Circular Field Of View Research Articles

Command filtered integrated estimation guidance and control for strapdown missiles with circular field of view

In this paper, an integrated estimation guidance and control (IEGC) system is designed based on the command filtered backstepping approach for circular field-of-view (FOV) strapdown missiles. The three-dimensional integrated estimation guidance and control nonlinear model with limited actuator deflection angle is established considering the seeker's FOV constraint. The boundary time-varying integral barrier Lyapunov function (IBLF) is employed in backstepping design to constrain the body line-of-sight (BLOS) in IEGC system to fit a circular FOV. Then, the nonlinear adaptive controller is designed to estimate the changing aerodynamic parameters. The generalized extended state observer (GESO) is designed to estimate the acceleration of the maneuvering targets and the unmatched time-varying disturbances for improving tracking accuracy. Furthermore, the command filters are used to solve the "differential expansion" problem during the backstepping design. The Lyapunov theory is used to prove the stability of the overall closed-loop IEGC system. Finally, the simulation results validate the integrated system's effectiveness, achieving high accuracy strikes against maneuvering targets.

Speculum-free portable preterm imaging system.

Preterm birth is defined as a birth before 37 weeks of gestation and is one of the leading contributors to infant mortality rates globally. Premature birth can lead to life-long developmental impairment for the child. Unfortunately, there is a significant lack of tools to diagnose preterm birth risk, which limits patient care and the development of new therapies. To develop a speculum-free, portable preterm imaging system (PPRIM) for cervical imaging; testing of the PPRIM system to resolve polarization properties of birefringent samples; and testing of the PPRIM under an IRB on healthy, non-pregnant volunteers for visualization and polarization analysis of cervical images. The PPRIM can perform Mueller-matrix imaging to characterize the remodeling of the uterine cervix during pregnancy. The PPRIM is built with a polarized imaging probe and a flexible insertable sheath made with a compatible flexible rubber-like material to maximize comfort and ease of use. The PPRIM device is developed to meet specific design specifications as a speculum-free, portable, and comfortable imaging system with polarized imaging capabilities. This system comprises a main imaging component and a flexible silicone inserter. The inserter is designed to maximize comfort and usability for the patient. The PPRIM shows high-resolution imaging capabilities at the 20mm working distance and 25mm circular field of view. The PPRIM demonstrates the ability to resolve birefringent sample orientation and full field capture of a healthy, non-pregnant cervix. The development of the PPRIM aims to improve access to the standard of care for women's reproductive health using polarized Mueller-matrix imaging of the cervix and reduce infant and maternal mortality rates and better quality of life.

Polar coordinate Fourier single-pixel imaging.

Traditional single-pixel imaging uses Fourier patterns to modulate objects in the Cartesian coordinate system. The Cartesian Fourier pattern of single-pixel imaging is inappropriate to display in a circular field of view. However, a circular field of view is a widespread form of display in computed optical imaging. Here, circular patterns are adopted to adapt to the circular visual area. The circular patterns are displayed in polar coordinates and derived from two-dimensional Fourier transform in polar coordinates. The proposed circular patterns have improved imaging efficiency significantly from 63.66% to 100%. The proposed polar coordinate Fourier single-pixel imaging is expected to be applied in circular field-of-view imaging and foveated imaging.

Metis: the Solar Orbiter visible light and ultraviolet coronal imager

Aims. Metis is the first solar coronagraph designed for a space mission and is capable of performing simultaneous imaging of the off-limb solar corona in both visible and UV light. The observations obtained with Metis aboard the Solar Orbiter ESA-NASA observatory will enable us to diagnose, with unprecedented temporal coverage and spatial resolution, the structures and dynamics of the full corona in a square field of view (FoV) of ±2.9° in width, with an inner circular FoV at 1.6°, thus spanning the solar atmosphere from 1.7R⊙to about 9R⊙, owing to the eccentricity of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter mission profile, Metis will be able to observe the solar corona from a close (0.28 AU, at the closest perihelion) vantage point, achieving increasing out-of-ecliptic views with the increase of the orbit inclination over time. Moreover, observations near perihelion, during the phase of lower rotational velocity of the solar surface relative to the spacecraft, allow longer-term studies of the off-limb coronal features, thus finally disentangling their intrinsic evolution from effects due to solar rotation.Methods. Thanks to a novel occultation design and a combination of a UV interference coating of the mirrors and a spectral bandpass filter, Metis images the solar corona simultaneously in the visible light band, between 580 and 640 nm, and in the UV H ILyman-αline at 121.6 nm. The visible light channel also includes a broadband polarimeter able to observe the linearly polarised component of the K corona. The coronal images in both the UV H ILyman-αand polarised visible light are obtained at high spatial resolution with a spatial scale down to about 2000 km and 15 000 km at perihelion, in the cases of the visible and UV light, respectively. A temporal resolution down to 1 s can be achieved when observing coronal fluctuations in visible light.Results. The Metis measurements, obtained from different latitudes, will allow for complete characterisation of the main physical parameters and dynamics of the electron and neutral hydrogen/proton plasma components of the corona in the region where the solar wind undergoes the acceleration process and where the onset and initial propagation of coronal mass ejections (CMEs) take place. The near-Sun multi-wavelength coronal imaging performed with Metis, combined with the unique opportunities offered by the Solar Orbiter mission, can effectively address crucial issues of solar physics such as: the origin and heating/acceleration of the fast and slow solar wind streams; the origin, acceleration, and transport of the solar energetic particles; and the transient ejection of coronal mass and its evolution in the inner heliosphere, thus significantly improving our understanding of the region connecting the Sun to the heliosphere and of the processes generating and driving the solar wind and coronal mass ejections.Conclusions. This paper presents the scientific objectives and requirements, the overall optical design of the Metis instrument, the thermo-mechanical design, and the processing and power unit; reports on the results of the campaigns dedicated to integration, alignment, and tests, and to the characterisation of the instrument performance; describes the operation concept, data handling, and software tools; and, finally, the diagnostic techniques to be applied to the data, as well as a brief description of the expected scientific products. The performance of the instrument measured during calibrations ensures that the scientific objectives of Metis can be pursued with success.

Compact, unit magnification, reflective imaging relay using freeform surfaces

We present a design for a unit magnification imaging relay that is compact. The design uses two mirrors, and one is used by light twice for a three-reflection system. The mirrors are specified with freeform surfaces. There are several tradeoffs of performance depending on field of view, F / #, and wavelength range. One example provides a 30-mm circular field of view at F / 2.8, and another example provides a circular field of view of 40 mm in diameter at F / 4 for a length of ∼400 mm. Adding a third nearly flat mirror allows a system to provide a 50-mm field of view at F / 4 for a length of 420 mm. A last example includes a beam splitter cube to allow accessing the full field of view. These systems are diffraction limited at 550 nm.

Comments on the 2013 ICNIRP Laser Guidelines.

Comments on the 2013 ICNIRP Laser Guidelines.

Analytic Determination of Rectangular-Pinhole Sensitivity With Penetration.

Modern small-animal SPECT systems use multiple pinhole collimators per detector to increase sensitivity while still maintaining high resolution. This resolution is a combination of aperture resolution combined with detector resolution, which is mitigated by magnification. Higher magnification results in better resolution, but fewer apertures per detector. When multiple pinhole collimators project onto the same detector, those with a rectangular field of view (FOV) can be packed more tightly than those with a circular FOV. In addition, a rectangular aperture can be used to obtain different resolution-sensitivity tradeoffs in the two orthogonal directions. Thus, these rectangular-pinhole collimators can have independent FOVs and independent resolution values in the two directions of the rectangular aperture. Previous work has determined the amount of penetration for circular pinholes (i.e., circular apertures with circular FOVs), where the pinhole walls were modeled as cones. In this work, a formula for the penetrative sensitivity for rectangular apertures with a rectangular FOV is determined. The formula was validated using numerical calculations for various combinations of acceptance angles, aperture sizes, linear attenuation coefficients, and incidence angles.

Spatial properties of soil analyses and airborne measurements for reconnaissance of soil contamination by 137Cs after Fukushima nuclear accident in 2011

Following Fukushima nuclear disaster, several data gathering campaigns surveyed the radionuclide propagation in the environment. However, the acquired datasets do not have the same sampling dimension. For example, the airborne measurements are some sort of averaging over a circular field of view, beneath the sensor; while the soil analyses are much more punctual. The objective of this work is to compare the soil samples and an airborne survey to investigate whether these two datasets reflect the same spatial patterns or not. This is prerequisite for combining the multiresolution data to create and update the contamination map in a post-accidental situation.The analyses were performed on square tiles of 20 km side to study large- and small-dimension variations in 137Cs deposition. The former was modelled by fitting a plane (called trend) to the georeferenced data points; and the latter was modelled by computing the difference (called residual) between the trend and the initial data. Dip direction and dip angle of trends as well as minimum spatial correlation distance and anisotropy of residuals were computed for both the soil and airborne datasets and compared. Dip directions are compatible in 73% of the tiles and dip angles are generally close. Anisotropy directions are compatible in 49% of the tiles and minimum spatial correlation distances are significantly more marked for the airborne dataset.The soil samples and airborne measurements are therefore more in agreement in large-dimension (trend) rather than in small-dimension (residual) variations. More generally, both the datasets allow highlighting the main contamination plumes distinguishable because of high concentration values. The airborne dataset yet appears to be more powerful to quantify spatial correlations, which could be linked to the contamination mechanisms.

Trajectory analysis for field free line magnetic particle imaging.

Magnetic particle imaging (MPI) is a relatively new method to image the spatial distribution of magnetic nanoparticle (MNP) tracers administered to the body with high spatial and temporal resolution using an inhomogeneous magnetic field. The spatial information of the MNP's is encoded using a field free point (FFP), or a field free line (FFL), in which the magnetic field vanishes at a point, or on a line, respectively. FFL scanning has the advantage of improved sensitivity compared to FFP scanning as a result of higher signal-to-noise ratio. The trajectory traversed by the FFL or FFP is an important parameter of the MPI system and should be selected to achieve the best imaging quality in minimum scan time, while considering hardware constraints and patient safety. In this study, we analyzed the image quality of different FFL trajectories for a large field of view (FOV) using simulations, to provide a baseline information for FFL scanning MPI system design. We simulated a human-sized FFL scanning MPI configuration to image a circular FOV with 160mm diameter, and compared Radial, Spiral, Uniform Spiral, Flower, and Lissajous trajectories with different trajectory densities scanned by the FFL for constant scan time. We analyzed the system matrices of the trajectories in terms of mutual coherence and homogeneity of the spatial sensitivity. We calculated the maximum electric fields induced on a homogeneous conductive body by the selection field (SF) and the focus field (FF) to compare the trajectories based on the nerve stimulation threshold. The images were obtained using the system matrix reconstruction approach with two different image reconstruction methods. In the first one, we used the conventional image reconstruction method, algebraic reconstruction technique (ART), which gives a regularized least-squares solution. In the second one, we used the state-of-the-art alternating direction method of multipliers (ADMM), which minimizes a weighted sum of the l1 -norm and the total variation (TV) of the images. The Radial and Spiral trajectories resulted in a poor imaging performance at low trajectory densities due to relatively high coherency and poor sensitivity of the measurements, respectively. For ART reconstruction, the highest image quality with the lowest trajectory density was achieved with the Uniform Spiral trajectory. Uniform Spiral, Flower, and Lissajous trajectories yielded comparable performance with ADMM reconstruction. The rotating SF induced higher electric field amplitude compared to the FF. Consequently, maximum allowable gradient at the same trajectory density was greater for the Radial trajectory compared to the other trajectories. For a large FOV coverage, the Uniform Spiral trajectory offers a good compromise between image quality and imaging time, taking safety and hardware limitations into account. The Radial trajectory, especially using l1 -norm and TV priors in the reconstruction, may be favorable in case the SF induced electric field is higher than that of the FF at the same frequency (e.g., relatively small FOV coverage). In general, ADMM reconstruction resulted in higher contrast and resolution compared to ART, leading to lighter requirements on the density of the trajectory.

Anisotropic field-of-view support for golden angle radial imaging.

To provide anisotropic field-of-view (FOV) support for golden angle radial imaging. In radial imaging, uniform spoke density leads to a circular FOV, which is excessive for objects with anisotropic dimensions. Larson et al previously showed that the angular k-space spoke density can be determined by the desired anisotropic FOV. We show that conventional golden angle sampling can be deployed in an angle-normalized space and transformed back to k-space such that the desired nonuniform spoke density is preserved for arbitrary temporal window length. Elliptical FOVs were used to illustrate this generalized mapping approach. Point-spread-function and spoke density analysis was performed. Phantom and in vivo cardiac images were acquired. Simulations, phantom, and in vivo experiments confirmed that the proposed method is able to achieve anisotropic FOV while still maintaining the benefits of golden angle sampling. This approach requires 50% less spokes for elliptical FOV with major-to-minor-axis ratio of 1:0.3, when compared with isotropic FOV with the same undersampling factor. We demonstrate a simple method for applying golden angle view ordering to anisotropic FOV radial imaging. This can reduce imaging time for objects with anisotropic dimensions while still allowing arbitrary temporal window selection. Magn Reson Med 76:229-236, 2016. © 2015 Wiley Periodicals, Inc.

Dynamic detector offsets for field of view extension in C-arm computed tomography with application to weight-bearing imaging.

In C-arm computed tomography (CT), the field of view (FOV) is often not sufficient to acquire certain anatomical structures, e.g., a full hip or thorax. Proposed methods to extend the FOV use a fixed detector displacement and a 360° scan range to double the radius of the FOV. These trajectories are designed for circular FOVs. However, there are cases in which the required FOV is not circular but rather an ellipsoid. In this work, the authors show that in fan-beam CT, the use of a dynamically adjusting detector offset can reduce the required scan range when using a noncircular FOV. Furthermore, the authors present an analytic solution to determine the minimal required scan ranges for elliptic FOVs given a certain detector size and an algorithmic approach for arbitrary FOVs. The authors show that the proposed method can result in a substantial reduction of the required scan range. Initial reconstructions of data sets acquired with our new minimal trajectory yielded image quality comparable to reconstructions of data acquired using a fixed detector offset and a full 360° rotation. Our results show a promising reduction of the necessary scan range especially for ellipsoidal objects that extend the FOV. In noncircular FOVs, there exists a set of solutions that allow a trade-off between detector size and scan range.

SU‐E‐I‐50: Ultrahigh Resolution Reduced Field‐Of‐View Diffusion Tensor Imaging in the Spinal Cord

Purpose:Diffusion Tensor Imaging (DTI) is a well‐established MRI imaging modality for applications in the brain. The typically attainable imaging resolution for clinical DTI sequences is insufficient to image small lesions and assess injury with microstructural changes in the spinal cord (SC). Attempts to reduce the field‐of‐view (FOV) for increasing the imaging resolution have been made using rectangular FOV geometries that work well to efficiently image the sagittal plane. The highest structural details in the SC are however in the axial plane, most efficiently covered by a circular FOV. The aim of this study was to increase the axial DTI resolution in the SC to distinguish the dorsal spinal white‐matter bundles within clinically acceptable acquisition times.Methods:A multishot reduced FOV DTI technique named eZOOM that utilizes spatially selective radio‐frequency (RF) pulses and spiral readout has recently been developed by the author (Gaggl, MRM 2014) for application in the brain. In this study the method was adapted to the unique geometry of multichannel spinal RF coil arrays, with improved correction of blurring and misregistration and including peripheral gating to minimize cerebrospinal fluid flow‐artifacts. Several diffusion metrics including the novel normalized axial diffusivity DAn=λ1/∑λ (Gaggl, ASFNR 2013) were calculated and compared to current methods.Results:Sub‐millimeter square‐voxel imaging resolutions with image voxel volumes of approximately 1mm3 for a circular axial 8‐cm FOV and 15 diffusion weighting gradient directions were achieved in human for multislice image stacks in the SC with total imaging times of less than 30 minutes at 3T, enabling the separation of important spinal fiber tracts.Conclusion:The presented technique improves imaging resolution for DTI in the spinal cord compared to current clinical sequences while allowing to prescribe imaging geometries that excite only a small axial circular FOV in and around the spinal cord and reducing blurring and artifacts.

Star Covering Region Evaluation with Application to Star Tracker Design

The performance of a star tracker is closely linked to the characteristics of the guide star catalog. It is an essential part of design to estimate the number of guide stars observed by the star tracker in any given boresight direction. This paper reports on the star covering region evaluation method, which is used to find ranges of orientation where the star tracker can observe a star. With this method, a conservative number of guide stars observed by the star tracker in any given boresight direction can be quantitatively evaluated and credible ranges of orientation can be found, where the star tracker can observe enough guide stars to perform autonomous star identification; thus, verifying the design of the star tracker. The celestial sphere is divided into 131,072 approximately congruent spherical triangles, such that the star’s covering region can be approximately depicted by triangles in which the circumcenters are close enough to the star. Then, the stars observed by the tracker, in which the boresight is located anywhere inside the circumcircle of the triangle, can be found by identifying where the triangle is located in a given star’s covering region. A guide star catalog containing 2,873 stars was generated and the star covering region evaluation was performed. It was found that the star tracker with a circular field of view (FOV) radius of 4° could measure at least three guide stars when its boresight direction was located in 63,554 spherical triangles. The evaluation results for 10,000 random orientations were used to compare the counting numbers of practically observed stars. The mean error is 0.6415 and the maximum error is 5, which results from the stars not considered because they are on the edge of the FOV. The results of a simulation have validated the method.

Optical design of a full-pupil field, non-contact and high resolution corneal curved objective lens

It has been a challenge to overcome the corneal curvature radius to design a full-pupil field, non-contact and high resolution corneal curved objective lens, which covers the cornea full-pupil field and has the ability to resolve corneal cells. In this paper, we report an optical design of a full-pupil field, non-contact corneal curved objective lens for high resolution cornea imaging. The advantages of this lens are that it has a wide field of view (FOV) with the corneal curved image surface, maintains the beam normal incidence, as well as non-contact lens imaging, and offers a cell-level lateral resolution of cornea structure. The analysis of optimization shows that the system achieves diffraction limit in a circular FOV of 4mm diameter covering the full-pupil zone. The theoretical lateral resolution is about 2.5μm with an image space NA of 0.16, which is sufficient to resolve corneal cells of 7μm diameter, and the working distance is larger than 15mm which is enough for a non-contact objective lens. So the optical design is effectively and efficiently meeting the demand of specifications.

Image domain propeller fast spin echo

A new pulse sequence for high-resolution T2-weighted (T2-w) imaging is proposed — image domain propeller fast spin echo (iProp-FSE). Similar to the T2-w PROPELLER sequence, iProp-FSE acquires data in a segmented fashion, as blades that are acquired in multiple TRs. However, the iProp-FSE blades are formed in the image domain instead of in the k-space domain. Each iProp-FSE blade resembles a single-shot fast spin echo (SSFSE) sequence with a very narrow phase-encoding field of view (FOV), after which N rotated blade replicas yield the final full circular FOV. Our method of combining the image domain blade data to a full FOV image is detailed, and optimal choices of phase-encoding FOVs and receiver bandwidths were evaluated on phantom and volunteers. The results suggest that a phase FOV of 15–20%, a receiver bandwidth of ±32–63 kHz and a subsequent readout time of about 300 ms provide a good tradeoff between signal-to-noise ratio (SNR) efficiency and T2 blurring. Comparisons between iProp-FSE, Cartesian FSE and PROPELLER were made on single-slice axial brain data, showing similar T2-w tissue contrast and SNR with great anatomical conspicuity at similar scan times — without colored noise or streaks from motion. A new slice interleaving order is also proposed to improve the multislice capabilities of iProp-FSE.

The Hα observations of the California Nebula (NGC 1499) with DEFPOS

AbstractA dual étalon Fabry‐Pérot spectrometer called DEFPOS has been used for observing physical properties of HII regions and planetary nebulae since May 2007 (Aksaker et al. 2009, 2011; Şahan et al. 2009; Şahan 2011). In this study, the Hα measurements of the HII region NGC 1499 (California Nebula) have been investigated with a 4′ circular field of view over a 200 km s–1 (4.4 Å) spectral window. These measurements provide information about the densities, line widths, and radial velocities of the surrounding NGC 1499 nebula. The intensities, the radial velocities and the line widths of the Hα emission line vary from 397.75 R to 1044.14 R, –4.88 km s–1 to –1.02 km s–1, and 36.72 km s–1 to 42.81 km s–1, respectively (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Toward high-sensitivity and high-resolution submillimeter-wave video imaging

Against a background of newly emerged security threats, the well-established idea of utilizing submillimeter-wave radiation for personal security screening applications has recently evolved into a promising technology. Possible application scenarios demand sensitive, fast, flexible and high-quality imaging techniques. At present, best results are obtained by passive imaging using cryogenic microbolometers as radiation detectors. Building upon the concept of a passive submillimeter-wave stand-off video camera introduced previously, we present the evolution of this concept into a practical application-ready imaging device. This has been achieved using a variety of measures such as optimizing the detector parameters, improving the scanning mechanism, increasing the sampling speed, and enhancing the image generation software. The camera concept is based on a Cassegrain-type mirror optics, an optomechanical scanner, an array of 20 superconducting transition-edge sensors operated at a temperature of 450 to 650 mK, and a closed-cycle cryogen-free cooling system. The main figures of the system include: a frequency band of 350±40 GHz, an object distance of 7 to 10 m, a circular field of view of 1.05 m diameter, and a spatial resolution in the image center of 2 cm at 8.5 m distance, a noise equivalent temperature difference of 0.1 to 0.4 K, and a maximum frame rate of 10 Hz.

High-resolution resonant and nonresonant fiber-scanning confocal microscope

We present a novel, hand-held microscope probe for acquiring confocal images of biological tissue. This probe generates images by scanning a fiber-lens combination with a miniature electromagnetic actuator, which allows it to be operated in resonant and nonresonant scanning modes. In the resonant scanning mode, a circular field of view with a diameter of 190 μm and an angular frequency of 127 Hz can be achieved. In the nonresonant scanning mode, a maximum field of view with a width of 69 μm can be achieved. The measured transverse and axial resolutions are 0.60 and 7.4 μm, respectively. Images of biological tissue acquired in the resonant mode are presented, which demonstrate its potential for real-time tissue differentiation. With an outer diameter of 3 mm, the microscope probe could be utilized to visualize cellular microstructures in vivo across a broad range of minimally-invasive procedures.

Laser-scanning optical-resolution photoacoustic microscopy

We have developed a laser-scanning optical-resolution photoacoustic microscopy method that can potentially fuse with existing optical microscopic imaging modalities. To acquire an image, the ultrasonic transducer is kept stationary during data acquisition, and only the laser light is raster scanned by an x-y galvanometer scanner. A lateral resolution of 7.8 microm and a circular field of view with a diameter of 6 mm were achieved in an optically clear medium. Using a laser system working at a pulse repetition rate of 1,024 Hz, the data acquisition time for an image consisting of 256 x 256 pixels was less than 2 min.

Hα measurements using DEFPOS/RTT150 Telescope: Instrumentation and observations

To investigate the physical properties of HII regions and some PNe about 4′ in size, a DEFPOS Fabry–Perot spectrometer has been redesigned and set up at the coudé exit of the 150 cm RTT150 telescope (f/48) at TUBITAK National Observatory (Antalya/Bak\U0001d6a4rl\U0001d6a4tepe, Turkey). The spectrometer has a 4′ circular field of view and a velocity resolution of 27.27 km s−1 (a spectral resolving power of 11000) over a 200 km s−1 spectral window near Hα. This work presents the details of the newly redesigned instrument for coudé observations, the data reduction techniques and finally presents some physical results of our new Hα observations selected from the Reynolds et al. (2005) and Fich et al. (1990) papers. The DEFPOS system has been fully tested and the first observations of HII regions and PNe in the Galaxy are used to illustrate the power of the instrument. We feel that our first Fabry–Perot observations can provide a powerful tool for the study of objects with small angular size. In the future, we are planning to prepare a catalog including some physical properties such as radial velocity, line width, and intensity of some PNe and HII regions close to the 4′ field of view.