Pinhole Edge Research Articles

A scanning focus nuclear microscope with multi-pinhole collimation

Microscopic nuclear imaging down to spatial resolutions of a few hundred microns can already be achieved using low-energy gamma emitters (e.g. 125I, ∼30 keV) and a basic single micro-pinhole gamma camera. This has been applied to in vivo mouse thyroid imaging, for example. For clinically used radionuclides such as 99mTc, this approach fails due to penetration of the higher-energy gamma photons through the pinhole edges. To overcome these resolution degradation effects, we propose a new imaging approach: scanning focus nuclear microscopy (SFNM). We assess SFNM using Monte Carlo simulations for clinically used isotopes. SFNM is based on the use of a 2D scanning stage with a focused multi-pinhole collimator containing 42 pinholes with narrow pinhole aperture opening angles to reduce photon penetration. All projections of different positions are used to iteratively reconstruct a three-dimensional image from which synthetic planar images are generated. SFNM imaging was tested using a digital Derenzo resolution phantom and a mouse ankle joint phantom containing 99mTc (140 keV). The planar images were compared with those obtained using a single-pinhole collimator, either with matched pinhole diameter or with matched sensitivity. The simulation results showed an achievable 99mTc image resolution of 0.04 mm and detailed 99mTc bone images of a mouse ankle with SFNM. SFNM has strong advantages over single-pinhole imaging in terms of spatial resolution.

Micromechanical approach to viscoelastic stress analysis of a pin-loaded hole in unidirectional laminated PMC

This paper aims to investigate the effect of viscoelastic behavior of polymer matrix of unidirectional fiber-reinforced laminated composite on stress distribution around the pin-loaded hole under tensile loading. The Laplace transform is used to prevent the integral form of matrix governing stress-strain relation. Applying a micromechanical model, all equilibrium equations for the fibers are written analytically in the Laplace domain. The numerical algorithm of Gaver–Stehfest is implemented, and the governing equations were solved at any given time to extract the concerned results in the time domain. The obtained results are validated against the Finite Element Method results obtained through ANSYS software. Moreover, a comparison of the results of this study at the time equal zero with elastic solutions of other references showed a good agreement. The results revealed that in the long term, the maximum tensile load in the intact fiber around the pinhole was enlarged and the tensile load in fibers far from the pinhole slightly was decreased. Moreover, the location of the maximum axial load that had occurred on pinhole edges was moved slightly toward the center over time.

Pulse energy limitation of high-power nanosecond lasers due to plasma production in spatial filters

For a neodymium glass laser, which is used to pump the parametric amplifier of the PEARL facility, we investigate the problem of filling the pinholes of vacuum spatial filters with plasma resulting from the ablation of the pinhole surface by laser radiation. The time of plasma expansion is measured and the causes of its appearance are determined, among which the main ones are the spherical aberrations of the lenses of spatial filters, which increase the intensity at the pinhole edges. With the total spherical aberration of the spatial filters, which lowers the Strehl number to 0.15, two nanosecond pulses with energies of 130 – 140 J, delayed relative to each other by 1.8 ns and freely passing through the final spatial filter, are generated on the PEARL facility.

High-resolution clustered pinhole 131Iodine SPECT imaging in mice

IntroductionHigh-resolution pre-clinical 131I SPECT can facilitate development of new radioiodine therapies for cancer. To this end, it is important to limit resolution-degrading effects of pinhole edge penetration by the high-energy γ-photons of iodine. Here we introduce, optimize and validate 131I SPECT performed with a dedicated high-energy clustered multi-pinhole collimator. MethodsA SPECT–CT system (VECTor/CT) with stationary gamma-detectors was equipped with a tungsten collimator with clustered pinholes. Images were reconstructed with pixel-based OSEM, using a dedicated 131I system matrix that models the distance- and energy-dependent resolution and sensitivity of each pinhole, as well as the intrinsic detector blurring and variable depth of interaction in the detector. The system performance was characterized with phantoms and in vivo static and dynamic 131I-NaI scans of mice. ResultsReconstructed image resolution reached 0.6mm, while quantitative accuracy measured with a 131I filled syringe reaches an accuracy of +3.6±3.5% of the gold standard value. In vivo mice scans illustrated a clear shape of the thyroid and biodistribution of 131I within the animal. Pharmacokinetics of 131I was assessed with 15-s time frames from the sequence of dynamic images and time–activity curves of 131I-NaI. ConclusionsHigh-resolution quantitative and fast dynamic 131I SPECT in mice is possible by means of a high-energy collimator and optimized system modeling. This enables analysis of 131I uptake even within small organs in mice, which can be highly valuable for development and optimization of targeted cancer therapies.

Influence of Small Defects Produced in Electrolytes during Manufacturing Processes on Operated SOFCs

To progress further social implementation, improvement of the durability and reliability are essential. One of the topics for mechanical durability is the evaluation of the effect of small defects in electrolyte. Small defects such as pinholes and unstructured pores in electrolytes layer could not be prevented in the case of electrode-supported type cells because its thickness is only several mm in these days. Through these defects, gas leakage between cathode and anode and the combustion of leaked fuel and air were considered to occur. In this study, we evaluate various influences caused by gas leakage such as thermal stress, anode re-oxidation using model cell. To evaluate such local phenomenon on operated SOFCs, the new stress evaluation method using micro Raman scattering spectroscopy has been adopted. The stress conditions evaluation method focuses on Raman spectra of samarium-doped ceria (SDC) which was often used as an interlayer. The stress condition of electrolyte can be calculated, considering the thermal stress between interlayer and electrolyte. There are several advantages in In-situ Raman scattering spectroscopy: 1) nondestructive, 2) contact-less, 3) high spatial resolution. Therefore, the method using micro Raman scattering spectroscopy can obtain the local stress conditions of SDC interlayer in SOFCs at operating conditions. In this method, the shift of F2g vibration mode peak of samarium-doped ceria (SDC) was used as a probe of stress conditions evaluation. Because the shift of Raman peak by stress change is not so drastic, e.g. 0.2 cm-1 / 100 MPa, the accuracy of Raman peak position is essential. SDC Raman spectra change by not only stress but also Sm concentration and temperature. By measuring temperature and Sm concentration dependence of SDC Raman spectra variations, the information about temperature and Sm concentration can be obtained in addition to stress on the measurement points. In this study, first, this method was applied to measuring the stress condition in SOFCs in operating conditions. Next, We tried to evaluate the effect of the pinhole in electrolyte under operating conditions by using this method. The local stress and temperature were measured. Additionally, to define the mechanism of the gas leak through small defect in electrolyte, the amount of gas leak through pinhole was measured by using gas chromatography. This method was applied to measuring the stress condition in two types of conventional anode supported type SOFC during operating condition. At R.T., the residual stress in electrolyte was a compression of about 400~500MPa. At elevated temperature, the residual stress decreases with increasing temperature, becoming a compression of about 100MPa. This results suggest that the internal stress in SOFCs is caused by thermal stress. During reduction, the internal stress changes to approximately zero. This relaxation stress could be caused by the reduction of NiO. These results showed that the stress evaluation method using micro Raman scattering spectroscopy can be applied to measuring the local stress condition in SOFCs under operating conditions. Before evaluate the stress around the small defect in electrolyte under operating conditions by using this method, We tried to define the mechanism of the gas leak through the pinhole in electrolyte by measuring the amount of gas leak through pinhole Pinholes (Φ150mm) were etched in electrolyte to simulate small defects, and actual gas leakage was evaluated under difference working pressure (0~100 Pa) between cathode side and anode side at R.T. The gas leak was constant value in difference working pressure. This result suggest that gas leak through electrolyte is caused by not pressure difference but also mutual gas diffusion. The change of stress conditions and temperature around the pinhole due to the change of gas leakage was measured during operation. After reduction, anode in pinhole was local oxidation state. This reasons was that air leak to anode by gas diffusion increase p(O2) in this area. Temperature around pinhole increase about 10K inside 100μm distance from pinhole edge by the combustion. The change of the stress around pinhole by the effect of leak gas was nearly zero. To take about 30MPa measurement error in Raman measurement into consideration, these stress caused by local oxidation and combustion were below 30MPa.

Theoretical and experimental study for shortening laser pulse width by pinhole plasma shutter

In this article, a theoretical model is presented to calculate the laser clipped pulse temporal width by the pinhole plasma shutter, and then the model results are compared with the experimental results of CO 2 laser clipped pulses by aluminum and copper pinhole plasma shutters. In this model, it is assumed that the laser clipped pulse width is approximately equal to the sum of the plasma formation time and the plasma propagation time in order to reach from pinhole edges to the pinhole center. Furthermore, we assume that the plasma formation time is approximately equal to the time for the surface temperature of pinhole metal plate to reach the boiling point by absorbing the laser pulse energy. Heat conduction equation is used to calculate the time of plasma formation, and Taylor-Sedov’s model is used to calculate the plasma propagation time to reach the pinhole center. By these assumptions, a relationship has been established between the laser clipped pulse width on the one hand, and thermo-dynamical and optical parameters of plasma shutter and the involved laser optical parameters on the other. Results of this model are in good agreement with experimental results.

Stress intensity factors of a corner crack emanating from a pinhole of a solid cylinder

This paper presents stress intensity factors (SIFs) and fatigue growth analyses of a corner crack emanating from a pinhole of a cylinder under cyclic tension. No such work has been reported in the literature. Stress intensity factors for different crack aspect ratios and pinhole sizes in different diameters of solid cylinder are presented. A larger SIF was found at the smaller crack size of a or c in a larger diameter of a pinhole of the smaller-diameter cylinder. Crack growths at the pinhole edge were found to be faster than those at the cylinder edge.

Laser irradiation effects on the CdTe/ZnTe quantum dot structure studied by Raman and AFM spectroscopy

Micro-Raman spectroscopy has been applied to investigate the impact of laser irradiation on semiconducting CdTe/ZnTe quantum dots (QDs) structures. A reference sample (without dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy technique on the p-type GaAs substrate. The Raman spectra have been recorded for different time of a laser exposure and for various laser powers. The spectra for both samples exhibit peak related to the localized longitudinal (LO) ZnTe phonon of a wavenumber equal to 210 cm−1. For the QD sample, a broad band corresponding to the LO CdTe phonon related to the QD-layer appears at a wavenumber of 160 cm−1. With increasing time of a laser beam exposure and laser power, the spectra get dominated by tellurium—related peaks appearing at wavenumbers around 120 cm−1 and 140 cm−1. Simultaneously, the ZnTe surface undergoes rising damage, with the formation of Te aggregates at the pinhole edge as reveal atomic force microscopy observations. Local temperature of irradiated region has been estimated from the anti-Stokes/Stokes ratio of the Te modes intensity and it was found to be close or exceeding ZnTe melting point. Thus, the laser damage can be explained by the ablation process.

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.

High-resolution tomography of positron emitters with clustered pinhole SPECT

State-of-the-art small-animal single photon emission computed tomography (SPECT) enables sub-half-mm resolution imaging of radio-labelled molecules. Due to severe photon penetration through pinhole edges, current multi-pinhole SPECT is not suitable for high-resolution imaging of photons with high energies, such as the annihilation photons emitted by positron emitting tracers (511 keV). To deal with this edge penetration, we introduce here clustered multi-pinhole SPECT (CMP): each pinhole in a cluster has a narrow opening angle to reduce photon penetration. Using simulations, CMP is compared with (i) a collimator with traditional pinholes that is currently used for sub-half-mm imaging of SPECT isotopes (U-SPECT-II), and (ii), like (i) but with collimator thickness adapted to image high-energy photons (traditional multi-pinhole SPECT, TMP). At 511 keV, U-SPECT-II is able to resolve the 0.9 mm rods of an iteratively reconstructed Jaszczak-like capillary hot rod phantom, and while TMP only leads to small improvements, CMP can resolve rods as small as 0.7 mm. Using a digital tumour phantom, we show that CMP resolves many details not assessable with standard USPECT-II and TMP collimators. Furthermore, CMP makes it possible to visualize uptake of positron emitting tracers in sub-compartments of a digital mouse striatal brain phantom. This may open up unique possibilities for analysing processes such as those underlying the function of neurotransmitter systems. Additional potential of CMP may include (i) the imaging of other high-energy single-photon emitters (e.g. I-131) and (ii) localized imaging of positron emitting tracers simultaneously with single photon emitters, with an even better resolution than coincidence PET.

Modeling of the Point Spread Function by Numerical Calculations in Single-Pinhole and Multipinhole SPECT Reconstruction

In conventional reconstruction of single photon emission computed tomography (SPECT) data acquired with a single-pinhole or multipinhole system, the point spread function (PSF) may be either approximated by some analytical equations or substituted by the sensitivity function, which is the integral of the PSF. We have developed a method to numerically calculate the PSF for a pinhole system in order to improve image resolution over a sensitivity-function-based method. The method calculates the probability of photon penetration through the pinhole edges using a ray-tracing approach. To calculate the transmission by the collimator plate along each ray, we trace the ray through the collimator by analytical calculations. The PSF is calculated for only one detector angle, and a Gaussian rotator is used to rotate the image grid for other detector angles in the iterative reconstruction. To evaluate our method, we measured the sensitivities of four keel-edged single-pinhole plates and scanned an ultramicro Derenzo phantom on a single-pinhole system and a five-pinhole system and performed two mouse bone scans on the five-pinhole system using the 140 keV photons of Tc-99m. The numerical calculations of sensitivities for the single-pinhole plates agreed well with the measurements. Results for both types of data scans showed that modeling of the PSF improved image resolution. In conclusion, we found that modeling of the PSF by numerical calculations increases the resolution of reconstruction for single-pinhole and multipinhole SPECT imaging.

Interfacial parameter analyses for sleeve-pin-shaft connections under axial and torsional cyclic loading using the finite element method

This study investigates the interfacial behaviour of the contact surfaces of the sleeve-pin-shaft connections under axial and torsional cyclic loading. Fatigue experiments for the connections have been performed in a previous study using a biaxial material testing system. The fretting fatigue cracks initiated at the pin-hole edge of the shafts were found to be the main cause of failure of the connections. In this work, the fretting wear parameters and cyclic stress/strain behaviour of the contact surfaces of the components are simulated using the elastic-plastic finite element method. Several representative interfacial parameters, such as contact pressure, slip displacement, and tangential stress along the pin-hole edge of the shaft are considered herein. The effect of the coefficient of friction between the contact surfaces on the stress/strain behaviour on the pin-hole edge is also investigated. These simulated results can be applied in the future to elucidate the complicated failure mechanism that results from interaction between the plain fatigue and fretting fatigue behaviours of the contact surfaces.

Photon penetration and scatter in micro-pinhole imaging: a Monte Carlo investigation

Pinhole SPECT is rapidly gaining popularity for imaging laboratory animals using gamma-emitting molecules. Penetration and scattering of gamma radiation in the pinhole edge material can account for a significant fraction of the total number of photons detected, particularly if the pinholes have small diameters. This study characterizes the effects of penetration and scatter with micro-pinholes made of lead, tungsten, gold and platinum. Monte Carlo simulations are performed for I-125 (27–35 keV) and Tc-99m (140 keV) point sources with pinhole diameters ranging from 50 to 500 µm. The simulations account for the effects of photo-electric interaction, Rayleigh scattering, Compton scattering, ionization, bremsstrahlung and electron multiple scattering. As a typical example, in the case of a Tc-99m point source and pinholes with a diameter of 300 µm in gold or platinum, approximately 55% of the photons detected resulted from penetration and approximately 3% from scatter. For pinhole diameters ranging from 100 to 500 µm, the penetration fraction for tungsten and lead was approx a factor of 1.0 to 1.6 higher and the scatter fraction was 1.0 to 1.8 times higher than in case of gold or platinum. Using I-125 instead of Tc-99m decreases the penetration fraction by a factor ranging from 3 to 11 and the scatter fraction by a factor ranging from 12 to 40. For all materials studied, the total amounts of penetrated and scattered photons changed approximately linearly with respect to the pinhole diameter.

Further evidence for a reversed crossing of foveal projections in schizophrenic vulnerability

Further evidence in support of the thesis developed in a previous article published in Medical Hypotheses (Sept. 2000) proposing that schizophrenic vulnerability might consist of the temporal instead of the nasal foveal projections crossing over in the chiasma opticum has been provided by an experiment in which pinholes are used to isolate foveally stimulated from peripherally stimulated vergence. By shifting the pinholes inwards or outwards a dilemma is created regarding the fusion of the edges of the two pinholes or of a single diode light seen at the inner or outer edges of the pinholes. It was revealed that schizophrenic patients never solved the dilemma in favour of what was represented on the temporal foveal halves while this was always the case in the control group. At best, the patients fusioned neither the diode light nor the pinhole edges but saw both double. An explanation is given as to how this disturbance might be based on the interchange of nasal and temporal foveal projections and might lead to the dissociation of the visual goals of the two eyes, as shown in a previous test. The cause of markers of schizophrenic vulnerability mentioned in literature, in particular saccaded SPEM, P50 response and hyperdopaminergia, is related to such an interchange and suggestions are made for further experiments. Finally, the difficulty of schizophrenic patients to distinguish between reality and illusion is attributed to a disconnection of spatial and object perception.

Uranium pinhole collimators for 511-keV photon SPECT imaging of small volumes

Depleted uranium (DU) pinhole collimators are evaluated for small-volume SPECT imaging of 511-keV gammas, with a view toward small-animal imaging. Tungsten (W) pinholes are examined for comparison. Line source measurements show planar full-width at half-maximum (FWHM) as low as 6.5 mm for a 1-mm DU pinhole, with SPECT system FWHM of 5.0 mm at 43-mm ROR and 6.7 mm at 69-mm ROR. Planar FWHM is smaller for DU than for W pinholes but is insensitive to aperture size for pinholes of 1-3 mm diameter at this energy for the collimators studied. These trends indicate penetration at pinhole edges, as confirmed by LSF shape and full-width at tenth-maximum trends. In SPECT scans of rod phantoms at 71-mm ROR, DU pinholes were only barely able to resolve cold rods as large as 4.7 mm (center-to-center spacing=2/spl times/diameter). For both F-18 alone and F-18 imaged along with Tc-99m, 3.9-mm hot rods were resolved. Tc-99m scans resolved 2.3- mm rods with F-18 present and 1.5-mm rods without F-18. DU pinhole SPECT at 511 keV does not currently match the spatial resolution of high-resolution positron emission tomography (PET) but is open to improvement and, unlike PET, is capable of simultaneous multiple-isotope acquisitions.

Uranium pinhole collimators for I-131 SPECT imaging

Pinhole apertures made of depleted uranium were evaluated for high-resolution SPECT brain tumor imaging of therapeutic doses (30-100 mCi) of intratumorally administered I-131 radiolabeled monoclonal antibodies. High resolution is required for imaging residual tumor tissue, although for therapeutic doses, high collimator sensitivity is less important. Resolution of uranium and tungsten pinhole apertures was compared in planar and SPECT images of I-131 sources. Planar sensitivity was studied on- and off-axis. On-axis planar resolution for uranium pinholes is higher than that of tungsten pinholes for all cases examined; full-width-half-max (EWHM) is narrower for a 3 mm uranium pinhole than for a 1 mm tungsten pinhole, indicating significantly lower penetration at pinhole edges for uranium than for tungsten. Collimator sensitivity is higher for tungsten than for uranium, which also indicates higher edge penetration for tungsten. On-axis SPECT (14.4 cm radius) scans also show better resolution for a 2 mm uranium pinhole (7.8 mm EWHM) than for a 2 mm tungsten pinhole (9.5 mm FWHM), Background radiation from a uranium collimator (102 cts/sec) is acceptably low compared to expected clinical count rates.

Investigation of the pin joints in composites by the moiré method

A method combining moire-fringe patterns with strain-gage measurements is applied to the analysis of strain distribution in a double-lap joint specimen under pin load. The specimens are crossplied and woven-fabric graphite/epoxy composites. Fiber orientations for both of the composites are 0 deg/90 deg, and ±45 deg to the load direction. The results indicate that the strain distributions in the specimen are greatly influenced by the fiber orientation. In this experiment, these specimens were collapsed at the pin-hole edge by the pin load. However, the failure load is not always dependent on the fiber orientation.

Scattering of low-energy electrons on micron-size pinholes

In exploring forces between charged particles and surfaces, we have sent a beam of low-energy (0.5–40 eV) electrons through two (laser drilled) micron-size pinholes in thin films of gold spaced 10 cm apart. Image forces associated with the solid around the second pinhole cause the beam to diverge into an angular distribution which is scanned with a movable slit and Channeltron detector. Distributions have widths which depend inversely on electron energy as expected from transit time considerations. The paraxial portion of the distribution appears to diverge as though from a weak negative electron lens. The impulse approximation for the radial component of the electron motion is used to derive a radial potential averaged along a line parallel to the pinhole axis. This potential approximately equals the expected value e/4x at x=10 Å from the pinhole edge but deviates from this function at greater distances. This deviation may be due to geometric effects, to the impulse collision model employed, or to geometric irregularities at the edge. The results are useful in estimating efficiencies of filters for charged aerosol collection.

<title>Ronchi Ruling Method for Measuring Gaussian Beam Diameter</title>

Ronchi rulings may be used for fast, accurate measurements of Gaussian beam diameters. In this paper, we present a theoretical analysis of the Ronchi measurement method. The major theoretical result is a very simple relationship between beam diameter and the measured parameters, P max and P min. The Ronchi method is then compared with the more conventional pinhole, slit, and knife edge methods. The major advantages of the Ronchi method are discussed, and some notes on the application of the method are given.

Use of image restoration and enhancement to improve x-ray pinhole camera resolution

Numerical image processing techniques are applied to the restoration of x-ray pinhole photographs of solid targets irradiated by intense relativistic electron beams. The numerical and analytic bases for image restoration are briefly described. An experimentally determined point-spread function for the pinhole camera is utilized to eliminate the effects of high-energy x-ray degradation of pinhole resolution. It is shown that penetration by hard x rays from filtered spectra through the pinhole edges can lead to apparent broadening of the electron-beam pinch on high-Z targets. Elimination of x-ray shine-through also permits determination of photon intensity from high-Z target ablation products, and improves spatial resolution of the x-ray source.