Search

The measured spatial resolution of augmented reality head‐mounted displays (AR HMDs) is determined by three components: optics, display, and the rendering pipeline, which includes the anti‐aliasing method. Therefore, separating and quantifying the contributions from these components is necessary for evaluating the spatial resolution of AR HMDs. We demonstrate a method for quantifying the contributions from the optical performance and the rendering pipeline on the spatial resolution of AR HMD using point‐spread function (PSF) analysis. In this method, an imaging photometer captures a series of rendered scenes on the AR HMD that consist of arrays of spheres of increasing sizes with different anti‐aliasing (AA) methods. The contributions from the optics, display, and anti‐aliasing methods can be separated, and we find that temporal anti‐aliasing (TAA) and multisample anti‐aliasing (MSAA) are in good agreement with the performance of no AA. However, fast approximate anti‐aliasing (FXAA) results in decreased luminance for smaller rendered targets and a different spatial resolution for larger targets. Finally, we repeated our methods on multiple HMDs and characterized the dependence of the spatial resolution across the field of view. These measurements show significant non‐uniformity in the optical contribution to the spatial resolution. [ABSTRACT FROM AUTHOR]

We demonstrate a point spread function method for measuring the angular dependence of the spatial resolution of a virtual reality head mounted display. The angular dependence of spatial resolution of the imaging detector was characterized to remove the detector's contribution at each angular location measured on the VR HMD. This method allows measuring the twodimensional spatial resolution and modulation transfer function. [ABSTRACT FROM AUTHOR]

We evaluate the geometric distortion on video see‐through (VST) head‐mounted displays (HMDs) with single‐camera and dualcamera design. We present the experimental setup and metrology for geometric calibration and VST geometric distortion measurement. Physical geometric distortion is compared to the distortion of digital content on a VST HMD. We investigate the impacts of camera misalignment and depth distance on VST geometric distortion with angular‐based distortion correction. [ABSTRACT FROM AUTHOR]

Video see‐through (VST) head‐mounted displays (HMDs) reconstruct the physical world using outward‐facing cameras and depth sensors. One of the major challenges for VST HMDs is the geometric distortion of the physical pass‐through content. In this study, we present the experimental setup and metrology for VST geometric distortion measurement on single‐camera and dual‐camera VST HMDs. The VST geometric distortion is compared to the digital distortion by the HMD. Finally, we investigate the impacts of camera misalignment and depth distance on VST geometric distortion without and with angular‐based distortion correction. The results demonstrate that camera misalignment with respect to the eye position is the primary root cause for the distortion. Dual‐camera setup is necessary to minimize the VST geometric distortion by placing the cameras close to the eye positions. Although distortion correction can partially mitigate VST geometric distortion in a 2D plane, it remains a challenge for VST distortion correction at multiple depth distance in the 3D space. The method and findings presented of this study may provide guidelines for evaluation of spatial accuracy on VST HMDs and hardware design. [ABSTRACT FROM AUTHOR]

Spatially dependent veiling glare in medical extended reality (MXR) degrades image quality and needs to be characterized across technologies. Measurement methods of veiling glare on virtual and augmented reality (VR and AR) head-mounted displays (HMDs) have not been established in regulatory evaluation of MXR devices or display measurement standards. We describe an experimental bench setup enabling highly flexible translations and rotations of the light measuring device in five degrees of freedom within the eye box. Glare point spread functions (PSFs) of multiple VR and AR headsets are extracted and compared across the display field of view (FOV) in dark environment. At the center, the evaluated VR headsets (HTC VIVE Pro and VIVE Pro 2) demonstrate reduced long-range glare compared to the tested AR HMDs (Microsoft HoloLens 2 and Epson Moverio BT-300). The measured PSFs at multiple locations are spatially invariant for the HoloLens 2. However, veiling glare on the evaluated VR HMDs substantially increases toward the periphery of the FOV primarily due to optical aberration. For VR devices in medical use, increased peripheral glare can lead to image quality degradation and poor visualization of anatomical details. [ABSTRACT FROM AUTHOR]

The molecular chaperone GroEL of C. sakazakii, a highly conserved protein encoded by the gene grol, has the basic function of responding to heat shock, thus enhancing the bacterium's adaptation to dry and high-temperature environments, which poses a threat to food safety and human health. Our previous study demonstrated that GroEL was found in the bacterial membrane fraction and caused a strong immune response in C. sakazakii. In this study, we tried to elucidate the subcellular location and virulent effects of GroEL. In live C. sakazakii cells, GroEL existed in both the soluble and insoluble fractions. To study the secretory mechanism of GroEL protein, a non-reduced Western immunoblot was used to analyze the form of the protein, and the result showed that the exported GroEL protein was mainly in monomeric form. The exported GroEL could also be located on bacterial surface. To further research the virulent effect of C. sakazakii GroEL, an indirect immunofluorescence assay was used to detect the adhesion of recombinant GroEL protein to HCT-8 cells. The results indicated that the recombinant GroEL protein could adhere to HCT-8 cells in a short period of time. The recombinant GroEL protein could activate the NF-κB signaling pathway to release more pro-inflammatory cytokines (TNF-α, IL-6 and IL-8), downregulating the expression of tight-junction proteins (claudin-1, occluding, ZO-1 and ZO-2), which collectively resulted in dose-dependent virulent effects on host cells. Inhibition of the grol gene expression resulted in a significant decrease in bacterial adhesion to and invasion of HCT-8 cells. Moreover, the deficient GroEL also caused slow growth, decreased biofilm formation, defective motility and abnormal filamentation of the bacteria. In brief, C. sakazakii GroEL was an important virulence factor. This protein was not only crucial for the physiological activity of C. sakazakii but could also be secreted to enhance the bacterium's adhesion and invasion capabilities. [ABSTRACT FROM AUTHOR]

Cronobacter sakazakii is an opportunistic Gram-negative pathogen that has been identified as a causative agent of severe foodborne infections with a higher risk of mortality in neonates, premature infants, the elderly, and immunocompromised populations. The specific pathogenesis mechanisms of C. sakazakii, such as adhesion and colonization, remain unclear. Previously, we conducted comparative proteomic studies on the two strains with the stronger and weaker infection ability, respectively, and found an interesting protein, ESA_00986, which was more highly expressed in the strain with the stronger ability. This unknown protein, predicted to be a type of invasitin related to invasion, may be a critical factor contributing to its virulence. This study aimed to elucidate the precise roles of the ESA_00986 gene in C. sakazakii by generating gene knockout mutants and complementary strains. The mutant and complementary strains were assessed for their biofilm formation, mobility, cell adhesion and invasion, and virulence in a rat model. Compared with the wild-type strain, the mutant strain exhibited a decrease in motility, whereas the complementary strain showed comparable motility to the wild-type. The biofilm-forming ability of the mutant was weakened, and the mutant also exhibited attenuated adhesion to/invasion of intestinal epithelial cells (HCT-8, HICE-6) and virulence in a rat model. This indicated that ESA_00986 plays a positive role in adhesion/invasion and virulence. This study proves that the ESA_00986 gene encodes a novel virulence factor and advances our understanding of the pathogenic mechanism of C. sakazakii. [ABSTRACT FROM AUTHOR]

Monocular image quality on virtual reality (VR) head‐mounted displays (HMDs) is radially variant on each eye piece. The virtual image is blurred at the periphery of display field of view primarily by thin lenses stacked on top of the VR display backplane, resulting in image resolution and contrast degradation. Conventional measurement methods adopted from flat‐panel display evaluation do not consider the spatially variant image artifacts by the additional optical components, and thus may not be adequate to assess the image quality in VR. We develop novel test patterns and a new method to measure the radially variant Michelson contrast on VR HMDs. The new method demonstrates efficient VR image quality evaluation using varied interpupillary distance settings. [ABSTRACT FROM AUTHOR]

We demonstrate a point‐spread function (PSF) method for measuring the spatial resolution of augmented reality head mounted displays (AR HMD). Spatial resolution of HMDs is determined by optical and display performance and our method allows for separating these contributions to spatial resolution. Calculations illustrate the dependence of the HMD's PSF on the relative size and symmetry of the display pixels and optical PSF as a function of the size of target displayed. We tested our method on the Microscoft HoloLens 2 and show that the ratio of the optics to display PSF widths is 0.76. [ABSTRACT FROM AUTHOR]

Virtual reality (VR) head mounted displays (HMDs) require both high spatial resolution and fast temporal response. However, methods to quantify the VR image quality in the spatiotemporal domain when motion exists are not yet standardized. In this study, we characterize the spatiotemporal capabilities of three VR devices: the HTC VIVE, VIVE Pro, and VIVE Pro 2 during smooth pursuit. A spatiotemporal model for VR HMDs is presented using measured spatial and temporal characteristics. Among the three evaluated headsets, the VIVE Pro 2 improves the display temporal performance using a fast 120 Hz refresh rate and pulsed emission with a small duty cycle of 5%. In combination with a high pixel resolution beyond 2 k × 2 k per eye, the VIVE Pro 2 achieves an improved spatiotemporal performance compared to the VIVE and VIVE Pro in the high spatial frequency range above 8 cycles per degree during smooth pursuit. The result demonstrates that reducing the display emission duty cycle to less than 20% is beneficial to mitigate motion blur in VR HMDs. Frame rate reduction (e.g., to below 60 Hz) of the input signal compared to the display refresh rate of 120 Hz yields replicated shadow images that can affect the image quality under motion. This work supports the regulatory science research efforts in development of testing methods to characterize the spatiotemporal performance of VR devices for medical use. [ABSTRACT FROM AUTHOR]

We characterized augmented reality (AR) displays and developed a computational task‐based model to evaluate their image quality. The model enables fast assessment of image quality and evaluation of tradeoffs between display configurations such as display luminance response, uniformity, resolution, and noise. This work supports the development and optimization of AR displays without extensive measurements or resource‐intensive perception studies. [ABSTRACT FROM AUTHOR]

Purpose: We investigate the feasibility of slot‐scan dual‐energy (DE) bone densitometry on motorized radiographic equipment. This approach will enable fast quantitative measurements of areal bone mineral density (aBMD) for opportunistic evaluation of osteoporosis. Methods: We investigated DE slot‐scan protocols to obtain aBMD measurements at the lumbar spine (L‐spine) and hip using a motorized x‐ray platform capable of synchronized translation of the x‐ray source and flat‐panel detector (FPD). The slot dimension was 5 × 20 cm2. The DE slot views were processed as follows: (1) convolution kernel‐based scatter correction, (2) unfiltered backprojection to tile the slots into long‐length radiographs, and (3) projection‐domain DE decomposition, consisting of an initial adipose–water decomposition in a bone‐free region followed by water–CaHA decomposition with adjustment for adipose content. The accuracy and reproducibility of slot‐scan aBMD measurements were investigated using a high‐fidelity simulator of a robotic x‐ray system (Siemens Multitom Rax) in a total of 48 body phantom realizations: four average bone density settings (cortical bone mass fraction: 10–40%), four body sizes (waist circumference, WC = 70–106 cm), and three lateral shifts of the body within the slot field of view (FOV) (centered and ±1 cm off‐center). Experimental validations included: (1) x‐ray test‐bench feasibility study of adipose–water decomposition and (2) initial demonstration of slot‐scan DE bone densitometry on the robotic x‐ray system using the European Spine Phantom (ESP) with added attenuation (polymethyl methacrylate [PMMA] slabs) ranging 2 to 6 cm thick. Results: For the L‐spine, the mean aBMD error across all WC settings ranged from 0.08 g/cm2 for phantoms with average cortical bone fraction wcortical = 10% to ∼0.01 g/cm2 for phantoms with wcortical = 40%. The L‐spine aBMD measurements were fairly robust to changes in body size and positioning, e.g., coefficient of variation (CV) for L1 with wcortical = 30% was ∼0.034 for various WC and ∼0.02 for an obese patient (WC = 106 cm) changing lateral shift. For the hip, the mean aBMD error across all phantom configurations was about 0.07 g/cm2 for a centered patient. The reproducibility of hip aBMD was slightly worse than in the L‐spine (e.g., in the femoral neck, the CV with respect to changing WC was ∼0.13 for phantom realizations with wcortical = 30%) due to more challenging scatter estimation in the presence of an air–tissue interface within the slot FOV. The aBMD of the hip was therefore sensitive to lateral positioning of the patient, especially for obese patients: e.g., the CV with respect to patient lateral shift for femoral neck with WC = 106 cm and wcortical = 30% was 0.14. Empirical evaluations confirmed substantial reduction in aBMD errors with the proposed adipose estimation procedure and demonstrated robust aBMD measurements on the robotic x‐ray system, with aBMD errors of ∼0.1 g/cm2 across all three simulated ESP vertebrae and all added PMMA attenuator settings. Conclusions: We demonstrated that accurate aBMD measurements can be obtained on a motorized FPD‐based x‐ray system using DE slot‐scans with kernel‐based scatter correction, backprojection‐based slot view tiling, and DE decomposition with adipose correction. [ABSTRACT FROM AUTHOR]

Purpose: The recently introduced robotic x‐ray systems provide the flexibility to acquire cone‐beam computed tomography (CBCT) data using customized, application‐specific source‐detector trajectories. We exploit this capability to mitigate the effects of x‐ray scatter and noise in CBCT imaging of weight‐bearing foot and cervical spine (C‐spine) using scan orbits with a tilted rotation axis. Methods: We used an advanced CBCT simulator implementing accurate models of x‐ray scatter, primary attenuation, and noise to investigate the effects of the orbital tilt angle in upright foot and C‐spine imaging. The system model was parameterized using a laboratory version of a three‐dimensional (3D) robotic x‐ray system (Multitom RAX, Siemens Healthineers). We considered a generalized tilted axis scan configuration, where the detector remained parallel to patient's long body axis during the acquisition, but the elevation of source and detector was changing. A modified Feldkamp–Davis–Kress (FDK) algorithm was developed for reconstruction in this configuration, which departs from the FDK assumption of a detector that is perpendicular to the scan plane. The simulated foot scans involved source‐detector distance (SDD) of 1386 mm, orbital tilt angles ranging 10° to 40°, and 400 views at 1 mAs/view and 0.5° increment; the C‐spine scans involved −25° to −45° tilt angles, SDD of 1090 mm, and 202 views at 1.3 mAs and 1° increment The imaging performance was assessed by projection‐domain measurements of the scatter‐to‐primary ratio (SPR) and by reconstruction‐domain measurements of contrast, noise and generalized contrast‐to‐noise ratio (gCNR, accounting for both image noise and background nonuniformity) of the metatarsals (foot imaging) and cervical vertebrae (spine imaging). The effects of scatter correction were also compared for horizontal and tilted scans using an ideal Monte Carlo (MC)‐based scatter correction and a frame‐by‐frame mean scatter correction. Results: The proposed modified FDK, involving projection resampling, mitigated streak artifacts caused by the misalignment between the filtering direction and the detector rows. For foot imaging (no grids), an optimized 20° tilted orbit reduced the maximum SPR from ~1.5 in a horizontal scan to <0.5. The gCNR of the second metatarsal was enhanced twofold compared to a horizontal orbit. For the C‐spine (with vertical grids), imaging with a tilted orbit avoided highly attenuating x‐ray paths through the lower cervical vertebrae and shoulders. A −35° tilted orbit yielded improved image quality and visualization of the lower cervical spine: the SPR of lower cervical vertebrae was reduced from ~10 (horizontal orbit) to <6 (tilted orbit), and the gCNR for C5–C7 increased by a factor of 2. Furthermore, tilted orbits showed potential benefits over horizontal orbits by enabling scatter correction with a simple frame‐by‐frame mean correction without substantial increase in noise‐induced artifacts after the correction. Conclusions: Tilted scan trajectories, enabled by the emerging robotic x‐ray system technology, were optimized for CBCT imaging of foot and cervical spine using an advanced simulation framework. The results demonstrated the potential advantages of tilted axis orbits in mitigation of scatter artifacts and improving contrast‐to‐noise ratio in CBCT reconstructions. [ABSTRACT FROM AUTHOR]

Medical imaging systems like full field digital mammography (FFDM) and digital breast tomosynthesis (DBT) commonly use amorphous selenium (a-Se) based passive pixel sensor (PPS) direct conversion x-ray detectors. On one hand, direct conversion detectors inherently offer better resolution characteristics in terms of a higher modulation transfer function (MTF), in comparison to the indirect CsI:Tl PPS x-ray imager. On the other hand, especially at lower doses, this superior performance of the direct imager is seldom retained in its detective quantum efficiency (DQE) curves. It is well known that a-Se PPS x-ray imagers suffer from high additive electronic noise originating from the from the amorphous silicon (a-Si) thin film transistor (TFT) array that is being used in the current back-plane technology. This degrades the noise power spectrum (NPS) and subsequently the overall DQE. To address this deficiency, we propose to replace the PPS back-plane by active pixel sensor (APS) back-plane technology, which has the potential to reduce the back-plane electronic noise by amplifying the input signal, especially at low doses. The proposed APS is based on amorphous In–Ga–Zn–O (a-IGZO) TFT technology, which can offer high mobility (5–20 cm2 V−1 s−1), low leakage current (<10−13 A) and low flicker noise (Hooge's parameter αH ~ 1.5 10−3), leading to better imager noise performance. To test our hypothesis, we used linear cascaded systems analysis to model the imaging performance (MTF, NPS and DQE) of the PPS and APS a-Se direct imagers. This model was first validated using experimentally measured data obtained for a 85 µm pixel pitch a-Se/a-Si TFT PPS imager. Using this model, we analyzed the noise performance of the direct a-Se and indirect CsI:Tl x-ray a-IGZO APS imagers at different dose and electronic noise levels. Obtained results clearly showed that lowering back-plane electronic noise can significantly improve the performance of the a-Se/a-IGZO TFT APS imager. Our simulated results showed that a higher DQE at lower radiation doses (maximum DQE of 0.6 can be achieved at an exposure level of 1 µGy) can be achieved with the a-Se detector, thereby making this combination a promising candidate for low dose applications like DBT. [ABSTRACT FROM AUTHOR]

High-resolution, low-noise X-ray detectors based on CMOS active pixel sensor (APS) technology have demonstrated superior imaging performance for digital breast tomosynthesis (DBT). This paper presents a task-based model for a high-resolution medical imaging system to evaluate its ability to detect simulated microcalcifications and masses as lesions for breast cancer. A 3-D cascaded system analysis for a 50- \mu \textm pixel pitch CMOS APS X-ray detector was integrated with an object task function, a medical imaging display model, and the human eye contrast sensitivity function to calculate the detectability index and area under the ROC curve (AUC). It was demonstrated that the display pixel pitch and zoom factor should be optimized to improve the AUC for detecting small microcalcifications. In addition, detector electronic noise of smaller than 300 e− and a high display maximum luminance (>1000 cd/cm ^2) are desirable to distinguish microcalcifications of 150~\mu \textm in size. For low contrast mass detection, a medical imaging display with a minimum of 12-bit gray levels is recommended to realize accurate luminance levels. A wide projection angle range of greater than ±30° in combination with the image gray level magnification could improve the mass detectability especially when the anatomical background noise is high. On the other hand, a narrower projection angle range below ±20° can improve the small, high contrast object detection. Due to the low mass contrast and luminance, the ambient luminance should be controlled below 5 cd/ \textm^2 . Task-based modeling provides important firsthand imaging performance of the high-resolution CMOS-based medical imaging system that is still at early stage development for DBT. The modeling results could guide the prototype design and clinical studies in the future. [ABSTRACT FROM AUTHOR]

An amorphous indium–tin–zinc-oxide thin-film transistor (a-ITZO TFT)-based voltage-mode active pixel sensor (V-APS) is discussed, for the first time, in this paper. The a-ITZO TFT shows superior electrical characteristics, including a high field-effect mobility ( \mu \mathrm {\mathbf {EFF}} > 30 cm2/ \text V\cdot \text s ), a steep subthreshold slope (SS < 200 mV/decade), and a low OFF-current ( I\mathrm{\scriptscriptstyle OFF} < 10^{-14} A), that are suitable for applications such as X-ray imagers. The proposed V-APS is based on the top-illuminated organic photodiode (OPD) or amorphous silicon p+-i-n+ photodiode (a-Si p+-i-n+ PD). Simulation results indicate that, in contrast with common source V-APS, source follower (SF) V-APS is more desirable for X-ray imagers due to its better linearity property. The OPD or the a-Si p+-i-n+ PD does not affect the voltage gain of SF V-APS. But the PDs have different influences on charge-to-voltage conversion gain. The impact of PD capacitances and dark saturation currents on detectable quantities of electrons is also investigated. The influence of the TFT threshold voltage shift on circuit performance, sensitivity, and noise analysis of SF V-APS is discussed. [ABSTRACT FROM PUBLISHER]

Purpose: The breast cancer detection rate for digital breast tomosynthesis (DBT) is limited by the xray image quality. The limiting Nyquist frequency for current DBT systems is around 5 lp/mm, while the fine image details contained in the high spatial frequency region (>5 lp/mm) are lost. Also today the tomosynthesis patient dose is high (0.67-3.52 mGy). To address current issues, in this paper, for the first time, a high-resolution low-dose organic photodetector/amorphous In-Ga-Zn-O thin-film transistor (a-IGZO TFT) active pixel sensor (APS) x-ray imager is proposed for next generation DBT systems. Methods: The indirect x-ray detector is based on a combination of a novel low-cost organic photodiode (OPD) and a cesium iodide-based (CsI:Tl) scintillator. The proposed APS x-ray imager overcomes the difficulty of weak signal detection, when small pixel size and low exposure conditions are used, by an on-pixel signal amplification with a significant charge gain. The electrical performance of a-IGZO TFT APS pixel circuit is investigated by SPICE simulation using modified Rensselaer Polytechnic Institute amorphous silicon (a-Si:H) TFT model. Finally, the noise, detective quantum efficiency (DQE), and resolvability of the complete system are modeled using the cascaded system formalism. Results: The result demonstrates that a large charge gain of 31-122 is achieved for the proposed high-mobility (5-20 cm²/Vs) amorphous metal-oxide TFT APS. The charge gain is sufficient to eliminate the TFT thermal noise, flicker noise as well as the external readout circuit noise. Moreover, the low TFT (<10-13 A) and OPD (<10-8 A/cm²) leakage currents can further reduce the APS noise. Cascaded system analysis shows that the proposed APS imager with a 75 µm pixel pitch can effectively resolve the Nyquist frequency of 6.67 lp/mm, which can be further improved to ~101p/mm if the pixel pitch is reduced to 50µm. Moreover, the detector entrance exposure per projection can be reduced from 1 to 0.3 mR without a significant reduction of DQE. The signal-to-noise ratio of the a-IGZO APS imager under 0.3 mR x-ray exposure is comparable to that of a-Si:H passive pixel sensor imager under 1 mR, indicating good image quality under low dose. A threefold reduction of current tomosynthesis dose is expected if proposed technology is combined with an advanced DBT image reconstruction method. Conclusions: The proposed a-IGZO APS x-ray imager with a pixel pitch <75 µm is capable to achieve a high spatial frequency (>6.67 lp/mm) and a low dose (<0.4 mGy) in next generation DBT systems [ABSTRACT FROM AUTHOR]

In this letter, the electrical properties of bottom-gate and dual gate (DG) amorphous In-Ga-Zn-O (a-IGZO) metal–semiconductor field-effect transistors (MESFETs) are studied by a 2-D numerical simulation. A subgap density of state model is proposed and used in the simulation. The bottom gate MESFET shows field-effect mobility (\mu\rm{FE}) of 9 cm^2/Vs, threshold voltage (V\rm{th}) of -6.3~V, and subthreshold swing of 0.12 V/decade. The DG a-IGZO MESFET structure is suggested to effectively increase the device operational current (I\rm{on}). [ABSTRACT FROM AUTHOR]