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• A displacement-based damping identification method is proposed for low-frequency dominant structures. • The method uses the dynamic displacement reconstructed from acceleration by FFIR filter. • Displacement reconstruction effectively suppressed high-mode components in response. • The method identifies the damping of fundamental modes even with a small model order. • The effectiveness is validated by the application to a cable-stayed bridge in operation. This paper proposes a new concept for the estimation of modal damping ratios. This new concept is based on an operational modal analysis (OMA) technique that uses dynamic displacement reconstructed from measured acceleration. The reconstructed displacement physically suppresses the high-mode components in measured acceleration data and leads to modal participant factors that are sequentially arranged from low- to high-frequency modes. Thus, compared with the conventional approach that utilizes acceleration data, the proposed procedure provides a more reliable and robust damping estimate regardless of the model order selection. Furthermore, the use of reconstructed displacement guarantees the equilibrium of the system all the time. The OMA adopts a natural excitation technique (NExT) combined with an eigensystem realization algorithm (ERA). A finite element method (FEM)-based finite impulse response filter is adopted to reconstruct the dynamic displacement. The effectiveness and accuracy of the proposed approach is demonstrated for low-frequency dominant structures by using the numerical simulation study of a 9-story shear building and an actual field test of a cable-stayed bridge under operation in Korea. These examples allow a comparison of modal damping ratio estimates using reconstructed displacement and accelerations. [ABSTRACT FROM AUTHOR]

This paper describes an investigation which was done on prematurely failed pins used in die-casting dies for aluminum engine blocks. To investigate the causes of the failures, static and fatigue strength evaluations of the pin materials and the deterioration degree of the strength due to exposure to high temperatures were evaluated. SEM observations of the fracture surfaces of broken pins revealed that the fractures were the fatigue failure type caused by thermal stresses upon thermal expansion and cooling during the repeated die-casting process. A solidification analysis of the die-casting process was conducted to determine the temperature distribution of the dies and pins, and a coupled thermal-structure analysis was carried out using the temperature distribution information to determine the magnitude of the thermal stress in the pin. The maximum thermal stresses were used to predict the fatigue lifetime of the pin. The result of this investigation reveals that cooling holes at the center of the pin were machined with some degree of eccentricity, leading to a concentration of the thermal stress at the thin part and, ultimately resulting in a premature failure. Appropriate machining of a cooling hole in the die pins must be carried out in order to avoid premature failures of these components. • Pins used in die-casting dies for aluminum engine blocks prematurely failed. • Fracture surfaces of broken pins are the fatigue failure caused by thermal stress. • Coupled thermal-structure analysis was carried out to determine the thermal stress • Cooling holes with eccentricity caused a concentration of the thermal stress. [ABSTRACT FROM AUTHOR]

• A differential load cell is developed with a novel Wheatstone bridge circuit. • The inertia of the specimen is automatically negated during measurements. • A finite element model of the load cell is constructed and analyzed. • A prototype of the differential load cell is fabricated. • Shake table and wind tunnel tests are conducted. Load cells, also referred to as force transducers, are widely used in various engineering fields for measuring forces and torques. When load cells measure the forces of moving specimens, the measured force includes the inertia of the specimen. However, in applications where the objective is to quantify the resultant force without the contribution of the specimen's inertia, additional sensors are required, which can result in reduced accuracy or inadequate measurement. To address the inertia coupling effect, this study proposes a new sensor, called a "differential load cell," by combining two load cells using a novel Wheatstone bridge design. The primary load cell measures both the force of interest and the specimen's inertia, while the dummy load cell only measures the latter. The proposed Wheatstone bridge automatically negates the inertia, thereby addressing the coupling effect. Validation tests including wind tunnel experiments are conducted to examine the practicality and applicability of the differential load cell. [ABSTRACT FROM AUTHOR]

Digital tomosynthesis (DTS) is an X-ray imaging technique that produces cross-sectional images with a scanning motion in narrow angular ranges. This method is promising for the inspection of internal defects in thin slab objects, such as printed circuit boards. However, this limited angular scan approach can have limited resolution in the depth direction. In addition, it can cause ghosting artifacts that originate from other planes in the reconstructed plane. In this paper, we characterized the imaging performance of a DTS method that uses the filtered backprojection for reconstruction. Various imaging parameters were examined, such as the total scan angle and the number of projections used for the reconstruction. We analyzed the signal and noise characteristics of the reconstructed images obtained for a thin tungsten wire and a thin aluminum disc. We obtained in-plane and in-depth modulation transfer functions (MTFs) from the reconstructed wire response images. From the reconstructed disc response images, we calculated the signal difference between the disc region and the adjacent background region along the depth direction, which is called the artifact spread function (ASF). A narrow angular scan enhances the in-plane MTF performance compared to that obtained from the conventional computed tomography, but it degrades the in-depth MTF performance (i.e., it decreases the depth resolution). In addition, the narrow angular scan degrades the ASF performance and causes severe out-of-plane blur artifacts. The optimal scanning angular range is, therefore, required to obtain tomographic images with high spatial resolution and less blur artifacts. The analysis method performed in this paper could be useful for this optimization. [ABSTRACT FROM PUBLISHER]

The X-ray imaging performance of a phosphor-coupled photodiode array detector was assessed for use in a cone-beam computed tomography (CBCT) system for printed-circuit board inspection. The radiographic image quality of a detector is mainly responsible for the tomographic image quality. The radiographic image quality can be improved by increasing the X-ray exposure level, but CT scans at higher exposure can impose an enormous heat load on the X-ray tube. In this study, the detective quantum efficiency (DQE) was used to describe the image quality per air kerma as a metric to assess the detector performance. Measurement results were obtained for 40-kVp and 50-kVp tungsten-target X-ray beams, which show that the DQE of the detector is tolerant of air kerma levels as low as 0.8 μ Gy. Below this level, the electronic noise of the detector system could degrade the DQE performance. The concept of DQE and the measurement procedure are described, including the modulation-transfer function and the noise-power spectrum. [ABSTRACT FROM AUTHOR]

Purpose Acquisition of high-quality x-ray images using low patient exposures requires detectors with high detective quantum efficiency ( DQE). We describe a novel apodized-aperture pixel ( AAP) design that increases high-frequency modulation transfer function ( MTF) and DQE values. The AAP design makes a separation of physical sensor elements from image pixels by using very small sensor elements (e.g., 0.010-0.025 mm) to synthesize desired larger image pixels (e.g., 0.1-0.2 mm). Methods A cascaded systems model of signal and noise propagation is developed to describe the benefits of the AAP approach in terms of the MTF, Wiener noise power spectrum ( NPS), and DQE. The theoretical model was validated experimentally using a CMOS/CsI detector with 0.05 mm sensor elements to synthesize 0.20 mm image pixels and a clinical Se detector with 0.07 mm sensor elements to synthesize 0.28 mm pixels. A Monte Carlo study and x-ray images of a star-pattern and rat leg are used to visually compare AAP images. Results When used with a high-resolution converter layer and sensor elements one quarter the size of image pixels, the MTF is increased by 53% and the DQE by a factor of 2.3× at the image sampling cut-off frequency. Both simulated and demonstration images show improved detectability of high-frequency content and removal of aliasing artifacts. Evidence of Gibbs ringing is sometimes seen near high-contrast edges. Conclusions It is shown that the AAP approach preserves the MTF of the small sensor elements and attenuates frequencies above the image sampling cut-off frequency. This has the double benefit of improving the MTF while reducing both signal and noise aliasing, resulting in an increase of the DQE at high spatial frequencies. For optimal implementation, the converter layer must have very high spatial resolution and the detector must have low readout noise. [ABSTRACT FROM AUTHOR]

The purpose of the current study is to explicate the theoretical structure of online authenticity and to reveal the relationship between the need for popularity and online authenticity. A survey-based research was conducted with 573 randomly selected active users of “Me2day” a popular microblogging service in South Korea. Drawing on a representative sample, we tested the discriminant validity of online authenticity. As predicted, the need for popularity was a significant predictor of online authenticity. Exploratory factor analysis followed by confirmatory factor analysis validated two factors that underlie microblogging users’ online authenticity: (1) sense of real me (SRME); and (2) expression of real me (ERME). Microbloggers with a higher need for popularity had lower SRME and ERME than those with a lower need for popularity. Age and gender were negatively correlated with both need for popularity and online authenticity. Younger microbloggers had a higher need for popularity and lower SRME and ERME than older microbloggers. Male microbloggers had higher need for popularity and lower SRME and ERME than female microbloggers. Theoretical and practical implications for future studies are discussed. [ABSTRACT FROM AUTHOR]

Purpose: The overall goal of this study is to restore kilovoltage computed tomography (kV-CT) images which are disfigured by patients' metal prostheses. By generating a hybrid sinogram that is a combination of kV and megavoltage (MV) projection data, the authors suggest a novel metal artifactreduction (MAR) method that retains the image quality to match that of kV-CT and simultaneously restores the information of metal prostheses lost due to photon starvation. Methods: CT projection data contain information about attenuation coefficients and the total length of the attenuation. By normalizing raw kV projections with their own total lengths of attenuation, mean attenuation projections were obtained. In the same manner, mean density projections of MV-CT were obtained by the normalization of MV projections resulting from the forward projection of density-calibrated MV-CT images with the geometric parameters of the kV-CT device. To generate the hybrid sinogram, metal-affected signals of the kV sinogram were identified and replaced by the corresponding signals of the MV sinogram following a density calibration step with kV data. Filtered backprojection was implemented to reconstruct the hybrid CT image. To validate the authors' approach, they simulated four different scenarios for three heads and one pelvis using metallic rod inserts within a cylindrical phantom. Five inserts describing human body elements were also included in the phantom. The authors compared the image qualities among the kV, MV, and hybrid CT images by measuring the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), the densities of all inserts, and the spatial resolution. In addition, the MAR performance was compared among three existing MAR methods and the authors' hybrid method. Finally, for clinical trials, the authors produced hybrid images of three patients having dental metal prostheses to compare their MAR performances with those of the kV, MV, and three existing MAR methods. Results: The authors compared the image quality and MAR performance of the hybrid method with those of other imaging modalities and the three MAR methods, respectively. The total measured mean of the CNR (SNR) values for the nonmetal inserts was determined to be 14.3 (35.3), 15.3 (37.8), and 25.5 (64.3) for the kV, MV, and hybrid images, respectively, and the spatial resolutions of the hybrid images were similar to those of the kV images. The measured densities of the metal and nonmetal inserts in the hybrid images were in good agreement with their true densities, except in cases of extremely low densities, such as air and lung. Using the hybrid method, major streak artifacts were suitably removed and no secondary artifacts were introduced in the resultant image. In clinical trials, the authors verified that kV and MV projections were successfully combined and turned into the resultant hybrid image with high image contrast, accurate metal information, and few metal artifacts. The hybrid method also outperformed the three existing MAR methods with regard to metal information restoration and secondary artifact prevention. Conclusions: The authors have shown that the hybrid method can restore the overall image quality of kV-CT disfigured by severe metal artifacts and restore the information of metal prostheses lost due to photon starvation. The hybrid images may allow for the improved delineation of structures of interest and accurate dose calculations for radiation treatment planning for patients with metal prostheses. [ABSTRACT FROM AUTHOR]

Abstract: Recently, photon-counting detectors capable of resolving incident x-ray photon energies have been considered for use in spectral x-ray imaging applications. For reliable use of energy-resolved photon-counting detectors (ERPCDs), energy calibration is an essential procedure prior to their use because variations in responses from each pixel of the ERPCD for incident photons, even at the same energy, are inevitable. Energy calibration can be performed using a variety of methods. In all of these methods, the photon spectra with well-defined peak energies are recorded. Every pixel should be calibrated on its own. In this study, we suggest the use of a conventional polychromatic x-ray source (that is typically used in laboratories) for energy calibration. The energy calibration procedure mainly includes the determination of the peak energies in the spectra, flood-field irradiation, determination of peak channels, and determination of calibration curves (i.e., the slopes and intercepts of linear polynomials). We applied a calibration algorithm to a CdTe ERPCD comprised of 128×128pixels with a pitch of 0.35mm using highly attenuated polychromatic x-ray beams to reduce the pulse pile-up effect, and to obtain a narrow-shaped spectrum due to beam hardening. The averaged relative error in calibration curves obtained from 16,384pixels was about 0.56% for 59.6keV photons from an Americium radioisotope. This pixel-by-pixel energy calibration enhanced the signal- and contrast-to-noise ratios in images, respectively, by a factor of ~5 and 3 due to improvement in image homogeneity, compared to those obtained without energy calibration. One secondary finding of this study was that the x-ray photon spectra obtained using a common algorithm for computing x-ray spectra reasonably described the peaks in the measured spectra, which implies easier peak detection without the direct measurement of spectra using a separate spectrometer. The proposed method will be a useful alternative to conventional approaches using radioisotopes, a synchrotron, or specialized x-ray sources (e.g., characteristic or fluorescent x-rays) by reducing concerns over the beam flux, the irradiation field of view, accessibility, and cost. [Copyright &y& Elsevier]

Abstract: We describe a cone-beam computed tomography with insufficient projections obtained from a limited angle scan, the so-called cone-beam digital tomosynthesis. Digital tomosynthesis produces cross-sectional images parallel to the axis of rotation from a series of projection images acquired from a planar detector. The image reconstruction algorithm is based on the cone-beam filtered backprojection method. To suppress the out-of-plane artifacts due to the incomplete sampling over a limited angular range, we applied an apodizing filter in the depth direction. We applied the digital tomosynthesis technique to a multilayer printed circuit board possessing thin slab geometry and evaluated its performance with respect to various operation parameters, such as the total scan angle, the step angle and the number of projection images used for reconstruction. The results showed that the image quality of digital tomosynthesis reconstructed for the total scan angle greater than 60 degrees with a step angle as narrow as possible exhibited that it was comparable to that of the computed tomography. The digital tomosynthesis technique is expected to be practical for extracting internal cross-sectional views, parallel to the scan direction, of objects with thin slab geometry. [Copyright &y& Elsevier]

Purpose: Compressed sensing theory has enabled an accurate, low-dose cone-beam computed tomography (CBCT) reconstruction using a minimal number of noisy projections. However, the reconstruction time remains a significant challenge for practical implementation in the clinic. In this work, we propose a novel gradient projection algorithm, based on the Gradient-Projection-Barzilai-Borwein formulation (GP-BB), that handles the total variation (TV)-norm regularization-based least squares problem for the CBCT reconstruction in a highly efficient manner, with speed acceptable for routine use in the clinic. Methods: CBCT is reconstructed by minimizing an energy function consisting of a data fidelity term and a TV-norm regularization term. Both terms are simultaneously minimized by calculating the gradient projection of the energy function with the step size determined using an approximate Hessian calculation at each iteration, based on the Barzilai-Borwein formulation. To speed up the process, a multiresolution optimization is used. In addition, the entire algorithm was designed to run with a single graphics processing unit (GPU) card. To evaluate the performance, the Shepp-Logan numerical phantom, the CatPhan 600 physical phantom, and a clinically-treated head-and-neck patient were acquired from the TrueBeam™ system (Varian Medical Systems, Palo Alto, CA). For each scan, in total, 364 projections were acquired in a 200° rotation. The imager has 1024 × 768 pixels with 0.388 × 0.388-mm resolution. This was down-sampled to 512 × 384 pixels with 0.776 × 0.776-mm resolution for reconstruction. Evenly spaced angles were subsampled and used for varying the number of projections for the image reconstruction. To assess the performance of our GP-BB algorithm, we have implemented and compared with three compressed sensing-type algorithms, the two of which are popular and published (forward-backward splitting techniques), and the other one with a basic line-search technique. In addition, the conventional Feldkamp-Davis-Kress (FDK) reconstruction of the clinical patient data is compared as well. Results: In comparison with the other compressed sensing-type algorithms, our algorithm showed convergence in ≤30 iterations whereas other published algorithms need at least 50 iterations in order to reconstruct the Shepp-Logan phantom image. With the CatPhan phantom, the GP-BB algorithm achieved a clinically-reasonable image with 40 projections in 12 iterations, in less than 12.6 s. This is at least an order of magnitude faster in reconstruction time compared with the most recent reports utilizing GPU technology given the same input projections. For the head-and-neck clinical scan, clinically-reasonable images were obtained from 120 projections in 34-78 s converging in 12-30 iterations. In this reconstruction range (i.e., 120 projections) the image quality is visually similar to or better than the conventional FDK reconstructed images using 364 projections. This represents a dose reduction of nearly 67% (120/364 projections) while maintaining a reasonable speed in clinical implementation. Conclusions: In this paper, we proposed a novel, fast, low-dose CBCT reconstruction algorithm using the Barzilai-Borwein step-size calculation. A clinically viable head-and-neck image can be obtained within ∼34-78 s while simultaneously cutting the dose by approximately 67%. This makes our GP-BB algorithm potentially useful in an on-line image-guided radiation therapy (IGRT). [ABSTRACT FROM AUTHOR]

Abstract: The performance of a specialized dual γ-ray imager using both mechanical and electronic collimation was evaluated by Monte Carlo simulation (MCNP5). The dual imager consisted of an active collimator and a planar detector that were made from scintillators. The active collimator served not only as a coded aperture for mechanical collimation but also as a first detector for electronic collimation. Therefore, a single system contained both mechanical and electronic collimation. Various types of scintillators were tested and compared with each other in terms of their angular resolution, efficiency, and background noise. In general, a BGO active collimator had the best mechanical collimation performance, and an LaCl3(Ce) active collimator provided the best electronic collimation performance. However, for low radiation energies, the mechanical collimation images made from both scintillators showed the same quality, and, for high radiation energies, electronic collimation images made from both scintillators also show similar quality. Therefore, if mechanical collimation is used to detect low-energy radiation and electronic collimation is applied to reconstruct a high-energy source, either LaCl3(Ce) or BGO would be appropriate for the active collimator of a dual γ-ray imager. These results broaden the choice of scintillators for the active collimator of the dual γ-ray imager, which makes it possible to consider other factors, such as machinability and cost, in making the imager. As a planar detector, BGO showed better performance than other scintillators since its radiation detection efficiency was highest of all. [Copyright &y& Elsevier]

Abstract: Diagnosis and screening of breast cancer using digital mammography, breast tomosynthesis and cone-beam computed tomography are among the most active areas of research in diagnostic radiology. For a better design of imaging systems and the optimization of imaging technologies, numerical phantom studies are essential because of their convenience and the difficulties associated with acquiring clinical data. In this study, we have developed a procedure to numerically generate realistic digital mammograms considering the imaging characteristics of a digital mammography detector, such as resolution and noise. The procedure is composed of the generation of a voxelized breast phantom, projection and image modification. The outer shape of the breast and abnormalities are modeled with geometric functions. Soft tissue is generated by low-pass-filtered white-spectrum noise. Glandular ductal networks are generated by random angles and lengths with some restricted conditions based on anatomical information. A noise-free mammogram with the numerical voxel phantom is achieved by a simple ray-tracing method, and then modified with the known resolution and noise characteristics of an imager. This study will be helpful for the better design of mammography detectors and tomosynthesis algorithms. [Copyright &y& Elsevier]

Abstract: We report the imaging characteristics of the recently developed large-area complementary metal-oxide-semiconductor (CMOS) active-pixel detector for low-energy digital X-ray imaging applications. The detector consists of a scintillator to convert X-ray into light and a photodiode pixel array made by the CMOS fabrication process to convert light into charge signals. Between two layers, we introduce a fiber-optic faceplate (FOP) to avoid direct absorption of X-ray photons in the photodiode array. A single pixel is composed of a photodiode and three transistors, and the pixel pitch is 96μm. The imaging characteristics of the detector have been investigated in terms of modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). From the measured results, the MTF at the Nyquist frequency is about 20% and the DQE around zero-spatial frequency is about 40%. Simple cascaded linear-systems analysis has showed that the FOP prevents direct absorption of X-ray photons within the CMOS photodiode array, leading to a lower NPS and consequently improved DQE especially at high spatial frequencies. [Copyright &y& Elsevier]

Abstract: The application of digital radiography detectors has attracted increasing attention in both medicine and industry. Since the imaging detectors are fabricated by semiconductor manufacturing process over large areas, defective pixels in the detectors are unavoidable. Moreover, the radiation damage due to the routine use of the detectors progressively increases the density of defective pixels. In this study, we present a method of identifying defective pixels in digital radiography detectors based on wavelet analysis. Artifacts generated due to wavelet transformations have been prevented by an additional local threshold method. The proposed method was applied to a sample digital radiography and the result was promising. The proposed method uses a single pair of dark and white images and does not require them to be corrected in gain-and-offset properties. This method will be helpful for the reliable use of digital radiography detectors through the working lifetime. [Copyright &y& Elsevier]

Despite the wind-resistant design performed during the design stage, an existing bridge may still experience severe vortex-induced vibrations (VIVs) because of the installation of new affiliated facilities during its operation period. Therefore, it is necessary to apply control measures to suppress the VIV induced by such changes in configuration. In this study, the VIV performance of a streamlined box girder bridge during the installation of new auxiliary piping system was investigated through a series of sectional model tests and flow visualization tests. Severe vertical VIVs of the bridge used in this study were observed at lower wind speed ranges during wind tunnel tests. Based on the flow pattern around the sectional model, it was inferred that the flow across the deck bottom surface was entirely separated by the new pipelines, which resulted in the periodic generation of shedding vortices in the wake zone and induced deck vibration. Twin downward vertical stabilizer plates (TDVS) were found to be an effective aerodynamic countermeasure for improving the VIV performance of the bridge and could significantly decrease the amplitude of the vertical VIV motion. Additional flow visualization investigations showed that after the TDVS were installed, the vortex shedding in the wake was mitigated, and the location of the vortex shedding was further away from the deck, and hence, considerably suppressed the vertical VIVs. It was found that the effectiveness of the TDVS in improving the aerodynamic performance was significantly dependent on the TDVS parameters, i.e., the plate height and spacing between plate elements. The optimal values of these parameters were correspondingly identified for the bridge deck used in this study after a comprehensive evaluation. • VIV performance of a streamlined box girder bridge installing new pipelines are investigated. • Using twin downwards vertical stabilizer plates (TDVS) as an effective countermeasure to suppress the VIV is proposed. • Optimal parameters of TDVS dimension to suppress the VIV are identified for the bridge deck. • Flow pattern around the deck and the underlying aerodynamic mechanism are investigated by the flow visualization. [ABSTRACT FROM AUTHOR]

This study investigates the imaging performance of a complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) array coupled with a gadolinium oxysulfide phosphor. A wide range of mammographic energy was considered, which corresponds to an aluminum-equivalent thickness in the range of 0.515 to 0.689 mm in terms of half-value layers. The performance metrics include the modulation-transfer function (MTF), Wiener noise-power spectrum (NPS), and detective quantum efficiency (DQE). The detector showed a nonlinear response at low exposure ranges, so it was described using a power-law model to linearize image data before evaluating the MTF, NPS, and DQE. We show that the NPS, which is measured from images without linearization but corrected by the exponent of the power function (viz., nonlinearity correction), can be consistent with that obtained using the linearization procedure. Negligible difference in MTFs measured with and without linearization showed good agreement between the nonlinearity-corrected and linearized DQEs. The DQE performance of the detector was comparable to published data for conventional digital mammography detectors. However, the detector design with a CMOS APS array in conjunction with a thin phosphor was energy-sensitive. The overall spatial-resolution performance (the size of effective aperture) improved by about 13%, the noise performance was degraded by about 22%, and the zero-frequency DQE was reduced by about 26% when measured with a Mo-target beam quality of 25 kV to 31 kV and a similar exposure of about 6 mR. The detector design may be appropriate for operation in a narrow range of energy. Further design considerations of the phosphor with output that tolerates variations in energy could lead to applications in convertible mammography and tomosynthesis. • Power model for nonlinear detector responses describes NPS without linearization. • Detector design with CMOS APS/thin gadolinium oxysulfide phosphor is energy-sensitive. • Lower optical Swank factor limits the performance of gadolinium oxysulfide phosphors. [ABSTRACT FROM AUTHOR]

To enhance sustainability and resilience against climate change in infrastructure, a quantitative evaluation of both environmental impact and cost is important within a life cycle framework. Climate change effects can lead performance deterioration in bridge components during their operational phase, highlighting the necessity for a risk-based evaluation process aligned with maintenance strategies. This study employs a two-phase life cycle assessments (LCA) framework. First, risk assessments are conducted to evaluate the impact of climate change on steel plate girder bridges and prestressed concrete (PSC) girder bridges under identical structural conditions. The reduction in flexural strength of steel plate girders and PSC girders due to changes in environmental variables such as temperature and relative humidity, induced by various climate change scenarios, was evaluated analytically. Subsequently, life cycle environmental impact and cost assessments were performed, including maintenance outcomes derived from risk assessments. The findings revealed that the environmental impact and cost could increase by approximately 12.4% when climate change is considered, compared to scenarios where it is not taken into account. Sensitivity analyses were performed to identify the key factors influencing environmental impact and cost. The analysis determined that the frequency of preventive maintenance, the recycling rate, and environmental cost coefficient weight in the life cycle assessment significantly affected the results., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

The feasibility of single-exposure dual-energy imaging (DEI) was investigated in pursuit of motion-artifact-free subtraction angiography. To acquire low- and high-energy images simultaneously from a single X-ray exposure, a sandwich-like multilayered detector was fabricated by configuring two phosphor-coupled photodiode array layers in tandem. A simple analytic model describing the signal in DE-reconstructed images was derived. For the feasibility test, two plastic phantoms with linear arrays of cylindrical holes were prepared to contain iodinated water. One consisted of the same-diameter cylinders with different iodine concentrations, whereas the other had the different-diameter cylinders with the same iodine concentration. The concentration and size discrimination capabilities of single-exposure DEI were evaluated by investigating the phantom images. While the image noise relative to the signal was almost independent of the mass thickness of iodine, the iodine detectability improved with the mass thickness. The detectability performance at a lower tube voltage (e.g. 60 kV) outperformed those at higher voltages, as expected from the model. The results obtained in this study demonstrate the potential applicability of the single-exposure approach to motion-artifact-free subtraction angiography., (Copyright © 2022 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.)

For the purpose of real-time scan-protocol optimisation and patient-specific dose management in cone-beam computed tomography, we introduce a numerical algorithm that estimates the primary dose distributions in reconstructed images. The proposed algorithm is based on the ray-tracing technique and utilises reconstructed voxel data and scanning protocol. The algorithm is validated with the Monte Carlo (MC) and conventional model-based dose reconstruction methods for the simple cylindrical water and anthropomorphic head phantoms. The algorithm shows good agreement with both methods in terms of the zeroth-order x-ray interactions, which exclude the higher-order x-ray interactions at sites distant from the first interactions, and it consumes a significantly lower computational cost compared with the MC method. The differences between the proposed algorithm and the model-based dose reconstruction method as well as the improvement strategies of the algorithm are discussed in detail., (© The Author(s) 2021. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Purpose: Dedicated breast CT is an emerging volumetric X-ray imaging modality for diagnosis that does not require any painful breast compression. To improve the detection rate of weakly enhanced lesions, an adaptive image rescaling (AIR) technique was proposed., Materials and Methods: Two disks containing five identical holes and five holes of different diameters were scanned using 60/100 kVp to obtain single-energy CT (SECT), dual-energy CT (DECT), and AIR images. A piece of pork was also scanned as a subclinical trial. The image quality was evaluated using image contrast and contrast-to-noise ratio (CNR). The difference of imaging performances was confirmed using student's t test., Results: Total mean image contrast of AIR (0.70) reached 74.5% of that of DECT (0.94) and was higher than that of SECT (0.22) by 318.2%. Total mean CNR of AIR (5.08) was 35.5% of that of SECT (14.30) and was higher than that of DECT (2.28) by 222.8%. A similar trend was observed in the subclinical study., Conclusion: The results demonstrated superior image contrast of AIR over SECT, and its higher overall image quality compared to DECT with half the exposure. Therefore, AIR seems to have the potential to improve the detectability of lesions with dedicated breast CT., Competing Interests: Conflicts of Interest: The authors have no potential conflicts of interest to disclose., (Copyrights © 2021 The Korean Society of Radiology.)

Goal: We investigate the signal and noise performance of an x-ray microtomography system that incorporates a complementary metal-oxide-semiconductor flat-panel detector as a projection image receptor., Methods: Signal and noise performance is analyzed in the Fourier domain using modulation-transfer function (MTF), noise-power spectrum (NPS), and noise-equivalent number of quanta (NEQ) with respect to magnification and different convolution kernels for image reconstruction., Results: Higher magnification provides lower NPS, and thus, higher NEQ performance in the transaxial planes from microtomography. A window function capable of smoothing the ramp filter edge to below one-half of the Nyquist limit results in better performance in terms of NPS and NEQ. The characteristics of convolution kernels do not affect signal and noise performance in longitudinal planes; hence, MTF performance mainly dominates the NEQ performance. The signal and noise performances investigated in this study are demonstrated with images obtained from the contrast phantom and postmortem mouse., Conclusion: The results of our study could be helpful in developing x-ray microtomography systems based on flat-panel detectors.

X-ray computed laminography is widely used in nondestructive testing of relatively flat objects using an oblique scanning configuration for data acquisition. In this work, a new scanning scheme is proposed in conjunction with the compressive-sensing-based image reconstruction for reducing imaging radiation dose and scanning time. We performed a numerical study comparing image qualities acquired by various scanning configurations that are practically implementable: single-arc, double-arc, oblique, and spherical-sinusoidal trajectories. A compressive-sensing-inspired total-variation (TV) minimization algorithm was used to reconstruct the images from the data acquired at only 40 projection views in those trajectories. It was successfully demonstrated that the proposed scanning scheme outperforms the others in terms of image contrast and spatial resolution, although the oblique scanning scheme showed a comparable resolution property. We believe that the proposed scanning method may provide a solution to fast and low-dose nondestructive testing of radiation-sensitive and highly integrated devices such as multilayer microelectronic circuit boards.

A bioassay-guided fractionation and chemical investigation of the MeOH extract from the twigs of Lindera glauca (SIEB. et ZUCC.) BLUME resulted in the isolation and identification of six lignans (1-6) including three new lignan derivatives, named linderuca A (1), B (2), and C (3). The structures of the new compounds (1-3) were determined on the basis of spectroscopic analyses, including two dimensional NMR and circular dichroism (CD) spectroscopy studies. The cytotoxic activities of the isolates (1-6) were evaluated by determining their inhibitory effects on human tumor cell lines. Compounds 1-5 showed antiproliferative activities against A549, SK-OV-3, SK-MEL-2, and HCT-15 cell lines with IC50 values of 7.79-29.42 µM. Based on the understanding that inflammation is a crucial cause of tumor progression, we also investigated the anti-inflammatory activities of the isolates (1-6) in the lipopolysaccharide-stimulated murine microglia BV-2 cell line by measuring nitric oxide (NO) levels. The new lignans (1-3) significantly inhibited NO production with IC50 values of 12.10, 9.48, and 9.87 µM, respectively, without cytotoxicity.

The absorbed energy distribution (AED) in X-ray imaging detectors is an important factor that affects both energy resolution and image quality through the Swank factor and detective quantum efficiency. In the diagnostic energy range (20-140 keV), escape of characteristic photons following photoelectric absorption and Compton scatter photons are primary sources of absorbed-energy dispersion in X-ray detectors. In this paper, we describe the development of an analytic model of the AED in compound X-ray detector materials, based on the cascaded-systems approach, that includes the effects of escape and reabsorption of characteristic and Compton-scatter photons. We derive analytic expressions for both semi-infinite slab and pixel geometries and validate our approach by Monte Carlo simulations. The analytic model provides the energy-dependent X-ray response function of arbitrary compound materials without time-consuming Monte Carlo simulations. We believe this model will be useful for correcting spectral distortion artifacts commonly observed in photon-counting applications and optimal design and development of novel X-ray detectors.

Purpose: This study investigates the fundamental signal and noise performance limitations imposed by the stochastic nature of x-ray interactions in selected photoconductor materials, such as Si, a-Se, CdZnTe, HgI(2), PbI(2), PbO, and TlBr, for x-ray spectra typically used in mammography., Methods: It is shown how Monte Carlo simulations can be combined with a cascaded model to determine the absorbed energy distribution for each combination of photoconductor and x-ray spectrum. The model is used to determine the quantum efficiency, mean energy absorption per interaction, Swank noise factor, secondary quantum noise, and zero-frequency detective quantum efficiency (DQE)., Results: The quantum efficiency of materials with higher atomic number and density demonstrates a larger dependence on convertor thickness than those with lower atomic number and density with the exception of a-Se. The mean deposited energy increases with increasing average energy of the incident x-ray spectrum. HgI(2), PbI(2), and CdZnTe demonstrate the largest increase in deposited energy with increasing mass loading and a-Se and Si the smallest. The best DQE performances are achieved with PbO and TlBr. For mass loading greater than 100 mg cm(-2), a-Se, HgI(2), and PbI(2) provide similar DQE values to PbO and TlBr., Conclusions: The quantum absorption efficiency, average deposited energy per interacting x-ray, Swank noise factor, and detective quantum efficiency are tabulated by means of graphs which may help with the design and selection of materials for photoconductor-based mammography detectors. Neglecting the electrical characteristics of photoconductor materials and taking into account only x-ray interactions, it is concluded that PbO shows the strongest signal-to-noise ratio performance of the materials investigated in this study.

The purpose of this work is to demonstrate an ultra-fast reconstruction technique for digital tomosynthesis (DTS) imaging based on the algorithm proposed by Feldkamp, Davis, and Kress (FDK) using standard general-purpose graphics processing unit (GPGPU) programming interface. To this end, the FDK-based DTS algorithm was programmed "in-house" with C language with utilization of 1) GPU and 2) central processing unit (CPU) cards. The GPU card consisted of 480 processing cores (2 x 240 dual chip) with 1,242 MHz processing clock speed and 1,792 MB memory space. In terms of CPU hardware, we used 2.68 GHz clock speed, 12.0 GB DDR3 RAM, on a 64-bit OS. The performance of proposed algorithm was tested on twenty-five patient cases (5 lung, 5 liver, 10 prostate, and 5 head-and-neck) scanned either with a full-fan or half-fan mode on our cone-beam computed tomography (CBCT) system. For the full-fan scans, the projections from 157.5°-202.5° (45°-scan) were used to reconstruct coronal DTS slices, whereas for the half-fan scans, the projections from both 157.5°-202.5° and 337.5°-22.5° (2 x 45°-scan) were used to reconstruct larger FOV coronal DTS slices. For this study, we chose 45°-scan angle that contained ~80 projections for the full-fan and ~160 projections with 2 x 45°-scan angle for the half-fan mode, each with 1024 x 768 pixels with 32-bit precision. Absolute pixel value differences, profiles, and contrast-to-noise ratio (CNR) calculations were performed to compare and evaluate the images reconstructed using GPU- and CPU-based implementations. The time dependence on the reconstruction volume was also tested with (512 x 512) x 16, 32, 64, 128, and 256 slices. In the end, the GPU-based implementation achieved, at most, 1.3 and 2.5 seconds to complete full reconstruction of 512 x 512 x 256 volume, for the full-fan and half-fan modes, respectively. In turn, this meant that our implementation can process > 13 projections-per-second (pps) and > 18 pps for the full-fan and half-fan modes, respectively. Since commercial CBCT system nominally acquires 11 pps (with 1 gantry-revolution-per-minute), our GPU-based implementation is sufficient to handle the incoming projections data as they are acquired and reconstruct the entire volume immediately after completing the scan. In addition, on increasing the number of slices (hence volume) to be reconstructed from 16 to 256, only minimal increases in reconstruction time were observed for the GPU-based implementation where from 0.73 to 1.27 seconds and 1.42 to 2.47 seconds increase were observed for the full-fan and half-fan modes, respectively. This resulted in speed improvement of up to 87 times compared with the CPU-based implementation (for 256 slices case), with visually identical images and small pixel-value discrepancies (< 6.3%), and CNR differences (< 2.3%). With this achievement, we have shown that time allocation for DTS image reconstruction is virtually eliminated and that clinical implementation of this approach has become quite appealing. In addition, with the speed achievement, further image processing and real-time applications that was prohibited prior due to time restrictions can now be tempered with.

Purpose: Energy-resolved x-ray imaging has the potential to improve contrast-to-noise ratio by measuring the energy of each interacting photon and applying optimal weighting factors. The success of energy-resolving photon-counting (EPC) detectors relies on the ability of an x-ray detector to accurately measure the energy of each interacting photon. However, the escape of characteristic emissions and Compton scatter degrades spectral information. This article makes the theoretical connection between accuracy and imprecision in energy measurements with the x-ray Swank factor for a-Se, Si, CdZnTe, and HgI2-based detectors., Methods: For a detector that implements adaptive binning to sum all elements in which x-ray energy is deposited for a single interaction, energy imprecision is shown to depend on the Swank factor for a large element with x rays incident at the center. The response function for each converter material is determined using Monte Carlo methods and used to determine energy accuracy, Swank factor, and relative energy imprecision in photon-energy measurements., Results: For each material, at energies below the respective K edges, accuracy is close to unity and imprecision is only a few percent. Above the K-edge energies, characteristic emission results in a drop in accuracy and precision that depends on escape probability. In Si, and to some extent a-Se, Compton-scatter escape also degrades energy precision with increasing energy. The influence of converter thickness on energy accuracy and imprecision is modest for low-Z materials but becomes important when using high-Z materials at energies greater than the K-edge energies., Conclusions: Accuracy and precision in energy measurements by EPC detectors are determined largely by the energy-dependent x-ray Swank factor. Modest decreases in the Swank factor (5%-15%) result in large increases in relative imprecision (30%-40%).