Image MTF Research Articles

Super-agile satellites imaging mission planning method considering degradation of image MTF in dynamic imaging

Super-agile satellites with dynamic imaging capabilities can significantly improve the imaging efficiency of space-borne Earth observation. However, the image modulation transfer function (image MTF) of dynamic imaging varies dramatically with changes in the attitude maneuver status while improving observation efficiency. Therefore, both the observation efficiency and image MTF should be considered in the imaging mission planning of super-agile satellites. Existing imaging mission planning methods are mainly aimed at traditional agile satellites that are not capable of dynamic imaging, and the mainly optimization objectives are coverage revenue, spatial resolution, and task performance time, without considering the observation efficiency and image MTF as the optimization objectives. To overcome the problem of image MTF degradation caused by dynamic imaging, a mission planning method which considers the degradation of the image MTF and observation efficiency was proposed. Firstly, a mapping relationship between the angular velocity of the attitude maneuvering and the image MTF was constructed. On this basis, a Pareto multi-objective imaging mission planning model of partial order based was established. Considering the particularity of the model, the non-dominated sorting strategy of the NSGA-II algorithm was redesigned when solving the model using NSGA-II algorithm. Finally, the imaging tasks of different scales in single satellite and multi-satellite simulation scenes were set, and the proposed imaging mission planning method was verified. The planning results showed that the proposed method can achieve a balanced optimization of the image MTF and task efficiency under the premise of ensuing maximum observation coverage revenue.

50.5: Pupil Swim Measurement and Analysis of Near‐eye displays

Pupil swim is defined as the perceived change of image quality as the eye moves or rotates within the system pupil or eyebox. This will lead to the change of image distortion, lateral chromatic aberration, and MTF. Pupil swim will make people uncomfortable as the eye rotates off the center axis and across the lens. Even with perfect distortion correction at the center viewing position the user will still experience some distortion when moving the eye around because the distortion field at the edge is different than the field in the center. In this paper, pupil swim is measured using near-eyedisplay measurement system and the change of image displacement and distortion are calculated. The simulation and measurement results show the virtual image under different pupil position has shifted and the distortion at different pupil position is different.

Optical satellite image MTF compensation for remote-sensing data production

Optical satellite image MTF compensation for remote-sensing data production

Integrated 3D display and imaging using dual purpose passive screen and head-mounted projectors and camera.

We propose an integrated 3D display and imaging system using a head-mounted device and a special dual-purpose passive screen that can simultaneously facilitate 3D display and imaging. The screen is mainly composed of two optical layers, the first layer is a projection surface, which are the finely patterned retro-reflective microspheres that provide high optical gain when illuminated with head-mounted projectors. The second layer is an imaging surface made up of an array of curved mirrors, which form the perspective views of the scene captured by a head-mounted camera. The display and imaging operation are separated by performing polarization multiplexing. The demonstrated prototype system consists of a head-worn unit having a pair of 15 lumen pico-projectors and a 24MP camera, and an in-house designed and fabricated 30cm × 24cm screen. The screen provides bright display using 25% filled retro-reflective microspheres and 20 different perspective views of the user/scene using 5 × 4 array of convex mirrors. The real-time implementation is demonstrated by displaying stereo-3D content providing high brightness (up to 240 cd/m2) and low crosstalk (<4%), while 3D image capture is demonstrated by performing the computational reconstruction of the discrete free-viewpoint stereo pair displayed on a desktop or virtual reality display. Furthermore, the capture quality is determined by measuring the imaging MTF of the captured views and the capture light efficiency is calculated by considering the loss in transmitted light at each interface. Further developments in microfabrication and computational optics can present the proposed system as a unique mobile platform for immersive human-computer interaction of the future.

SU-F-207-12: Optimal CT Scan Mode and Reconstruction Kernel Selection for Bone Fracture Detection Task Under Both Centered and Off-Centered Conditions

Purpose: Hi-Res(olution) mode was introduced in some state-of-the-art CT systems to reduce aliasing and improve spatial resolution. The Hi-Res data can be reconstructed using either the conventional kernels or HD kernels. Since high spatial resolution is often associated with a tremendous increase in image noise, the introduction of Hi-Res has confounded the scan protocol optimization. This work investigated how to use the task-driven optimization framework to optimize the selection of Hi-Res mode and reconstruction kernel for bone fracture detection tasks. Methods: The dependence of spatial resolution on scan mode, reconstruction kernel and off-center position was quantified via MTF measurements. For certain edge enhancing Hi-Res kernels, accuracy of the measurements was confounded by both high image noise and potential CT number saturations. These challenges were addressed by a combined use of repeated scanning and thick-slice reconstructions. Similarly, the NPS was measured under different conditions from repeated scans. The frequency-dependent detectability analysis was used to combine imaging task, MTF, and NPS to quantify the dependence of the overall imaging performance and optimize scan mode and reconstruction kernel selection. Results: (1) For a conventional kernel, the use of Hi-Res significantly improved the MTF at off-centered position. (2) The combined use of Hi-Res mode and HD kernel improved MTF at both the centered and off-centered positions. (3) The use of HD kernels increased noise magnitude and pushed the NPS to higher frequencies, and a model-observer analysis demonstrated that the optimal kernel and scan mode strongly depends on patient position and the nature of the task. This was confirmed by ex vivo animal (bovine bone) experiment. Conclusion: Optimal use of the Hi-Res mode and its associated HD kernels depends on patient positioning and the imaging task. Optimal decision making for its use can be achieved based on the framework developed in this work. J. P. Cruz Bastida, D. Gomez-Cardona, K. Li: Nothing to disclose. T. P. Szczykutowicz: Equipment support, General Electric Company Research Grant, Siemens AG. G.-H. Chen: Research funded, GE Healthcare; Research funded, Siemens AX.

基于MTF辅助正焦判断的自动调焦搜索算法

Traditional climbing search algorithm cannot usually focusing accurately due to the interference of evaluation function local extremum effected by measure environment.A searching algorithm of autofocusing based on MTF auxiliary focal judgment was introduced to improve the climbing method. Definition evaluation function and MTF values of images were considered at the same time.And based on those results,search direction was judged.Slanted-edge method was improved to calculate the image MTF values accurately based on the auto-selection of slanted-edge area.At last,the principle and implementation of the improved algorithm was given.In the theodolite auto-fousing system,the system imaging effect was validated,and different initial position and circumstance were considered using the proposed searching algorithm.The experiment results of theodolite auto-focus system show that the improved climbing search algorithm can effectively eliminate the local extremum disturbance,and make the system searching focusing accurately and reliably.

Imaging performance with turret aero-optical wavefront disturbances

We modeled the imaging performance of an acquisition, tracking, and pointing sensor when operating on a high-speed aircraft platform through a turreted laser beam director/telescope. We applied standard scaling relations to wavefront sensor (WFS) data collected from the Airborne Aero-Optics Laboratory test platform operating at Mach 0.5 to model aero-optical aberrations for a λ=1 μm wavelength laser system with a D ap =30 cm aperture diameter and a 90-cm turret diameter on a platform operating at 30 kft and for speeds of Mach 0.4 to 0.8. Using these data, we quantified the imaging point spread function for each aircraft speed. Our simulation results show Strehl ratios from 0.1 to 0.8 with substantial scattering of energy out to 7.5× the diffraction-limited core. Analysis of the imaging MTF shows a rapid reduction of contrast for low-to-mid range spatial frequencies with an increasing Mach number. Low modulation contrast at higher spatial frequencies limits imaging resolution to >2× diffraction-limit at Mach 0.5 and 5× diffraction-limit at Mach 0.8. Practical limits to usable spatial frequencies require higher image signal to noise ratio in the presence of aero-optical disturbances at a high Mach number. Illuminator laser propagation through aero-optical aberrations produces target illumination modulation at scale sizes near the diffraction-limit of the transmitting laser aperture, thereby producing illumination artifacts that can degrade image-contrast-based tracking algorithms.

디지털 방사선시스템에서 영상증강 파라미터의 영상특성 평가

Digital imaging detectors can use a variety of detection materials to convert X-ray radiation either to light or directly to electron charge. Many detectors such as amorphous silicon flat panels, CCDs, and CMOS photodiode arrays incorporate a scintillator screen to convert x-ray to light. The digital radiography systems based on semiconductor detectors, commonly referred to as flat panel detectors, are gaining popularity in the clinical & hospital. The X-ray detectors are described between a-Silicon based indirect type and a-Selenium based direct type. The DRS of detectors is used to convert the x-ray to electron hole pairs. Image processing is described by specific image features: Latitude compression, Contrast enhancement, Edge enhancement, Look up table, Noise suppression. The image features are tuned independently. The final enhancement result is a combination of all image features. The parameters are altered by using specific image features in the different several hospitals. The image in a radiological report consists of two image evaluation processes: Clinical image parameters and MTF is a descriptor of the spatial resolution of a digital imaging system. We used the edge test phantom and exposure procedure described in the IEC 61267 to obtain an edge spread function from which the MTF is calculated. We can compare image in the processing parameters to change between original and processed image data. The angle of the edge with respect to the axes of detector was varied in order to determine the MTF as a function of direction. Each MTF is integrated within the spatial resolution interval of 1.35-11.70 cycles/mm at the 50% MTF point. Each image enhancement parameters consists of edge, frequency, contrast, LUT, noise, sensitometry curve, threshold level, windows. The digital device is also shown to have good uniformity of MTF and image parameters across its modality. The measurements reported here represent a comprehensive evaluation of digital radiography system designed for use in the DRS. The results indicate that the parameter enables very good image quality in the digital radiography. Of course, the quality of image from a parameter is determined by other digital devices in addition to the proper clinical image.

SU-FF-I-18: Optimization of FDK Reconstruction Parameters to Minimize Aliasing and Reduce Metal Artifacts

Purpose: To maximize SNR, suppress metal artifacts and minimize backprojection times for FDK-based cone-beam CT (CBCT) reconstructions by optimizing binning, filtering and backprojection parameters, and to investigate the performance of new multi-core CPU's. Methods and Materials: CBCT reconstruction times can be reduced by filtering and downsampling high resolution flat panel projection data to match the reconstruction matrix pitch, and by using nearest neighbor interpolation (NN) for backprojection. However, metal artifacts and noise aliasing may result. To investigate the tradeoffs involved, a frequency-domain noise power spectrum (NPS) model was developed. Phantom and clinical CBCT data were acquired using the On-Board Imager and reconstructed with a range of pre-processing and backprojection parameters while keeping image MTF constant. Image noise, including the amount of noise aliasing, and metal artifacts were evaluated. Reconstruction times were measured on Xeon workstations comprising either two single-core, dual-core, or quad-core CPU's. Results: Two types of metal artifacts emerged. A moiré pattern is produced if insufficient projection data densities in the transaxial direction are maintained, while radial streaks are produced by insufficiently dense axial data. For best image quality aliased noise should be less than 5% of the total image noise, and projection data should be 1.5–2.0× denser than the reconstructed image matrix pitch for backprojection with bilinear interpolation. NN interpolation is not preferred. Although backprojection times increased by ∼50% with these higher projection data densities, overall reconstruction times for relatively large image matrices (512×512×188, 675 projections), were <50 seconds using the quad-core workstation which is sufficiently fast for IGRT applications. Conclusions: Optimal use of high data densities coupled with bilinear interpolation for backprojection can suppress some metal artifacts and minimize noise aliasing. New multi-core CPU architectures provide sufficient speed to make such reconstructions clinically practical. Conflict of Interest: Employees of Varian Medical Systems.

An evaluation of the Y2O3:Eu3+ scintillator for application in medical x-ray detectors and image receptors.

The suitability off a Y2O3:Eu3+ scintillator for use in radiation detectors and medical image receptors was studied. Y2O3:Eu3+ was used in the form of laboratory prepared screens of different coating thicknesses. The x-ray luminescence efficiency of the screens was measured for tube voltages between 50-200 kVp and in both transmission and reflection modes of observation. The intrinsic x ray to light conversation efficiency (nc) and other parameters of the Y2O3:Eu3+ phosphor material related to optical scattering, absorption, and reflection were determined. These were used in the calculation of the image transfer characteristics, MTF and zero frequency DQE, for various screen coating thicknesses and x-ray tube voltages. The light emission spectrum of Y2O3:Eu3+ was measured (narrow band peak at 613 nm) and its spectral compatibility to the spectral sensitivity of several commonly employed optical photon detectors was determined. The x-ray luminescence efficiency varied with x-ray tube voltage, attaining maximum value at about 80 kVp for all screen thicknesses. It also varied with coating thickness reaching 25 microW m(-2)/mR s(-1) and 18 microW m(-2)/mR s(-1) at 175 mg/cm2 for reflection and transmission modes, respectively. The intrinsic x ray to light conversion efficiency and the image transfer characteristics were found to be comparable to several commercially used phosphors: nc = 0.095, MTF0.05 ranged between 10 and 25 line pairs per mm and peal values of DQE(0) varied between 0.33 and 0.14 in the coating thickness and kVp ranges useful for x-ray imaging. Spectral compatibility to some red sensitive optical photon detectors was excellent (0.9 or better). Results indicated that Y2O3:Eu3+ is a medium to high overall performance material that could be used in medical x-ray detectors and image receptors.

The Calculation of Dye Cloud MTF and Point Spread Function in Colour Negative Photographic Materials

AbstractIt is shown that the MTF associated with the dye cloud structure in colour negative photographic materials can be calculated from measurements made of the colour image MTF and the developed silver image MTF. Determinations of dye cloud MTF were made for a series of experimental single emulsion layer colour negative materials in which the dye cloud projective area was systematically varied. This was achieved by a variation in image coupler coating weight. The blanket transform of the dye cloud MTF yields a point spread function, and a correlation was found between this function and the actual dye cloud area as determined photomicrograpliically. For all dye cloud sizes, it was found that MTF degradation due to the silver to dye transformation process is confined to spatial frequencies above 20c/mm. Differences in dye cloud MTF due to dye cloud size variation occurred at spatial frequencies above 50 c/mm. For the photographic materials examined, the degradation in colour image MTF incurred through Ih...