Effective Imaging Area Research Articles

Numerical design of transverse gradient coil with transformed magnetic gradient field over an effective imaging area

Numerical design of transverse gradient coil with transformed magnetic gradient field over an effective imaging area

Modeling of Rapid Pam Systems Based on Electrothermal Micromirror for High-Resolution Facial Angiography.

In this paper, a portable photoacoustic microscopy (PAM) system is proposed based on a large stroke electrothermal micromirror to achieve high resolution and fast imaging. The crucial micromirror in the system realizes a precise and efficient 2-axis control. Two different designs of electrothermal actuators with "O" and "Z" shape are evenly located around the four directions of mirror plate. With a symmetrical structure, the actuator realized single direction drive only. The finite element modelling of both two proposed micromirror has realized a large displacement over 550 μm and the scan angle over ±30.43° at 0-10 V DC excitation. In addition, the steady-state and transient-state response show a high linearity and quick response respectively, which can contribute to a fast and stable imaging. Using the Linescan model, the system achieves an effective imaging area of 1 mm × 3 mm in 14 s and 1 mm × 4 mm in 12 s for the "O" and "Z" types, respectively. The proposed PAM systems have advantages in image resolution and control accuracy, indicating a significant potential in the field of facial angiography.

Pseudo-Spectral Time-Domain Method for Subsurface Imaging with the Lunar Regolith Penetrating Radar

Recently and successfully, the Chang’E-5 (CE-5) lander was launched on a mission to bring 1.731 kg of lunar soil back to Earth. To investigate various compositions of lunar regolith, we apply the Lunar Regolith Penetrating Radar (LRPR) as the same scientific payload installed on the CE-5 lander. Based on the high-accuracy imaging technique, we achieve subsurface imaging to process LRPR-measured data collected from the lunar-like exploration tests in our laboratory. In this paper, we propose the pseudo-spectral time-domain (PSTD) method as the underlying code to implement the reverse-time migration (RTM) method and restore the uncertain subsurface area. With the significant advantage of lower spatial sampling density, the PSTD-RTM method not only saves major computational resources, but also rapidly confirms the object prediction in the effective imaging area. To further analyze the LRPR measured data, we employ the spectrum window to remove high- and low-frequency noise, and thus improve imaging visibility to some extent. The imaging results in this paper can prove the reliability and efficiency of the PSTD-RTM method for subsurface discoveries in planetary exploration.

Frequency-domain imaging algorithm based on time-frequency-domain perturbation for maneuvering highly squinted FMCW-SAR

Serious range-azimuth coupling and spatial variability of imaging parameters limit the focusing depth of conventional synthetic aperture radar (SAR) imaging methods for maneuvering high-squint frequency modulated continuous wave -SAR. To expand the effective imaging area, an imaging method based on time-frequency-domain perturbation is proposed. First, the slant range model based on data recording parameters is optimized to remove Doppler frequency shift and secondary coupling caused by in-pulse movement. Then, the spatial variability of range cell migration (RCM) is corrected by constructing the time-domain perturbation function to achieve unified RCM correction. In azimuth processing, the linear spatial variability of the first- to third-order Doppler parameters and the second-order space variation of azimuth modulation frequency are removed by the time-frequency perturbation filtering functions. The focus quality of the nonscene center is effectively improved. Finally, the effectiveness of the algorithm is verified by both the simulation data and the measured data.

Horizontal-scanning attenuated total reflection terahertz imaging for biological tissues.

.Significance: Terahertz wave is a potential tool for biological tissues due to its noninvasiveness and high sensitivity to water. Attenuated total reflection (ATR) with the characteristics of high sensitivity and nondestruction has been applied for THz imaging.Aim: We aim to develop an imaging methodology to facilitate practical application of THz ATR imaging.Approach: We have demonstrated a horizontally scanning THz continuous wave ATR imaging system. The effective imaging area was as large as the prism imaging surface by optimizing the ATR prism, and the influence of secondary reflection can be well avoided. By taking the image resolution and stability of this system into consideration, the incident angle to the prism bottom was chosen to be 30 deg.Results: The image resolution of this system can be up to 400 and in horizontal and vertical directions, respectively. Furthermore, U87-glioma regions of mice brain tissues with different sizes and C6-glioma regions of rat brain tissues with relatively large size can be differentiated clearly from normal brain tissues by this imaging system. The volume and location of the tumor region shown in the THz images are similar to those visualized macroscopically in the corresponding visual and H&E-stained images.Conclusion: We indicate terahertz horizontal-scanning ATR imaging technique with large effective imaging area, and high resolution could be used as an alternative method for label-free and high-sensitivity imaging of biological tissues.

Fast charge exchange recombination spectroscopy on HuanLiu-2A tokamak.

A Fast Charge eXchange Recombination Spectroscopy (CXRS) diagnostic with eight radial channels has been implemented on a HuanLiu-2A (HL-2A) tokamak with a time resolution of up to 10 kHz monitoring helium II spectra or 1 kHz monitoring carbon VI spectra. The crucial aspects of the fast CXRS are to improve the spectral intensity and the acquisition frequency. The spectral intensity has been greatly enhanced by customized fiber bundles. The main boost in optimizing the acquisition frequency is achieved by binning more pixel rows of the charge coupled device (CCD) representing one radial channel and by reducing the effective image area of the CCD. Consequently, the sawtooth oscillations of ion temperature and rotation velocity are continuously observed for the first time in the HL-2A tokamak.

KT and azimuth sub‐region deramp‐based high‐squint SAR imaging algorithm mounted on manoeuvring platforms

Owing to the existence of high-order motion parameters and vertical velocity, severe range–azimuth coupling and two-dimensional spatial variability of the imaging parameters degrade the image quality of high-squint synthetic aperture radar (SAR) mounted on manoeuvring platforms. To accommodate these issues, a novel sub-aperture SAR imaging algorithm based on keystone transform (KT) and azimuth sub-region deramp is proposed. In the range dimension processing, a correction function is constructed based on the scene centre to realise non-spatial-variant range cell migration (RCM) correction and range–azimuth decoupling, and then the residual spatial-variant RCM is removed by the KT. In the azimuth dimension processing, considering the impact of the range distortion on the azimuth modulated phase, accurate analytical formula of the signal in the azimuth time domain is deduced. On this basis, a fast azimuth compression method based on the azimuth sub-region deramp is proposed, and the theoretical effective imaging area is analysed. The theoretical analysis and the simulations show that the proposed imaging algorithm has high computational efficiency and can effectively expand the imaging area of high-squint SAR mounted on manoeuvring platforms.

Design of longitudinal auto-tracking of the detector on X-ray in digital radiography

One algorithm is designed to implement longitudinal auto-tracking of the the detector on X-ray in the digital radiography system (DR) with manual collimator. In this study, when the longitudinal length of field of view (LFOV) on the detector is coincided with the longitudinal effective imaging size of the detector, the collimator half open angle ( Ψ), the maximum centric distance ( emax) between the center of X-ray field of view and the projection center of the focal spot, and the detector moving distance for auto-traking can be calculated automatically. When LFOV is smaller than the longitudinal effective imaging size of the detector by reducing Ψ, the emax can still be used to calculate the detector moving distance. Using this auto-tracking algorithm in DR with manual collimator, the tested results show that the X-ray projection is totally covered by the effective imaging area of the detector, although the center of the field of view is not aligned with the center of the effective imaging area of the detector. As a simple and low-cost design, the algorithm can be used for longitudinal auto-tracking of the detector on X-ray in the manual collimator DR.

A handheld microscope integrating photoacoustic microscopy and optical coherence tomography.

The combination of optical resolution photoacoustic microscopy (ORPAM) and optical coherence tomography (OCT) is capable of providing complementary imaging contrasts. Unfortunately, the miniaturization of ORPAM remains a major challenge in the development of a handheld dual-modality imaging microscope with OCT. Here, we report the design and evaluation of an integrated ORPAM and OCT imaging probe using a two-dimensional MEMS (micro-electro-mechanical-system)-based optical scanner. This microscope, weighting 35.4 g, has an ultracompact size of 65×30×18 mm3, and an effective imaging area of 2×2 mm2. The experimental lateral resolutions are 3.7 μm (ORPAM) and 5.6 μm (OCT), and the axial resolutions are measured as 120 μm (ORPAM) and 7.3 μm (OCT). Besides phantom and animal experiments, we carried out oral imaging of a healthy volunteer to show the clinical feasibility of this technique.

Effective histopathological image area reduction method for real-time applications

Effective histopathological image area reduction method for real-time applications

High-sensitivity attenuated total internal reflection continuous-wave terahertz imaging

We demonstrate an attenuated total internal reflection imaging system. The surface information of the sample on top of a prism can be acquired by two-dimensionally scanning this prism moving in the vertical plane with horizontally incident continuous terahertz waves at a fixed height. The principles and feasibility of this method are investigated. The effective imaging area on the prism, image resolution and polarization dependence of contrast enhancement and stability improvement are analyzed. Examples including solid agar, distilled water and porcine tissue are presented, demonstrating the method’s advantages of high sensitivity and simple sample preparation. The experimental and theoretical results consistently show that p-polarization contributes to enhanced image contrast and more stable intensity of the attenuated total internal reflected signal.

Spinning disk as a spatial light modulator for rapid infrared imaging

A novel spinning disk approach is reported, to achieve video-rate compressive imaging at infrared (IR) and terahertz (THz) frequencies. It uses a 200-mm-diameter circular stainless steel disk with a number of chemically etched 2-mm-diameter holes as a spatial light modulator (SLM). The authors demonstrate that this mechanical SLM is well suited for imaging at both optical and THz frequencies since the stainless steel is opaque to all optical and electromagnetic radiations while the holes are totally transparent. Using a single pair of IR emitter and receiver, the authors demonstrate that the system is capable of capturing a 96 × 96 video sequence at 10 frames/s. The achieved spatial resolution is better than 2 mm using the spinning disk where the diameter of the holes is 2 mm. The authors also present a key-frame extraction method based on this SLM disk, which allows us to capture the shape of a sample even when its size is larger than the effective imaging area of the system.

Toward Intraoperative Breast Endomicroscopy With a Novel Surface-Scanning Device.

New optical biopsy methods such as confocal endomicroscopy represent a promising tool for breast conserving surgery, allowing real-time assessment of tumor margins. However, it remains difficult to scan over a large surface area because of the small field-of-view. This paper presents a novel robotic instrument to perform automated scanning with a fiber bundle endomicroscope probe to expand the effective imaging area. The device uses a rigid concentric tube scanning mechanism to facilitate large-area mosaicking. It has a compact design with a diameter of 6mm, incorporating a central channel with a diameter of 3mm for passing through a fiber bundle probe. A bespoke bearing, an inflated balloon, and a passive linear structure are used to control image rotation and ensure consistent tool-tissue contact. Experimental results show that the device is able to scan a spiral trajectory over a large hemispherical surface. Detailed performance evaluation was performed and the bending angle ranges from -90° to 90° with high repeatability and minimal rotational hysteresis errors. The device has also been validated with breast phantom and ex vivo human breast tissue, demonstrating the potential clinical value of the system.

Imaging Functions of Quasi-Periodic Nanohole Array as an Ultra-Thin Planar Optical Lens

In this paper, the lensing functions and imaging abilities of a quasi-periodic nanohole array in a metal screen have been theoretically investigated and demonstrated. Such an optical binary mask with nanoholes designed in an aperiodic arrangement can function as an ultra-thin planar optical lens, imaging complex structures composed of multiple light sources at tens of wavelengths away from the lens surface. Via resolving two adjacent testing objects at different separations, the effective numerical aperture (N.A.) and the effective imaging area of the planar optical lens can be evaluated, mimicking the imaging function of a conventional lens with high N.A. Furthermore, by using the quasi-periodic nanohole array as an ultra-thin planar optical lens, important applications such as X-ray imaging and nano-optical circuits may be found in circumstances where conventional optical lenses cannot readily be applied.

High Vertical Resolution Full-Field Reflection-Type Three-Dimensional Angle-Deviation Microscope with Nonlinear Error Compensation

This study examines the use of reflectivity-height transformation in full-field angle-deviation microscopes (ADM). In such microscopes, two light intensity distribution images of a prism's total internal reflection and critical angle are obtained separately with two charge-coupled devices (CCDs), and are converted into a reflectivity profile point-to-point and then into angle of deviation matrix after the beam is reflected by the test sample; finally, the surface height of the sample is found through the triangular geometrical relationship. This method obtains the image through the effective imaging area of CCD. Once the two-dimensional (2D) image is obtained, the third dimension, height, is added to create a full-field 3D surface profile. Its conversion process is nonlinear; therefore, compensation must be made to reduce measurement errors. The optical magnification of high vertical resolution full-field 3D reflection-type ADM could reach >250 times, thus providing submicron measurements with nanometer vertical resolution and allowing for the simultaneous measurement of 2D and 3D images. Small defects on both transparent and nontransparent surfaces can be rapidly detected.

CMOS image sensor integrated with micro-LED and multielectrode arrays for the patterned photostimulation and multichannel recording of neuronal tissue

We developed a complementary metal oxide semiconductor (CMOS) integrated device for optogenetic applications. This device can interface via neuronal tissue with three functional modalities: imaging, optical stimulation and electrical recording. The CMOS image sensor was fabricated on 0.35 μm standard CMOS process with built-in control circuits for an on-chip blue light-emitting diode (LED) array. The effective imaging area was 2.0 × 1.8 mm². The pixel array was composed of 7.5 × 7.5 μm² 3-transistor active pixel sensors (APSs). The LED array had 10 × 8 micro-LEDs measuring 192 × 225 μm². We integrated the device with a commercial multichannel recording system to make electrical recordings.

A Novel Unified-Noise Algorithm for Iris Recognition

The iris identification as one of the most effective ways in biometrics identification, which obtain more and more attention in all walks of life to a wide range of applications, but the recognition of the quality and speed still exist noise interference such as eyelash, eyelid, and sampling flare. In the paper we put forward a method that unified noise used to between login iris and sample iris images aiming at the widespread adoption of matching method. Basing on this way, we can effectively reduce the noise interference and increase for identification of utilization as soon as possible. It is found that the method can be applied to reduce regional differences resulted from noise regional disunity errors, and make us to get more effective iris image area, especially in inferiorly non-aggressive iris image area. Our study Indicates the result of calculation iris matching has better effect in direct gray-level surface.

Practical performance evaluation of a 10k × 10k CCD for electron cryo-microscopy.

Electron cryo-microscopy (cryo-EM) images are commonly collected using either charge-coupled devices (CCD) or photographic film. Both film and the current generation of 16 megapixel (4k × 4k) CCD cameras have yielded high-resolution structures. Yet, despite the many advantages of CCD cameras, more than two times as many structures of biological macromolecules have been published in recent years using photographic film. The continued preference to film, especially for subnanometer-resolution structures, may be partially influenced by the finer sampling and larger effective specimen imaging area offered by film. Large format digital cameras may finally allow them to overtake film as the preferred detector for cryo-EM. We have evaluated a 111-megapixel (10k × 10k) CCD camera with a 9 μm pixel size. The spectral signal-to-noise ratios of low dose images of carbon film indicate that this detector is capable of providing signal up to at least 2/5 Nyquist frequency potentially retrievable for 3D reconstructions of biological specimens, resulting in more than double the effective specimen imaging area of existing 4k × 4k CCD cameras. We verified our estimates using frozen-hydrated ε15 bacteriophage as a biological test specimen with previously determined structure, yielding a ∼7 Å resolution single particle reconstruction from only 80 CCD frames. Finally, we explored the limits of current CCD technology by comparing the performance of this detector to various CCD cameras used for recording data yielding subnanometer resolution cryo-EM structures submitted to the electron microscopy data bank (http://www.emdatabank.org/).

Evaluation of a EMCCD Detector for Emission-Transmission Computed Tomography

A prototype electron multiplying charged coupled device (EMCCD) based gamma camera is evaluated for emission-transmission computed tomography. The detector has an 8.2times8.2 mm2 active sensor area with a 512times512 pixel array, and can be operated with a 3:1 fiber optic taper to expand the effective imaging area to approximately 25times25 mm2 for small animal studies. We demonstrate the possibility of operating the camera in either charge integrating or single photon counting mode for pinhole SPECT with 125I and 99mTc sources. In photon counting mode, we show that energy discrimination can be used to distinguish between these two sources for dual isotope imaging. X-ray CT images of phantoms are taken without a collimator to evaluate the quality of the camera for transmission imaging

The Sloan Digital Sky Survey Photometric Camera

We have constructed a large-format mosaic CCD camera for the Sloan Digital Sky Survey. The camera consists of two arrays, a photometric array that uses 30 2048 × 2048 SITe/Tektronix CCDs (24 μm pixels) with an effective imaging area of 720 cm2 and an astrometric array that uses 24 400 × 2048 CCDs with the same pixel size, which will allow us to tie bright astrometric standard stars to the objects imaged in the photometric camera. The instrument will be used to carry out photometry essentially simultaneously in five color bands spanning the range accessible to silicon detectors on the ground in the time-delay–and–integrate (TDI) scanning mode. The photometric detectors are arrayed in the focal plane in six columns of five chips each such that two scans cover a filled stripe 25 wide. This paper presents engineering and technical details of the camera.