Indirect Flat-panel Detector Research Articles

Evaluation of a Large Area, 83 μm Pixel Pitch Amorphous Selenium Indirect Flat Panel Detector.

Dual-layer detectors provide a low-cost solution to improved material decomposition and lesion differentiation in X-ray imaging, while eliminating motion artifacts from multiple exposures. Most designs utilize two indirect detectors with scintillators designed for low-energy and higher-energy detection and separated by a copper filter to harden the beam for high energy detection. To improve the performance of the bottom detector and lower dose requirements, we have previously proposed an alloyed amorphous selenium photodetector to achieve improved resolution and absorption at green wavelengths, better suited to high-performance scintillators such as CsI:Tl. In this work, we demonstrate a baseline prototype for the bottom layer-a continuous, large area 83 μm pixel pitch flat panel indirect detector with well-established amorphous selenium as the photodetector-and verify the architecture's performance and detector design. We characterize lag, noise-power spectrum, detective quantum efficiency, and modular transfer function of the detector, and show resolution up to 6 lp/mm when operated at an applied bias of 150 V. This provides a starting point for evaluating the alloyed selenium materials, and shows promise for this detector in the future dual-layer design.

Proper Management of the Clinical Exposure Index Based on Body Thickness Using Dose Optimization Tools in Digital Chest Radiography: A Phantom Study.

In radiography, the exposure index (EI), as per the International Electrotechnical Commission standard, depends on the incident beam quality and exposure dose to the digital radiography system. Today automatic exposure control (AEC) systems are commonly employed to obtain the optimal image quality. An AEC system can maintain a constant incident exposure dose on the image receptor regardless of the patient thickness. In this study, we investigated the relationship between body thickness, entrance surface dose (ESD), EI, and the exposure indicator (S value) with the aim of using EI as the dose optimization tool in digital chest radiography (posterior–anterior and lateral projection). The exposure condition from the Korean national survey for determining diagnostic reference levels and two digital radiography systems (photostimulable phosphor plate and indirect flat panel detector) were used. As a result, ESD increased as the phantom became thicker with constant exposure indicator, which indicates similar settings to an AEC system, but the EI indicated comparatively constant values without following the tendency of ESD. Therefore, body thickness should be considered under the AEC system for introducing EI as the dose optimization tool in digital chest radiography.

Scintillating glass‐ceramic substrates for indirect flat panel detectors in digital radiography

AbstractIndirect flat panel detectors (I‐FPDs) enable digital radiography at high X‐ray energies. However, the performance of these devices is limited due to the large number of X rays that pass through them undetected. The authors hypothesize that a glass‐based scintillator may serve as a substrate for the thin film transistors and photodiodes in an I‐FPD, leading to improvements in X‐ray detection for improved performance. The authors synthesized a series of five glass‐ceramic scintillators based on an oxyhalide glass matrix. Each glass ceramic contains barium chloride crystals which serve as scattering centers to prevent “light trapping” in the material; barium chloride is also a well‐known scintillation crystal. Four of the samples contain trivalent terbium, which serves as a second luminescent center. The light output of each sample was compared against a well‐known X‐ray scintillator, gadolinium oxysulfide (GOS) under RQA9 exposure conditions, in the back‐irradiation configuration. The addition of terbium oxide to the glass composition increases the detected light output, which varies by concentration. The thickness of the glass‐ceramic scintillator has a profound effect on performance, with the results influenced by such factors as self‐attenuation of emission in the thicker samples and decreased X‐ray capture in the thinner samples. The brightest sample tested achieved a light output 13% that of the GOS intensifier screen. The results indicate that the use of scintillating glass‐ceramic substrates should lead to increased performance in indirect digital radiography.

Correlation between physical measurements and observer evaluations of image quality in digital chest radiography.

The aim of this paper was to investigate the relationship between the physical and subjective (observer) image quality metrics in digital chest radiography. Five digital radiography systems, four with indirect flat panel detector and one with storage phosphor-based computed radiography system, were used in the study. The physical image quality assessments were carried out using effective detective quantum efficiency (eDQE) metric and subjective performance of the digital radiography systems was evaluated in terms of inverse image quality figure (IQFinv ) derived from the contrast-detail (CD) diagrams using CDRAD 2.0 phantom and CDRAD phantom analyzer software. All measurements were performed for different tube voltages (70, 81, 90, 102, 110, and 125kVp) and polymethyl methacrylate (PMMA) phantom thicknesses. An anthropomorphic chest phantom and visual grading analysis (VGA) technique based on European image quality criteria for chest radiography were used for clinical image quality evaluation. The Spearman correlation coefficients were calculated for the investigation of the correlation between physical image quality and clinical image quality. The results showed strong positive correlation between the physical and clinical image quality findings. The minimum correlation coefficient was 0.91 (p<0.011) for IQFinv vs VGA scores and 0.92 (p<0.009) for IeDQE vs VGA scores. Our results confirm that clinical image quality can be predicted with both physical assessments and contrast-detail detectability studies.

Combination system in advanced image processing for improving image contrast and a conventional row-ratio grid for an indirect flat-panel detector system: An experimental study

Conventional grids with high grid ratios are not ideal for use in bedside radiography because of the difficulty in maintaining the required alignment. To address this issue, the potential usefulness of a combination system that employs removal processing software for scattered radiation and a conventional grid with a low grid ratio (3:1) for an indirect-conversion-type flat-panel detector system was evaluated by measuring image quality and observer performance. The hypothetical grid ratios for the software were 2:1, 3:1, 6:1, 8:1, and 10:1. The scatter fraction of the combination system was lower than that of the software alone. Significant improvement was observed in the effect of scattered radiation removal up to a hypothetical software grid ratio of 6:1. However, the Wiener spectrum increased (radiographic noise degraded) with an increase in the hypothetical grid ratio. The contrast ratios of the combination system were improved compared to those of the software alone for anthropomorphic chest radiographs. An observer test was also conducted using the contrast-detail phantom. The combination system indicated higher low-contrast detectability compared to the software alone, although there were no statistical differences between the hypothetical grid ratios of 6:1, 8:1, and 10:1 in all combinations of the software alone and the combination system. We concluded that a combination system with software that uses a hypothetical grid ratio of 6:1 or more and a 3:1 conventional grid would be more useful for reducing the scattered radiation component compared to the software alone with a hypothetical higher grid ratio for thicker objects.

An apparatus and method for directly measuring the depth-dependent gain and spatial resolution of turbid scintillators.

Turbid (powder or columnar-structured) scintillators are widely used in indirect flat panel detectors (I-FPDs) for scientific, industrial, and medical radiography. Light diffusion and absorption within these scintillators is expected to cause depth-dependent variations in their x ray conversion gain and spatial blur. These variations degrade the detective quantum efficiency of I-FPDs at all spatial frequencies. Despite their importance, there are currently no established methods for directly measuring scintillator depth effects. This work develops the instrumentation and methods to achieve this capability. An ultra-high-sensitivity camera was assembled for imaging single x ray interactions in two commercial Gd2 O2 S:Tb (GOS) screens (Lanex Regular and Fast Back, Eastman Kodak Company). X ray interactions were localized to known depths in the screens using a slit beam of parallel synchrotron radiation (32keV), with beam width (~20μm) much narrower than the screen thickness. Depth-localized x ray interaction images were acquired in 30μm depth-intervals, and analyzed to measure each scintillator's depth-dependent average gain and modulation transfer function MTF(z,f). These measurements were used to calculate each screen's expected MTF(f) in an energy-integrating detector (e.g., I-FPD). Calculations were compared to presampling MTF measurements made by coupling each screen to a high-resolution CMOS image sensor (48μm pixel) and using the slanted-edge method. Both and MTF(z,f) continuously increased as interactions occurred closer to each screen's sensor-coupled surface. The Regular yielded 1351±66 and 2117±54 photons per absorbed x ray (42-66keV-1 ) in interactions occurring furthest from and nearest to the image sensor, while the Fast Back yielded 833±22 and 1910±39 photons (26-60keV-1 ). At f=1mm-1 , MTF(z,f) varied between 0.63 and 0.78 in the Regular and 0.30-0.76 in the Fast Back. Calculations of presampling MTF(f) using and MTF(z,f) showed excellent agreement with slanted-edge measurements. The developed instrument and method enable direct measurements of the depth-dependent gain and spatial resolution of turbid scintillators. This knowledge can be used to predict, understand, and potentially improve I-FPD imaging performance.

A novel radiation detector for removing scattered radiation in chest radiography: Monte Carlo simulation-based performance evaluation

Scattered radiation is the main reason for the degradation of image quality and the increased patient exposure dose in diagnostic radiology. In an effort to reduce scattered radiation, a novel structure of an indirect flat panel detector has been proposed. In this study, a performance evaluation of the novel system in terms of image contrast as well as an estimation of the number of photons incident on the detector and the grid exposure factor were conducted using Monte Carlo simulations. The image contrast of the proposed system was superior to that of the no-grid system but slightly inferior to that of the parallel-grid system. The number of photons incident on the detector and the grid exposure factor of the novel system were higher than those of the parallel-grid system but lower than those of the no-grid system. The proposed system exhibited the potential for reduced exposure dose without image quality degradation; additionally, can be further improved by a structural optimization considering the manufacturer's specifications of its lead contents.

Monte Carlo simulation-based feasibility study of novel indirect flat panel detector system for removing scatter radiation

The purpose of this study is to investigate the feasibility of a novel indirect flat panel detector (FPD) system for removing scatter radiation. The substrate layer of our FPD system has a Pb net-like structure that matches the ineffective area and blocks the scatter radiation such that only primary X-rays reach the effective area on a thin-film transistor. To evaluate the performance of the proposed system, we used Monte Carlo simulations to derive the scatter fraction and contrast. The scatter fraction of the proposed system is lower than that of a parallel grid system, and the contrast is superior to that of a system without a grid. If the structure of the proposed FPD system is optimized with respect to the specifications of a specific detector, the purpose of the examination, and the energy range used, the FPD can be useful in diagnostic radiology.

Imaging responses of on-site CsI and Gd2O2S flat-panel detectors: Dependence on the tube voltage

One of the emerging issues in radiography is low-dose imaging to minimize patient’s exposure. The scintillating materials employed in most indirect flat-panel detectors show a drastic change of X-ray photon absorption efficiency around their K-edge energies that consequently affects image quality. Using various tube voltages, we investigated the imaging performance of most popular scintillators: cesium iodide (CsI) and gadolinium oxysulfide (Gd2O2S). The integrated detective quantum efficiencies (iDQE) of four detectors installed in the same hospital were evaluated according to the standardized procedure IEC 62220-1 at tube voltages of 40 - 120 kVp. The iDQE values of the Gd2O2S detectors were normalized by those of CsI detectors to exclude the effects of image postprocessing. The contrast-to-noise ratios (CNR) were also evaluated by using an anthropomorphic chest phantom. The iDQE of the CsI detector outperformed that of the Gd2O2S detector over all tube voltages. Moreover, we noted that the iDQE of the Gd2O2S detectors quickly rolled off with decreasing tube voltage under 70 kVp. The CNRs of the two scintillators were similar at 120 kVp. At 60 kVp, however, the CNR of Gd2O2S was about half that of CsI. Compared to the Gd2O2S detectors, variations in the DQE performance of the CsI detectors were relatively immune to variations in the applied tube voltages. Therefore, we claim that Gd2O2S detectors are inappropriate for use in low-tube-voltage imaging (e.g., extremities and pediatrics) with low patient exposure.

SU-E-I-49: Simulation Study for Removing Scatter Radiation in Cesium-Iodine Based Flat Panel Detector System

Purpose: This study aims to identify the feasibility of a novel cesium-iodine (CsI)-based flat-panel detector (FPD) for removing scatter radiation in diagnostic radiology. Methods: The indirect FPD comprises three layers: a substrate, scintillation, and thin-film-transistor (TFT) layer. The TFT layer has a matrix structure with pixels. There are ineffective dimensions on the TFT layer, such as the voltage and data lines; therefore, we devised a new FPD system having net-like lead in the substrate layer, matching the ineffective area, to block the scatter radiation so that only primary X-rays could reach the effective dimension.To evaluate the performance of this new FPD system, we conducted a Monte Carlo simulation using MCNPX 2.6.0 software. Scatter fractions (SFs) were acquired using no grid, a parallel grid (8:1 grid ratio), and the new system, and the performances were compared.Two systems having different thicknesses of lead in the substrate layer—10 and 20μm—were simulated. Additionally, we examined the effects of different pixel sizes (153×153 and 163×163μm) on the image quality, while keeping the effective area of pixels constant (143×143μm). Results: In case of 10μm lead, the SFs of the new system (∼11%) were lower than those of the other system (∼27% with no grid, ∼16% with parallel grid) at 40kV. However, as the tube voltage increased, the SF of new system (∼19%) was higher than that of parallel grid (∼18%) at 120kV. In the case of 20μm lead, the SFs of the new system were lower than those of the other systems at all ranges of the tube voltage (40–120kV). Conclusion: The novel CsI-based FPD system for removing scatter radiation is feasible for improving the image contrast but must be optimized with respect to the lead thickness, considering the system's purposes and the ranges of the tube voltage in diagnostic radiology. This study was supported by a grant(K1422651) from Institute of Health Science, Korea University.

Comparison of the perceived image quality between two digital imaging systems for neonatal bedside radiography – A case study

BackgroundChest X-rays are performed daily in the neonatal intensive care and high care units. The skill of the radiographer is critical for obtaining the best image quality and limiting the patient's radiation exposure. The literature states that indirect flat panel detectors produce images of superior quality in comparison to computed radiography systems. At Steve Biko Academic Hospital a decision was made to revert from the direct digital radiography (DR) system to the computed radiography (CR) system, due to poor image quality experienced. MethodThe case study objective was to conduct a comparative analysis describing key technical factors contributing to image quality. The analysis entailed retrospectively comparing the images obtained during 2010 and 2011. An image analysis form was utilised in evaluating the technical aspects of the image. A total of 160 images were viewed by 16 participants sampled from the radiography, radiology and paediatric departments. The participants were asked to re-evaluate two of their allotted images after five days to determine their reliability. ResultsFindings were that the DR system provides significantly better image quality than the CR system (p < 0.05) for all the technical factors evaluated. However technical improvements are recommended. A wide variance in intra-observer reliability was also found. ConclusionThis case study demonstrated that DR images were considered to be superior to CR images. Recommendations include: a standardised technique for imaging the neonates; optimisation of the imaging software for the digital detectors, improved feedback systems in terms of exposure index values, and the training of radiographers and referring physicians in technical image analysis.

Detectability of simulated pulmonary nodules on chest radiographs: Comparison between irradiation side sampling indirect flat-panel detector and computed radiography

ObjectiveTo compare the detectability of simulated pulmonary nodules on chest radiographs between an irradiation side sampling indirect flat-panel detector (ISS-FPD) and computed radiography (CR). Materials and methodsThis study was an observer performance study. Simulated pulmonary nodules of 8mm in diameter were superimposed on an anthropomorphic chest phantom. Chest radiographs were acquired under 2 exposure levels (4 and 3.2mAs) with the ISS-FPD and the CR. Six thoracic radiologists evaluated all 40 images (10 patterns×2 different exposure doses×2 different systems) for the presence or absence of a lesion over each of 12 defined areas on a 3-megapixel monochrome liquid-crystal display. Receiver operating characteristic (ROC) curves were obtained for observation in predefined 480 areas. A jackknife method was used for statistical analysis. Differences with a P value of <0.05 were considered significant. ResultsThe analysis of the observer detection of simulated pulmonary nodules showed larger areas under the ROC curve (AUC) by the ISS-FPD than by the CR. There was a statistically significant difference between the two systems at 3.2mAs (P=0.0330). ConclusionThe ISS-FPD was superior to the CR for the detection of simulated pulmonary nodules at 3.2mAs.

Assessment of multi-directional MTF for breast tomosynthesis

A method was developed to assess the multi-directional modulation transfer function (MTF) of breast tomosynthesis imaging systems using a sphere phantom. The method was initially developed based on a simulation dataset. Projections were simulated for a uniform voxelized breast phantom with sphere inserts using a fluence modeled from a 28 kVp beam incident upon an indirect flat-panel detector. Based on cascaded systems modeling, characteristic noise and blurring were added to each projection. The projections were reconstructed using a standard filtered backprojection technique, producing a 3D volume with an isotropic voxel size of 200 µm. ROIs that completely encompassed single spheres were extracted and conical regions were prescribed along the three major axes extending from the centroids. Pixels within the cones were used to form edge spread functions (ESFs), from which the directional MTFs were calculated. Binning size and conical range were adjusted to maximize the accuracy and to minimize the noise of the MTF. A method was further devised to remove out-of-plane artifacts from the ESF in the x–y plane. Finally, the method was applied to experimentally assess the directional MTF of a prototype tomosynthesis system. Comparisons of the sphere-based MTF along the different axes and the theoretical MTF yielded good agreement. A 30° angular cone and a 20 µm sampling were found to provide an ideal trade-off between the noise and accuracy of the measurement. The removal of artifacts in ESF yielded ‘modified’ MTFs that enabled a resolution-only characterization of the in-slice resolution of tomosynthesis. Drop-off frequencies in the x- and y-directional MTFs were 1.6 cycles mm−1 and 1.5 cycles mm−1, respectively. The presented method of separating the effective resolution and artifacts from the measured ESF was found experimentally implementable and is expected to facilitate the interpretation of MTF measurements in tomosynthesis.

Basic imaging properties of an indirect flat-panel detector system employing irradiation side sampling (ISS) technology for chest radiography: comparison with a computed radiographic system

The image quality and potential usefulness for patient skin-dose reduction of a newly developed flat-panel detector (FPD) system employing irradiation side sampling (ISS) were investigated and compared to a conventional computed radiography (CR) system. We used the X-ray beam quality of RQA 9 as noted in the standard evaluation method by the International Electrotechnical Commission 62220-1 to evaluate the image quality of the detector for chest radiography. The presampled modulation transfer function (MTF) of the ISS-FPD system was slightly higher than that of the CR system in the horizontal direction at more than 2.2 cycles/mm. However, the presampled MTF of the ISS-FPD system was slightly lower than that of the CR system in the vertical direction. The Wiener spectrum of the ISS-FPD system showed a 50-65 % lesser noise level than that of the CR system under the same exposure condition. The detective quantum efficiency of the ISS-FPD system was at least twice as great as that of the CR system. We conclude that the ISS-FPD system has the potential to reduce the patient skin dose compared to a conventional CR system for chest radiography.

SU-E-I-188: Potential for Dose Reduction in An Indirect Flat Panel Detector System Employing Irradiation Side Sampling

Purpose: To investigate possibility of dose reduction for a newly developed indirect flat panel detector(FPD)system employing irradiation side sampling (ISS), physical imaging properties were measured and compared with those of a conventional computed radiography(CR)system. Method and Materials:The FPDsystem employing ISS (CALNEO MT, Fuji Film) and the CRsystem (FCR PROFECT CS, Fuji Film) including the imaging plate (ST‐VI, Fuji Film) were used in this study. The Wiener spectrum (WS), the presampled modulation transfer function(MTF), and the detective quantum efficiency (DQE) for both systems were measured. To evaluate image quality of the detector for chest radiography, the RQA 9 in the International Electrotechnical Commission (IEC) 62220‐1 was used. Results: The WS of the FPDsystem showed considerably lower than that of the CRsystem at every spatial frequency. The WS of the FPDsystem with a 50 % dose reduction of the CRsystem was almost identical to that of the CRsystem. The presampled MTF of the FPDsystem was comparable to that of the CRsystem. The DQE of the FPDsystem obtained at zero spatial frequency was almost twice than that of the CRsystem. Conclusion: The radiographic noise property and the detection efficiency of the new ISS FPD were significantly superior to those of the conventional CRsystem. It is expected that the use of the new ISS FPDsystem for chest radiography can reduce the patient skin dose by 50 % compared with the conventional CRsystem.

SU-E-I-186: Digital Radiography Artifacts

Purpose: Recent and rapid development in digital radiography (DR) systems has led to greater flexibility in DR usage. With new DR uses, new processing algorithms, new acquisition tools and methods we see new artifacts, and some old artifacts with new presentations. In this poster we present a host of DR artifacts and their explanations, along with tips for identifying or avoiding them. Methods: DR artifacts were collected over the course of several years from four different vendor equipment models used for routine chest, general and portable radiography. Both fixed and wireless indirect flat panel detector images are included. The acquisition conditions for each image are described or approximated from knowledge of standard acquisition techniques. Results: Artifact examples in our poster include those due to: image lag, flawed gain calibration, image-lag + flawed dark-noise correction, backscatter through a portable detector and stitching issues. The underlying physics which contributed to each artifact is explained to the degree that is possible without knowledge of proprietary vendor algorithms and techniques. Several of the artifacts presented had the potential to impact diagnosis. Suggested techniques for preventing the artifacts or quality control steps to avoid such artifact formation are also provided. Conclusions: Before purchasing a DR system, upgrading to DR, or using DR, it is important to be aware of its limitations, some of which result in image artifact formation. In this poster, we present several example artifacts which have not previously received attention, are unique to DR, or present differently than in computed radiography (CR). Knowledge of how these artifacts form, their frequency and severity are important considerations for DR use, selection, acceptance testing and quality control.

直接型および間接型Ｆｌａｔ Ｐａｎｅｌ Ｄｅｔｅｃｔｏｒｓと Ｃｏｍｐｕｔｅｄ Ｒａｄｉｏｇｒａｐｈｙにおける物理的画質評価を利用した画質同一化の試み

The purpose of this study was to investigate image quality identification methods among direct- and indirect-type flat panel detectors (FPDs) and a computed radiography (CR) system using two radiation qualities RQA3 and RQA5 defined in the IEC 61267 standard. For each system, the digital characteristic curve, the presampled modulation transfer function (MTF), and the normalized noise power spectrum (NNPS) were measured. Images for a burger phantom and a foot-bone phantom were processed by resolution identification utilizing two-dimensional Fourier transform, and then contrast-to-noise ratio (CNR) for each image was measured. For the RQA3, the direct FPD system indicated the highest DQE value, and for the RQA5 DQE value of indirect FPD system, it was a little higher than that of direct FPD system. The CNR results with the resolution identification displayed good accordance with the DQE results in both phantoms. From the DQE results, dose ratios for image quality identification were determined, and the CNRs of the dose-adjusted images were measured. The results for, the CNRs of all systems showed good coincidence. From these findings, they indicated that the DQE measurement is effective to determine the exposure parameters for equalizing the image quality of different types of radiographic systems.

直接，間接変換方式の違いにおけるフラットパネルディテクタのノイズ特性の比較

Flat-panel detector (FPD) digital radiography systems have direct and indirect conversion systems, and the 2 conversion systems provide different imaging performances. We measured some imaging performances [input-output characteristic, presampled modulation transfer function (presampled MTF), noise power spectrum (NPS)] of direct and indirect FPD systems. Moreover, some image samples of the NPSs were visually evaluated by the pair comparison method. As a result, the presampled MTF of the direct FPD system was substantially higher than that of the indirect FPD system. The NPS of the direct FPD system had a high value for all spatial frequencies. In contrast, the NPS of the indirect FPD system had a lower value as the frequency became higher. The results of visual evaluations showed the same tendency as that found for NPSs. We elucidated the cause of the difference in NPSs in a simulation study, and we determined that the cause of the difference in the noise components of the direct and indirect FPD systems was closely related to the presampled MTF.

SU‐FF‐I‐139: Low Dose Breast CT with Photon Counting Detectors: A Phantom Study

Purpose: To investigate image quality improvement of breast computed tomography (CT) using a photon counting detector as compared to an energy integrating flat panel detector. Method and Materials: A cone‐beam CT system was built that utilized a CsI‐based flat panel detector. The system consisted of a standard tungsten target x‐ray tube and a CsI indirect flat panel detector (Paxscan 4030CB) mounted on an optical bench. The photon counting CT system was built with the same setup, but with the flat panel detector replaced by a row of cadmium. (CZT) detector (eV2500, eV Products). The CZT detector consisted of 64 pixels with a pitch of 0.8 mm and five energy bins for spectral separation. A Lucite phantom (2.5 cm in diameter) was constructed with iodine and calcium contrast materials. Tomographic data were acquired with both systems and the contrast‐to‐noise ratio was compared. The data from CZT was energy weighted before analysis. Results: Image quality improved when comparing the CZT energy weighted images to flat panel images. The CNR improvements were 24% and 19% for calcium and iodine, respectively. Conclusions: Phantom results showed significant improvement in CNR for breast CT using an energy resolving photon counting detector as compared with an energy integrating flat panel detector.

Effect of Oblique X-ray Incidence in Flat-Panel Computed Tomography of the Breast

We quantify the variation in resolution due to anisotropy caused by oblique X-ray incidence in indirect flat-panel detectors for computed tomography breast imaging systems. We consider a geometry and detector type utilized in breast computed tomography (CT) systems currently being developed. Our methods rely on mantis, a combined X-ray, electron, and optical Monte Carlo transport open source code. The physics models are the most accurate available in general-purpose Monte Carlo packages in the diagnostic energy range. We consider maximum-obliquity angles of 10 ( degrees ) and 13 ( degrees ) at the centers of the 30 and 40 cm detector edges, respectively, and 16 ( degrees ) at the corner of the detector. Our results indicate that blur is asymmetric and that the resolution properties vary significantly with the angle (or location) of incidence. Our results suggest that the asymmetry can be as high as a factor of 2.6 between orthogonal directions. Anisotropy maps predicted by mantis provide an understanding of the effect that such variations have on the imaging system and allow more accurate modeling and optimization of breast CT systems. These maps of anisotropy across the detector could lead to improved reconstruction and help motivate physics-based strategies for computer detection of breast lesions.