Background Amyloid deposits in the temporal and frontal lobes in patients with Alzheimer’s diseas... more Background Amyloid deposits in the temporal and frontal lobes in patients with Alzheimer’s disease make them potential targets to aid in early diagnosis. Recently, spectral small-angle X-ray scattering techniques have been proposed for interrogating deep targets such as amyloid plaques. Results We describe an optimization approach for the orientation of beams for deep target characterization. The model predicts the main features of scattering profiles from targets with varying shape, size and location. We found that increasing target size introduced additional smearing due to location uncertainty, and incidence angle affected the scattering profile by altering the path length or effective target size. For temporal and frontal lobe targets, beam effectiveness varied up to 2 orders of magnitude. Conclusions Beam orientation optimization might allow for patient-specific optimal paths for improved signal characterization.
Imaging clinical trials can be burdensome and often delay patient access to novel, high-quality m... more Imaging clinical trials can be burdensome and often delay patient access to novel, high-quality medical devices. Tools for in silico imaging trials have significantly improved in sophistication and availability. Here, I describe some of the principal advantages of in silico imaging trials and enumerate five lessons learned during the design and execution of the first all-in silico virtual imaging clinical trial for regulatory evaluation (the VICTRE study).
New display applications for the interpretation of medical images include mobile image viewers, t... more New display applications for the interpretation of medical images include mobile image viewers, true-color modalities, and 3-D technologies for improved diagnostic performance.
Monte Carlo simulations require large number of histories to obtain reliable estimates of the qua... more Monte Carlo simulations require large number of histories to obtain reliable estimates of the quantity of interest and its associated statistical uncertainty. Numerous variance reduction techniques (VRTs) have been employed to increase computational efficiency by reducing the statistical uncertainty. We investigate the effect of two VRTs for optical transport methods on accuracy and computing time for the estimation of variance (noise) in x-ray imaging detectors. We describe two VRTs. In the first, we preferentially alter the direction of the optical photons to increase detection probability. In the second, we follow only a fraction of the total optical photons generated. In both techniques, the statistical weight of photons is altered to maintain the signal mean. We use fastdetect2, an open-source, freely available optical transport routine from the hybridmantis package. We simulate VRTs for a variety of detector models and energy sources. The imaging data from the VRT simulations ...
Challenges are emerging with regard to the pre-clinical, regulatory assessment of display systems... more Challenges are emerging with regard to the pre-clinical, regulatory assessment of display systems used for viewing and interpreting medical images. This article discusses those, and also the types of evidence that might be relevant to the evaluation of mobile image-viewing devices, true-color devices with applications in digital microscopy, and 3-D medical displays as discussed in Part 1.
This work studies the detective quantum efficiency (DQE) of a-Se-based solid state x-ray detector... more This work studies the detective quantum efficiency (DQE) of a-Se-based solid state x-ray detectors for medical imaging applications using ARTEMIS, a Monte Carlo simulation tool for modeling x-ray photon, electron and charged carrier transport in semiconductors with the presence of applied electric field. ARTEMIS is used to model the signal formation process in a-Se. The simulation model includes x-ray photon and high-energy electron interactions, and detailed electron-hole pair transport with applied detector bias taking into account drift, diffusion, Coulomb interactions, recombination and trapping. For experimental validation, the DQE performance of prototype a-Se detectors is measured following IEC Testing Standard 62220-1-3. Comparison of simulated and experimental DQE results show reasonable agreement for RQA beam qualities. Experimental validation demonstrated within 5% percentage difference between simulation and experimental DQE results for spatial frequency above 0.25 cycle...
Medical Imaging 2016: Physics of Medical Imaging, 2016
We propose a new design of a stacked three-layer flat-panel x-ray detector for dual-energy (DE) i... more We propose a new design of a stacked three-layer flat-panel x-ray detector for dual-energy (DE) imaging. Each layer consists of its own scintillator of individual thickness and an underlying thin-film-transistor-based flat-panel. Three images are obtained simultaneously in the detector during the same x-ray exposure, thereby eliminating any motion artifacts. The detector operation is two-fold: a conventional radiography image can be obtained by combining all three layers' images, while a DE subtraction image can be obtained from the front and back layers' images, where the middle layer acts as a mid-filter that helps achieve spectral separation. We proceed to optimize the detector parameters for two sample imaging tasks that could particularly benefit from this new detector by obtaining the best possible signal to noise ratio per root entrance exposure using well-established theoretical models adapted to fit our new design. These results are compared to a conventional DE temporal subtraction detector and a single-shot DE subtraction detector with a copper mid-filter, both of which underwent the same theoretical optimization. The findings are then validated using advanced Monte Carlo simulations for all optimized detector setups. Given the performance expected from initial results and the recent decrease in price for digital x-ray detectors, the simplicity of the three-layer stacked imager approach appears promising to usher in a new generation of multi-spectral digital x-ray diagnostics.
The display of monochrome medical images requires that luminance verus display value be calibrate... more The display of monochrome medical images requires that luminance verus display value be calibrated to provide good contrast at all brightness levels. Industry standards provide a specific grayscale curve for the calibration of display devices. The grayscale standard is derived from human perception data and is significantly different than the intrinsic luminance response of a cathode ray tube. Accurate calibration of a device usually requires that the display values be transformed and converted to a video signal using a 10 or 12 bit digital to analogue converter (DAC). We have developed an alternative method that uses the three 8 bit channels of a color graphic controller to achieve precise calibration. The method is demonstrated using a monitor having a video circuit to combine the red, green, and blue video signals with unequal weighting to form a monochrome video signal. Calibration is achieved by modifying the blue channel (10% video influence). Performance equivalent to an 11 bit DAC is demonstrated. The method is applicable to flat panel display devices.
The authors discuss measurement methods and instrumentation useful for the characterization of th... more The authors discuss measurement methods and instrumentation useful for the characterization of the gray tracking performance of medical color monitors for diagnostic applications. The authors define gray tracking as the variability in the chromaticity of the gray levels in a color monitor. The authors present data regarding the capability of color measurement instruments with respect to their abilities to measure a target white point corresponding to the CIE Standard Illuminant D65 at different luminance values within the grayscale palette of a medical display. The authors then discuss evidence of significant differences in performance among color measurement instruments currently available for medical physicists to perform calibrations and image quality checks for the consistent representation of color in medical displays. In addition, the authors introduce two metrics for quantifying grayscale chromaticity consistency of gray tracking. The authors' findings show that there is ...
The computational modeling of medical imaging systems often requires obtaining a large number of ... more The computational modeling of medical imaging systems often requires obtaining a large number of simulated images with low statistical uncertainty which translates into prohibitive computing times. We describe a novel hybrid approach for Monte Carlo simulations that maximizes utilization of CPUs and GPUs in modern workstations. We apply the method to the modeling of indirect x-ray detectors using a new
We report on a Monte Carlo method for modeling light transport phenomena in multilayer organic po... more We report on a Monte Carlo method for modeling light transport phenomena in multilayer organic polymer light-emitting devices on plastic flexible substrates. The method allows modeling of Cartesian geometrical structures describing the fate of photons through multiple scattering events determined by the wavelength-dependent material optical properties. We apply the method to analyze the wavelength distribution of emitted light spectra. We find that for all organic polymers considered, the light emission is slightly shifted toward the longer wavelengths, and that this shift is maximum for light emissions with peaks around 530 nm. The photon extraction efficiency is higher (0.430) for organic polymers emitting in the longer wavelengths, while the photon absorbed fraction is higher (0.676) for spectra with a maximum in the short wavelengths.
Background Amyloid deposits in the temporal and frontal lobes in patients with Alzheimer’s diseas... more Background Amyloid deposits in the temporal and frontal lobes in patients with Alzheimer’s disease make them potential targets to aid in early diagnosis. Recently, spectral small-angle X-ray scattering techniques have been proposed for interrogating deep targets such as amyloid plaques. Results We describe an optimization approach for the orientation of beams for deep target characterization. The model predicts the main features of scattering profiles from targets with varying shape, size and location. We found that increasing target size introduced additional smearing due to location uncertainty, and incidence angle affected the scattering profile by altering the path length or effective target size. For temporal and frontal lobe targets, beam effectiveness varied up to 2 orders of magnitude. Conclusions Beam orientation optimization might allow for patient-specific optimal paths for improved signal characterization.
Imaging clinical trials can be burdensome and often delay patient access to novel, high-quality m... more Imaging clinical trials can be burdensome and often delay patient access to novel, high-quality medical devices. Tools for in silico imaging trials have significantly improved in sophistication and availability. Here, I describe some of the principal advantages of in silico imaging trials and enumerate five lessons learned during the design and execution of the first all-in silico virtual imaging clinical trial for regulatory evaluation (the VICTRE study).
New display applications for the interpretation of medical images include mobile image viewers, t... more New display applications for the interpretation of medical images include mobile image viewers, true-color modalities, and 3-D technologies for improved diagnostic performance.
Monte Carlo simulations require large number of histories to obtain reliable estimates of the qua... more Monte Carlo simulations require large number of histories to obtain reliable estimates of the quantity of interest and its associated statistical uncertainty. Numerous variance reduction techniques (VRTs) have been employed to increase computational efficiency by reducing the statistical uncertainty. We investigate the effect of two VRTs for optical transport methods on accuracy and computing time for the estimation of variance (noise) in x-ray imaging detectors. We describe two VRTs. In the first, we preferentially alter the direction of the optical photons to increase detection probability. In the second, we follow only a fraction of the total optical photons generated. In both techniques, the statistical weight of photons is altered to maintain the signal mean. We use fastdetect2, an open-source, freely available optical transport routine from the hybridmantis package. We simulate VRTs for a variety of detector models and energy sources. The imaging data from the VRT simulations ...
Challenges are emerging with regard to the pre-clinical, regulatory assessment of display systems... more Challenges are emerging with regard to the pre-clinical, regulatory assessment of display systems used for viewing and interpreting medical images. This article discusses those, and also the types of evidence that might be relevant to the evaluation of mobile image-viewing devices, true-color devices with applications in digital microscopy, and 3-D medical displays as discussed in Part 1.
This work studies the detective quantum efficiency (DQE) of a-Se-based solid state x-ray detector... more This work studies the detective quantum efficiency (DQE) of a-Se-based solid state x-ray detectors for medical imaging applications using ARTEMIS, a Monte Carlo simulation tool for modeling x-ray photon, electron and charged carrier transport in semiconductors with the presence of applied electric field. ARTEMIS is used to model the signal formation process in a-Se. The simulation model includes x-ray photon and high-energy electron interactions, and detailed electron-hole pair transport with applied detector bias taking into account drift, diffusion, Coulomb interactions, recombination and trapping. For experimental validation, the DQE performance of prototype a-Se detectors is measured following IEC Testing Standard 62220-1-3. Comparison of simulated and experimental DQE results show reasonable agreement for RQA beam qualities. Experimental validation demonstrated within 5% percentage difference between simulation and experimental DQE results for spatial frequency above 0.25 cycle...
Medical Imaging 2016: Physics of Medical Imaging, 2016
We propose a new design of a stacked three-layer flat-panel x-ray detector for dual-energy (DE) i... more We propose a new design of a stacked three-layer flat-panel x-ray detector for dual-energy (DE) imaging. Each layer consists of its own scintillator of individual thickness and an underlying thin-film-transistor-based flat-panel. Three images are obtained simultaneously in the detector during the same x-ray exposure, thereby eliminating any motion artifacts. The detector operation is two-fold: a conventional radiography image can be obtained by combining all three layers' images, while a DE subtraction image can be obtained from the front and back layers' images, where the middle layer acts as a mid-filter that helps achieve spectral separation. We proceed to optimize the detector parameters for two sample imaging tasks that could particularly benefit from this new detector by obtaining the best possible signal to noise ratio per root entrance exposure using well-established theoretical models adapted to fit our new design. These results are compared to a conventional DE temporal subtraction detector and a single-shot DE subtraction detector with a copper mid-filter, both of which underwent the same theoretical optimization. The findings are then validated using advanced Monte Carlo simulations for all optimized detector setups. Given the performance expected from initial results and the recent decrease in price for digital x-ray detectors, the simplicity of the three-layer stacked imager approach appears promising to usher in a new generation of multi-spectral digital x-ray diagnostics.
The display of monochrome medical images requires that luminance verus display value be calibrate... more The display of monochrome medical images requires that luminance verus display value be calibrated to provide good contrast at all brightness levels. Industry standards provide a specific grayscale curve for the calibration of display devices. The grayscale standard is derived from human perception data and is significantly different than the intrinsic luminance response of a cathode ray tube. Accurate calibration of a device usually requires that the display values be transformed and converted to a video signal using a 10 or 12 bit digital to analogue converter (DAC). We have developed an alternative method that uses the three 8 bit channels of a color graphic controller to achieve precise calibration. The method is demonstrated using a monitor having a video circuit to combine the red, green, and blue video signals with unequal weighting to form a monochrome video signal. Calibration is achieved by modifying the blue channel (10% video influence). Performance equivalent to an 11 bit DAC is demonstrated. The method is applicable to flat panel display devices.
The authors discuss measurement methods and instrumentation useful for the characterization of th... more The authors discuss measurement methods and instrumentation useful for the characterization of the gray tracking performance of medical color monitors for diagnostic applications. The authors define gray tracking as the variability in the chromaticity of the gray levels in a color monitor. The authors present data regarding the capability of color measurement instruments with respect to their abilities to measure a target white point corresponding to the CIE Standard Illuminant D65 at different luminance values within the grayscale palette of a medical display. The authors then discuss evidence of significant differences in performance among color measurement instruments currently available for medical physicists to perform calibrations and image quality checks for the consistent representation of color in medical displays. In addition, the authors introduce two metrics for quantifying grayscale chromaticity consistency of gray tracking. The authors' findings show that there is ...
The computational modeling of medical imaging systems often requires obtaining a large number of ... more The computational modeling of medical imaging systems often requires obtaining a large number of simulated images with low statistical uncertainty which translates into prohibitive computing times. We describe a novel hybrid approach for Monte Carlo simulations that maximizes utilization of CPUs and GPUs in modern workstations. We apply the method to the modeling of indirect x-ray detectors using a new
We report on a Monte Carlo method for modeling light transport phenomena in multilayer organic po... more We report on a Monte Carlo method for modeling light transport phenomena in multilayer organic polymer light-emitting devices on plastic flexible substrates. The method allows modeling of Cartesian geometrical structures describing the fate of photons through multiple scattering events determined by the wavelength-dependent material optical properties. We apply the method to analyze the wavelength distribution of emitted light spectra. We find that for all organic polymers considered, the light emission is slightly shifted toward the longer wavelengths, and that this shift is maximum for light emissions with peaks around 530 nm. The photon extraction efficiency is higher (0.430) for organic polymers emitting in the longer wavelengths, while the photon absorbed fraction is higher (0.676) for spectra with a maximum in the short wavelengths.
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