Detector Pinhole Research Articles

Resolution and signal-to-noise ratio improvement in confocal fluorescence microscopy using array detection and maximum-likelihood processing

Confocal fluorescence microscopy (CFM) is widely used in biological sciences because of its enhanced 3D resolution that allows image sectioning and removal of out-of-focus blur. This is achieved by rejection of the light outside a detection pinhole in a plane confocal with the illuminated object. In this paper, an alternative detection arrangement is examined in which the entire detection/image plane is recorded using an array detector rather than a pinhole detector. Using this recorded data an attempt is then made to recover the object from the whole set of recorded photon array data; in this paper maximum-likelihood estimation has been applied. The recovered object estimates are shown (through computer simulation) to have good resolution, image sectioning and signal-to-noise ratio compared with conventional pinhole CFM images.

The Airyscan detector from ZEISS: confocal imaging with improved signal-to-noise ratio and super-resolution

With Airyscan, ZEISS introduced a new detector concept for confocal laser-scanning microscopy (LSM). Whereas traditional LSM designs use a combination of pinhole and single-point detectors, Airyscan is a 32-channel gallium arsenide phosphide photomultiplier tube (GaAsP-PMT) area detector that collects a pinhole-plane image at every scan position. Each detector element functions as a single, very small pinhole. Knowledge about the beam path and the spatial distribution of each detector channel enables very light-efficient imaging with improved resolution and signal-to-noise ratio.

Transverse profile of the electron beam for the RHIC electron lenses

The transverse profile of the electron beam plays a very important role in assuring the success of the electron lens beam–beam compensation, as well as its application in space charge compensation. To compensate for the beam–beam effect in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, we recently installed and commissioned two electron lenses. In this paper, we describe, via theory and simulations using the code Parmela, the evolution of the density of the electron beam with space charge within an electron lens from the gun to the main solenoid. Our theoretical analysis shows that the change in the beam transverse density is dominated by the effects of the space charge induced longitudinal velocity reduction, not by those of transverse Coulomb collisions. We detail the transverse profile of RHIC electron-lens beam, measured via the YAG screen and pinhole detector, and also describe its profile that we assessed from the signal of the electron-backscatter detector (eBSD) via scanning the electron beam with respect to the RHIC beam. We verified, in simulations and experiments, that the distribution of the transverse electron beam is Gaussian throughout its propagation in the RHIC electron lens.

Chromatic confocal matrix sensor with actuated pinhole arrays.

We present two versions of a chromatic confocal matrix sensor for the snapshot acquisition of three-dimensional objects. The first version contains separate illumination and detection pinhole arrays, while the second version uses a single pinhole array in double pass. The discrete lateral measurement points defined by the illumination and detection pinhole arrays are evaluated in parallel with a hyperspectral detection module. As this approach enables the spectrometric evaluation of all lateral channels, multilayer objects can be analyzed. To increase the lateral resolution the pinhole arrays are moved by micromechanical actuators. The paper includes a quantitative evaluation of the chromatic confocal module and proof-of-principle experiments with the full sensor system.

Design, optimization and performance of source and detector collimators for gamma-ray scanning of a lab-scale distillation column

When using source and detector collimators for gamma ray column scanning, it is important to obtain an acceptable density profile quality. This paper consists of two main works. The first is devoted to describing the designs used to optimize the source and detector collimators for a lab-scale distillation column, and the second is devoted to investigating the effect of designed collimators on the quality of the density profiles obtained using the gamma scanning technique. Simulations using the MCNP4C Monte Carlo code were performed to model the collimators and obtain the density profiles. The source and detector collimator designs were developed for a cylindrical volume source with the energy of 0.662MeV and 1in.×1in. NaI, respectively. The pinhole and panoramic collimator designs and the pinhole and quartic collimator designs were considered for the source and the detector, respectively. The source container, with an opening angle of 60°, has the capability of substituting the collimator for high resolution, general and high sensitivity purposes. The pinhole collimator parameters for the source that were obtained were generally quite coarse and were 1.2cm in diameter and 4cm in length. Additionally, the detector pinhole collimator thickness and length obtained were 4cm and 5cm, respectively. Using the semi-quartic collimator for the detector, the weight of required lead was reduced by over 33% compared with the pinhole collimator.The simulation results of the column scanning in abnormal operation condition have been validated by experimental measurement results. The obtained results from scans demonstrated that the optimized panoramic source collimator and semi-quartic detector collimator in this study could help us to obtain an acceptable density profile quality in total count approach.

Spatial coherence analysis for optical scanning holography.

In optical scanning holography (OSH), the system can be operated in coherent mode by using a pinhole detector, or in incoherent mode by using a spatially integrating detector. In the coherent mode, the three-dimensional (3D) amplitude transparency of an object is recorded and thus the phase of the object can be retrieved. On the other hand, it is the 3D intensity transparency of the object recorded in the incoherent mode and thus the speckle can be suppressed. OSH in both coherence modes has been well investigated. However, there is no discussion on the case between the coherent mode and incoherent mode, namely, the partial-coherent mode. In this paper, we derived for the first time, to the best of our knowledge, the formula of OSH in various modes of coherence. We found the detector in OSH plays the role of a kind of filter for the field. The retrieved amplitude transparency of the object is thus nonlinearly processed by the mask function of the detector. Consequently, the reconstructed image cannot benefit from the implementation of the partial-coherent mode. On the contrary, significant artifacts usually appear among the reconstructed image and thus the image quality degrades.

Spectral characteristics of chromatic confocal imaging systems.

We present signal-generation models for chromatic confocal imaging systems with illumination and detection pinholes of finite size: a collinear model that considers neither aberrations nor diffraction effects, a geometrical model that accounts for aberrations, and a wave optical model covering both aberrations and diffraction effects. These models are aimed at describing the spectral response of multipoint sensor systems with field-dependent aberrations and vignetting effects. They are suitable for single- and double-pass systems with either diffusely or specularly reflecting surfaces under test. We show experimental results to verify our models.

A hardware investigation of robotic SPECT for functional and molecular imaging onboard radiation therapy systems.

To construct a robotic SPECT system and to demonstrate its capability to image a thorax phantom on a radiation therapy flat-top couch, as a step toward onboard functional and molecular imaging in radiation therapy. A robotic SPECT imaging system was constructed utilizing a gamma camera detector (Digirad 2020tc) and a robot (KUKA KR150 L110 robot). An imaging study was performed with a phantom (PET CT Phantom(TM)), which includes five spheres of 10, 13, 17, 22, and 28 mm diameters. The phantom was placed on a flat-top couch. SPECT projections were acquired either with a parallel-hole collimator or a single-pinhole collimator, both without background in the phantom and with background at 1/10th the sphere activity concentration. The imaging trajectories of parallel-hole and pinhole collimated detectors spanned 180° and 228°, respectively. The pinhole detector viewed an off-centered spherical common volume which encompassed the 28 and 22 mm spheres. The common volume for parallel-hole system was centered at the phantom which encompassed all five spheres in the phantom. The maneuverability of the robotic system was tested by navigating the detector to trace the phantom and flat-top table while avoiding collision and maintaining the closest possible proximity to the common volume. The robot base and tool coordinates were used for image reconstruction. The robotic SPECT system was able to maneuver parallel-hole and pinhole collimated SPECT detectors in close proximity to the phantom, minimizing impact of the flat-top couch on detector radius of rotation. Without background, all five spheres were visible in the reconstructed parallel-hole image, while four spheres, all except the smallest one, were visible in the reconstructed pinhole image. With background, three spheres of 17, 22, and 28 mm diameters were readily observed with the parallel-hole imaging, and the targeted spheres (22 and 28 mm diameters) were readily observed in the pinhole region-of-interest imaging. Onboard SPECT could be achieved by a robot maneuvering a SPECT detector about patients in position for radiation therapy on a flat-top couch. The robot inherent coordinate frames could be an effective means to estimate detector pose for use in SPECT image reconstruction.

Influences of Detection Pinhole and Sample Flow on Thermal Lens Detection in Microfluidic Systems

Thermal lens microscopy (TLM), due to its high temporal ( $${\sim }\mathrm{ms}$$ ) and spatial resolution ( $${\sim }\upmu \mathrm{m}$$ ), has been coupled to lab-on-chip chemistry for detection of a variety of compounds in chemical or biological fields. Due to the very short optical path length (usually below 100 $$\upmu \mathrm{m}$$ ) in a microchip, the sensitivity of TLM is unfortunately still 10 to 100 times lower than conventional TLS with 1 cm sample length. Optimization of the TLM optical configuration was made with respect to different pinhole aperture-to-beam size ratios for the best signal-to-noise ratio. In the static mode, the instrumental noise comes mainly from the shot noise of the probe beam when the chopper frequency is over 1 kHz or from the flicker noise of the probe beam at low frequencies. In the flowing mode, the flow-induced noise becomes dominant when the flow rate is high. At a given flow rate, fluids with a higher density and/or a higher viscosity will cause larger flow-induced noise. As an application, a combined microfluidic flow injection analysis ( $$\upmu \mathrm{FIA}$$ )–TLM device was developed for rapid determination of pollutants by colorimetric reactions. Hexavalent chromium [Cr(VI)] was measured as a model analyte. Analytical signals for 12 sample injections in 1 min have been recorded by the $${\upmu }$$ FIA–TLM. For injections of sub- $$\upmu $$ L samples into the microfluidic stream in a $$50\,\upmu \mathrm{m}$$ deep microchannel, a limit of detection of $$4\,\mathrm{ng}{\cdot }\mathrm{mL}^{-1}$$ was achieved for Cr(VI) in water at 60 mW excitation power.

SU‐E‐I‐79: Effect of Number of Pinholes in Onboard Robotic Multi‐Pinhole SPECT System

Purpose:To study the effect of number of pinholes for a novel Single Photon Emission Computed Tomography (SPECT) system for onboard molecular and functional imaging.Methods:Comparison studies were performed using simulation for the 49‐pinhole SPECT system and a series of reductions in number of pinholes. Trajectories about the breast of a supine patient were considered. Minimum distances, radii of rotation (RORs), were determined by requirements to fully view the region of interest (ROI) and to avoid collision between the detector and the patient. Reductions in RORs translate into improvements in sensitivity. Starting from the 49‐pinhole system, pinholes were removed pod by pod. The furthest two end pods in the Sup‐Inf direction were removed first for their higher likelihood of alleviating the collision avoidance criteria. After iterating through different combinations of pinhole pods, and selecting three combinations, the corresponding RORs were used to analytically calculate sensitivities.Results:Based on the Methods procedure, 3 combination of pods removal were identified: 1) Superior peripheral pod 2) Inferior peripheral pod 3) both pods. RORs were reduced at only one multi‐pinhole stop. Analytic calculation showed that sensitivities were reduced from 0.032 for the 49‐pinhole system to 0.028 for 42‐pinhole and to 0.023 for 39‐pinhole system respectively. The sensitivity per pinhole detector was approximately the same for all three cases.Conclusion:For the trajectories considered, only minimal improvements in RORs were identified by removing pinhole pods. Consequently, sensitivities decreased in proportion to the number of pinholes. Studies of other anatomical sites are needed to determine if in some cases sensitivity per pinhole can be improved by removing some pinholes.PHS/NIH/NCI grant R21‐CA156390‐01A1

The electron lens test bench for the relativistic heavy ion collider at Brookhaven National Laboratory

To compensate for the beam–beam effects from the proton–proton interactions at the two interaction points IP6 and IP8 in the Relativistic Heavy Ion Collider (RHIC), we are constructing two electron lenses (e-lenses) that we plan to install in the interaction region IR10. Before installing them, the electron gun, collector, instrumentation were tested and the electron beam properties were qualified on an electron lens test bench. We will present the test results and discuss our measurement of the electron beam current and of the electron gun perveance. We achieved a maximum current of 1A with 5kV energy for both the pulsed- and the DC-beam (which is a long turn-by-turn pulse beam). We measured beam transverse profiles with an yttrium aluminum garnet (YAG) screen and pinhole detector, and compared those to simulated beam profiles. Measurements of the pulsed electron beam stability were obtained by measuring the modulator voltage.

Laplacian Erosion: An Image Deblurring Technique for Multi-Plane Gamma-Cameras

Laplacian Erosion, an image deblurring technique for multi-plane Gamma-cameras, has been developed and tested for planar imaging using a GEANT4 Monte Carlo model of the Pixelated Emission Detector for RadioisOtopes (PEDRO) as a test platform. A contrast and Derenzo-like phantom composed of 125I were both employed to investigate the dependence of detection plane and pinhole geometry on the performance of Laplacian Erosion. Three different pinhole geometries were tested. It was found that, for the test system, the performance of Laplacian Erosion was inversely proportional to the detection plane offset, and directly proportional to the pinhole diameter. All tested pinhole geometries saw a reduction in the level of image blurring associated with the pinhole geometry. However, the reduction in image blurring came at the cost of signal to noise ratio in the image. The application of Laplacian Erosion was shown to reduce the level of image blurring associated with pinhole geometry and improve recovered image quality in multi-plane Gamma-cameras for the targeted radiotracer 125I.

A complete and computationally efficient numerical model of aplanatic solid immersion lens scanning microscope

This paper presents a computational model for modeling an aplanatic solid immersion lens scanning microscope. The scanning microscope model consists of three subsystems, each of which can be computed as a separate system, connected to the preceding or succeeding subsystem through the input/output only. Numerical techniques are used to enhance the computational efficiency of each subsystem. A distinct merit of the proposed model is that it can be used to simulate imaging results for diverse setups of the scanning microscope, like various polarizations, numerical aperture, and different detector pinhole sizes. It allows the study and analysis of both theoretical aspects like achievable resolution, and practical aspects like expected images for different object patterns and experimental setups. Further, due to its computational efficiency, diverse large scale structures can be easily simulated in scanning microscope and good experimental approaches determined before indulging into the time consuming and costly process of experimentation.

Strength and adhesion properties of acrylic polyol‐epoxy polyol resin protective coating on mild steel substrate

PurposeThe purpose of this paper is to improve the strength and adhesion properties of modified acrylic polyol resin using epoxy polyol resin (DEGBA).Design/methodology/approachThe hybrid systems were prepared by blending acrylic resin with epoxy polyol resin (Diglycidyl Ether of Bisphenol‐A, DGEBA) and polyisocyanate resin as hardener in various weight ratios with xylene as a solvent. The samples were applied on the pre‐treated cold rolled mild steel panels. The mechanical property of the blend has been evaluated using rapid impact tester (Sheen 806/40) and adhesion tester (Sheen Cross‐Hatch 750). Intended panels were checked for cracks using Dino‐Lite and Pinhole detectors (Elcometer 270/4). Crossed panels were observed for damages using digital polarized microscope (Dino‐Lite, AM413ZT). The thermal properties were studied using thermal analysis system (TGA TA‐Q500, DSC TA‐Q200).FindingsThe modification of acrylic polyol resins using DGEBA showed significant improvement of toughness compared to pure acrylic polyol resins. The blending systems with 10 wt percent of DGEBA and 90 wt percent of acrylic resin showed good adhesion and impact resistance properties on mild steel substrate.Research limitations/implicationsThe hybrid coating system has contributed to the basic conceptual understanding of the corrosion protection property, focusing mainly on recent research available.Practical implicationsThe blending method provided a simple and practical solution to improve the toughness of acrylic polyol resins.Originality/valueThe method for enhanced toughness of cured acrylic was novel and functionality of coating critically depends on adhesion between the coatings and underlying metal substrate.

Overview of Live‐Cell Imaging: Requirements and Methods Used

Overview of Live‐Cell Imaging: Requirements and Methods Used

Optimal detection pinhole for lowering speckle noise while maintaining adequate optical sectioning in confocal reflectance microscopes

Coherent speckle influences the resulting image when narrow spectral line-width and single spatial mode illumination are used, though these are the same light-source properties that provide the best radiance-to-cost ratio. However, a suitable size of the detection pinhole can be chosen to maintain adequate optical sectioning while making the probability density of the speckle noise more normal and reducing its effect. The result is a qualitatively better image with improved contrast, which is easier to read. With theoretical statistics and experimental results, we show that the detection pinhole size is a fundamental parameter for designing imaging systems for use in turbid media.

Two-photon fluorescence microscopy signal formation in highly scattering media: theoretical and numerical simulation

Using the radiative transfer theory and Monte Carlo simulations, we analyse the effect of scattering in a medium and of the size of the detector pinhole on the formation of the fluorescent signal in standard two-photon fluorescence microscopy (TPFM) systems. The theoretical analysis is based on a small-angle diffusion approximation of the radiative transfer equation, adapted to calculate the propagation of focused infrared radiation in media similar to the biological tissues in their optical properties. The accuracy of the model is evaluated by comparing the calculated excitation intensity in a highly scattering medium with the results of Monte Carlo simulations. To simulate a tightly focused Gaussian beam by the Monte Carlo method, the so called 'ray-optics' approach that correctly takes into account the finite size and shape of the beam waist is applied. It is shown that in the combined confocal and two-photon scanning microscopy systems not equipped with an external 'nondescanned' detector, the scattering significantly affects both the nonlinear excitation efficiency in the medium and the fluorescence collection efficiency of the system. In such systems, the rate of the useful TPFM signal in-depth decay is 1.5 — 2 times higher than in systems equipped with a 'nondescanned' detector.

Enhanced background rejection in thick tissue using focal modulation microscopy with quadrant apertures

Image formation in focal modulation microscopy using quadrant apertures (QFMM) is presented. The spatial resolution is discussed: compared with confocal microscopy, QFMM can simultaneously enhance the axial and transverse resolution. In contrast to focal modulation microscopy using D-shaped apertures (DFMM), QFMM can maintain x–y symmetry of spatial resolution, thus causing less confusion in imaging interpretation. The capability of background rejection is investigated, showing QFMM has the potential to increase imaging penetration depth. The signal level is also analyzed, indicating that the preferred detector pinhole radius is greater than for DFMM, resulting in a higher signal level.

Projection Process Modelling for Iterative Reconstruction of Pinhole SPECT

In iterative reconstruction of pinhole SPECT data, the forward and back projection processes are often performed using the ray tracing method. Ray tracing is computationally efficient, but it has the drawback of poor reconstruction quality due to the missing voxel effect and textural artefacts. In this paper, the pinhole projection process was modelled starting from consideration of all the main factors affecting pinhole projection, such as voxel shape, penetration of the pinhole edges and detector response. Next, approximations were made to reduce the computational speed and the effect of the approximations on reconstructed image accuracy was evaluated in simulation and phantom experiments and compared with the ray tracing algorithm. When used in conjunction with the ML-EM algorithm, the proposed model improved reconstructed image accuracy compared with the ray tracing method and achieved comparable computational efficiency. Therefore, the proposed projection model is a practical alternative to the ray tracing algorithm for pinhole SPECT reconstruction.

X-ray fluorescence computed tomography (XFCT) imaging of gold nanoparticle-loaded objects using 110 kVp x-rays

A conventional x-ray fluorescence computed tomography (XFCT) technique requires monochromatic synchrotron x-rays to simultaneously determine the spatial distribution and concentration of various elements such as metals in a sample. However, the synchrotron-based XFCT technique appears to be unsuitable for in vivo imaging under a typical laboratory setting. In this study we demonstrated, for the first time to our knowledge, the possibility of performing XFCT imaging of a small animal-sized object containing gold nanoparticles (GNPs) at relatively low concentrations using polychromatic diagnostic energy range x-rays. Specifically, we created a phantom made of polymethyl methacrylate plastic containing two cylindrical columns filled with saline solution at 1 and 2 wt% GNPs, respectively, mimicking tumors/organs within a small animal. XFCT scanning of the phantom was then performed using microfocus 110 kVp x-ray beam and cadmium telluride (CdTe) x-ray detector under a pencil beam geometry after proper filtering of the x-ray beam and collimation of the detector. The reconstructed images clearly identified the locations of the two GNP-filled columns with different contrast levels directly proportional to gold concentration levels. On the other hand, the current pencil-beam implementation of XFCT is not yet practical for routine in vivo imaging tasks with GNPs, especially in terms of scanning time. Nevertheless, with the use of multiple detectors and a limited number of projections, it may still be used to image some objects smaller than the current phantom size. The current investigation suggests several modification strategies of the current XFCT setup, such as the adoption of the quasi-monochromatic cone/fan x-ray beam and XFCT-specific spatial filters or pinhole detector collimators, in order to establish the ultimate feasibility of a bench-top XFCT system for GNP-based preclinical molecular imaging applications.