Characterization of scatter in cone‐beam CT breast imaging: Comparison of experimental measurements and Monte Carlo simulation

Chen, Yu; Liu, Bob; O’Connor, J. Michael; Didier, Clay; Glick, Stephen J.

doi:10.1118/1.3077122

Cited by 61 publications

(79 citation statements)

References 36 publications

(32 reference statements)

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“…8,9,21 The discrepancy between the measurement and MC simulation is often ascribed to extra detector scatter. 20 In this study, we find that the scatter measurement can be more accurate with the proposed I 0 correction. As shown in Fig.…”

Section: Iiia Measurement Of Focal Spot Distribution and Detector Psfmentioning

confidence: 68%

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Relationship between x‐ray illumination field size and flat field intensity and its impacts on x‐ray imaging

et al. 2012

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Purpose: X-ray cone-beam CT (CBCT) is being increasingly used for various clinical applications, while its performance is still hindered by image artifacts. This work investigates a new source of reconstruction error, which is often overlooked in the current CBCT imaging. The authors find that the x-ray flat field intensity (I 0 ) varies significantly as the illumination volume size changes at different collimator settings. A wrong I 0 value leads to inaccurate CT numbers of reconstructed images as well as wrong scatter measurements in the CBCT research. Methods: The authors argue that the finite size of x-ray focal spot together with the detector glare effect cause the I 0 variation at different illumination sizes. Although the focal spot of commercial x-ray tubes typically has a nominal size of less than 1 mm, the off-focal-spot radiation covers an area of several millimeters on the tungsten target. Due to the large magnification factor from the field collimator to the detector, the penumbra effects of the collimator blades result in different I 0 values for different illumination field sizes. Detector glare further increases the variation, since one pencil beam of incident x-ray is scattered into an area of several centimeters on the detector. In this paper, the authors study these two effects by measuring the focal spot distribution with a pinhole assembly and the detector point spread function (PSF) with an edge-spread function method. The authors then derive a formula to estimate the I 0 value for different illumination field sizes, using the measured focal spot distribution and the detector PSF. Phantom studies are carried out to investigate the accuracy of scatter measurements and CT images with and without considering the I 0 variation effects. Results: On our tabletop system with a Varian Paxscan 4030CB flat-panel detector and a Varian RAD-94 x-ray tube as used on a clinical CBCT system, the focal spot distribution has a measured fullwidth-at-half-maximum (FWHM) of around 0.4 mm, while non-negligible off-focal-spot radiation is observed at a distance of over 2 mm from the center. The measured detector PSF has an FWHM of 0.510 mm, with a shape close to Gaussian. From these two distributions, the author calculate the estimated I 0 values at different collimator settings. The I 0 variation mainly comes from the focal spot effect. The estimation matches well with the measurements at different collimator widths in both horizontal and vertical directions, with an average error of less than 3%. Our method improves the accuracy of conventional scatter measurements, where the scatter is measured as the difference between fan-beam and cone-beam projections. On a uniform water cylinder phantom, more accurate I 0 suppresses the unfaithful high-frequency signals at the object boundaries of the measured scatter, and the SPR estimation error is reduced from 0.158 to 0.014. The proposed I 0 estimation also reduces the reconstruction error from about 20 HU on the Catphan c 600 phantom in the selected regions of interes...

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Section: Iiia Measurement Of Focal Spot Distribution and Detector Psfmentioning

confidence: 68%

“…In the published literature, the scatter signals in the cone-beam projection are measured as the difference of the two projections, with an implicit assumption that the I 0 distributions are unchanged in both projections. 11,20,21 These methods obtain inaccurate scatter measurements especially around the object boundary.…”

Section: Introductionmentioning

confidence: 99%

Relationship between x‐ray illumination field size and flat field intensity and its impacts on x‐ray imaging

et al. 2012

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“…17,18,[49][50][51][52] If other researchers are interested in using these phantoms, they are encouraged to contact the corresponding author.…”

Section: Discussionmentioning

confidence: 99%

Generation of voxelized breast phantoms from surgical mastectomy specimens

O’Connor

Das

Dider³

et al. 2013

Medical Physics

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Purpose:In the research and development of dedicated tomographic breast imaging systems, digital breast object models, also known as digital phantoms, are useful tools. While various digital breast phantoms do exist, the purpose of this study was to develop a realistic high-resolution model suitable for simulating three-dimensional (3D) breast imaging modalities. The primary goal was to design a model capable of producing simulations with realistic breast tissue structure. Methods: The methodology for generating an ensemble of digital breast phantoms was based on imaging surgical mastectomy specimens using a benchtop, cone-beam computed tomography system. This approach allowed low-noise, high-resolution projection views of the mastectomy specimens at each angular position. Reconstructions of these projection sets were processed using correction techniques and diffusion filtering prior to segmentation into breast tissue types in order to generate phantoms. Results: Eight compressed digital phantoms and 20 uncompressed phantoms from which an additional 96 pseudocompressed digital phantoms with voxel dimensions of 0.2 mm 3 were generated. Two distinct tissue classification models were used in forming breast phantoms. The binary model classified each tissue voxel as either adipose or fibroglandular. A multivalue scaled model classified each tissue voxel as percentage of adipose tissue (range 1%-99%). Power spectral analysis was performed to compare simulated reconstructions using the breast phantoms to the original breast specimen reconstruction, and fits were observed to be similar. Conclusions: The digital breast phantoms developed herein provide a high-resolution anthropomorphic model of the 3D uncompressed and compressed breast that are suitable for use in evaluating and optimizing tomographic breast imaging modalities. The authors believe that other research groups might find the phantoms useful, and therefore they offer to make them available for wider use.

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“…However, study focusing on fluoroscopy has not been found yet. Previous researches were concerned about the impact of scattered radiation on patient dose [10,11,14,16,17] and radiographic image quality [14,18,19] , and the physical properties of radiation [12,20] , but there has not been study on the occupational dose of radiology department staff. Besides, the results obtained in general X-ray study cannot represent validly in fluoroscopy because the properties of these two modalities are different.…”

Section: Clinical Applications Of Fluoroscopy and Its Radiation Dosementioning

confidence: 99%

“…The knowledge on the nature and geometric patterns of scattered radiation has long been inadequate and researchers have proposed different methods to identify the scattering properties based on different radiation sources. General X-ray machines, computed tomography and radionuclide imaging have been considered as the main foci in radiology studies [10][11][12][13][14][15] . However, study focusing on fluoroscopy has not been found yet.…”

Section: Clinical Applications Of Fluoroscopy and Its Radiation Dosementioning

confidence: 99%

Simulation, visualization and dosimetric validation of scatter radiation distribution under fluoroscopy settings

Chan

Cheung

et al. 2015

JBEI

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Objective: This study developed a three-dimensional visualization method for presenting the geometric pattern of the relative dose generated by Monte Carlo (MC) simulation and validated the simulated dose values against the physical measurement. Methods:In fluoroscopy and interventional radiology examinations, relatively high level of occupational dose is delivered to healthcare workers due to prolonged radiation exposure in imaging procedures. As the spatial difference in dose is never negligible, the scatter radiation distribution under fluoroscopic exposures is thus worth investigating. MC simulation is a sophisticated statistical method, which has been widely applied for modeling scatter radiation in general X-ray examination room. However, the application and validation of MC simulation under fluoroscopy setting have not been found yet. In this study, a stack of tissue equivalent slabs were used as the object under fluoroscopic irradiation. EGSnrc-based DOSXYZnrc code was applied to simulate the scatter dose distribution and the physical measurement of radiation dose was performed using an ionization chamber radiation detector.Results: At 19 representative locations taking into account the work area and radiosensitive organs of healthcare workers, the trend compliance of the simulated with the measured dose values was examined using the correlation analysis. A significant monotonic association between the MC simulation and physical measurement of dose values was identified (r s =0.822 and P<.01). At the same horizontal distance from the irradiation axis, it was observed that the air dose was relatively higher at the level of gonad region than at the eye level. Conclusions:The proposed visualization approach illustrates a three dimensional dose simulation in local display density, which arouses the awareness about prolonged radiation exposure in clinical environment. The reliability and validity of the simulation were examined.

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Characterization of scatter in cone‐beam CT breast imaging: Comparison of experimental measurements and Monte Carlo simulation

Cited by 61 publications

References 36 publications

Relationship between x‐ray illumination field size and flat field intensity and its impacts on x‐ray imaging

Relationship between x‐ray illumination field size and flat field intensity and its impacts on x‐ray imaging

Generation of voxelized breast phantoms from surgical mastectomy specimens

Simulation, visualization and dosimetric validation of scatter radiation distribution under fluoroscopy settings

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