and the upper end maximizing NEQ (90 kVp). The analysis quantified fairly intuitive resultse.g., $0.1-0.2 mm pixel size (and a sharp reconstruction filter) optimal for high-frequency tasks (bone detail) compared to $0.4 mm pixel size (and a smooth reconstruction filter) for low-frequency (soft-tissue) tasks. This result suggests a specific protocol for 1 Â 1 (full-resolution) projection data acquisition followed by full-resolution reconstruction with a sharp filter for high-frequency tasks along with 2 Â 2 binning reconstruction with a smooth filter for low-frequency tasks. The analysis guided selection of specific source and detector components implemented on the proposed scanner. The analysis also quantified the potential benefits and points of diminishing return in focal spot size, reduced electronic noise, finer detector pixels, and low-dose limits of detectability. Theoretical results agreed quantitatively with the measured NPS and qualitatively with evaluation of cadaver images by a musculoskeletal radiologist. Conclusions: A fairly comprehensive model for 3D imaging performance in cone-beam CT combines factors of quantum noise, system geometry, anatomical background, and imaging task. The analysis provided a valuable, quantitative guide to design, optimization, and technique selection for a musculoskeletal extremities imaging system under development.

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confidence: 99%

Task-based modeling and optimization of a cone-beam CT scanner for musculoskeletal imaging

et al. 2011

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“…In order to investigate the limitations of the point-source concept the following analytical function describing a generalized point-source model [15][16][17]…”

Section: Variable Point-source Model For Multiple Scatteringmentioning

confidence: 99%

Analytical scatter kernels for portal imaging at 6 MV

Spies

Bortfeld

2001

Medical Physics

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X-ray photon scatter kernels for 6 MV electronic portal imaging are investigated using an analytical and a semi-analytical model. The models are tested on homogeneous phantoms for a range of uniform circular fields and scatterer-to-detector air gaps relevant for clinical use. It is found that a fully analytical model based on an exact treatment of photons undergoing a single Compton scatter event and an approximate treatment of second and higher order scatter events, assuming a multiple-scatter source at the center of the scatter volume, is accurate within 1% (i.e., the residual scatter signal is less than 1% of the primary signal) for field sizes up to 100 cm2 and air gaps over 30 cm, but shows significant discrepancies for larger field sizes. Monte Carlo results are presented showing that the effective multiple-scatter source is located toward the exit surface of the scatterer, rather than at its center. A second model is therefore investigated where second and higher-order scattering is instead modeled by fitting an analytical function describing a nonstationary isotropic point-scatter source to Monte Carlo generated data. This second model is shown to be accurate to within 1% for air gaps down to 20 cm, for field sizes up to 900 cm2 and phantom thicknesses up to 50 cm.

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“…To determine the appropriate air gap distance for the back detector, selectivity was calculated using the 'effective scatter source model suggested by Muntz, et al [23] and developed by Sorenson and Floch [18]. According to this model, scatter radiation behaves as if it originates from a point source located between the focal spot and the exit surface of the object.…”

Section: Air Gap Distance and Selectivitymentioning

confidence: 99%

Scatter removal using modified air gap method: spectral composition technique

1993

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A new scatter rejection technique using the modified air gap method is presented. Two x-ray cassettes are used per exposure. One cassette (front cassette) was placed immediately behind the object. The other (back cassette) was positioned 60 cm behind the object. Thefront radiograph has good spatial resolution but includes a relatively large amount of scatter. The back radiograph has poor high frequency resolution but little scatter due to the air gap. The spectral composition technique extracts highfrequency informationfrom thefront radiograph and combines it with the lowfrequency information of the back radiograph to produce an improved composite synthesized image. No artifacts due to the spectral composition technique were observed. In the lung and heart regions, the modified air gap method resulted in comparable or superior scatter rejection performance as compared to the conventional grid technique.

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Electronic Grids for Electrostatic Imaging Systems

Cited by 11 publications

References 12 publications

Task-based modeling and optimization of a cone-beam CT scanner for musculoskeletal imaging

Task-based modeling and optimization of a cone-beam CT scanner for musculoskeletal imaging

Analytical scatter kernels for portal imaging at 6 MV

Scatter removal using modified air gap method: spectral composition technique

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