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Purpose: Recently, a multipinhole collimator with inserts that have both rectangular apertures and rectangular fields of view (FOVs) has been proposed for SPECT imaging since it can tile the projection onto the detector efficiently and the FOVs in transverse and axial directions become separable. The purpose of this study is to investigate the image properties of rectangular-aperture pinholes with submillimeter apertures sizes. Methods: In this work, the authors have conducted sensitivity and FOV experiments for 18 replicates of a prototype insert fabricated in platinum/iridium (Pt/Ir) alloy with submillimeter square-apertures. A sinqü fit to the experimental sensitivity has been performed for these inserts. For the FOV measurement, the authors have proposed a new formula to calculate the projection intensity of a flood image on the detector, taking into account the penumbra effect. By fitting this formula to the measured projection data, the authors obtained the acceptance angles. Results: The mean (standard deviation) of fitted sensitivity exponents q and effective edge lengths we were, respectively, 10.8 (1.8) and 0.38 mm (0.02 mm), which were close to the values, 7.84 and 0.396 mm, obtained from Monte Carlo calculations using the parameters of the designed inserts. For the FOV measurement, the mean (standard deviation) of the transverse and axial acceptances were 35.0 (1.2°) and 30.5° (1.6°), which are in good agreement with the designed values (34.3° and 29.9°). Conclusions: These results showed that the physical properties of the fabricated inserts with submillimeter aperture size matched our design well. [ABSTRACT FROM AUTHOR]

Multi-pinhole collimators are often used in pre-clinical SPECT systems because they have a better resolution-sensitivity tradeoff than parallel hole collimators when imaging small objects. Most multi-pinhole collimators are designed to allow no or only a limited amount of overlap between the different pinhole projections because the ambiguity introduced by multiplexing pinholes can result in artifacts. The origin of these artifacts is still not fully understood, but previous research has already shown that data incompleteness could be part of the explanation. Therefore, we developed a method to investigate data completeness in multiplexing multi-pinhole systems and showed that a certain activity distribution can be successfully reconstructed when the nonmultiplexed data is complete or when the overlap can be sufficiently de-multiplexed. We validated this method using computer simulated phantom data of different multiplexing systems. We also studied contrast-to-noise and nonprewhitening matched filter signal-to-noise ratio (NPW-SNR) to compare the image quality in a single pinhole system with multiplexing systems. We found that our method can indeed be used to evaluate data completeness in multiplexing systems and found no artifacts in the systems that had complete data. Sensitivity increased significantly with multiplexing but we found only small, nonsignificant differences in contrast-to-noise ratio. However, the NPW-SNR did slightly improve in the multiplexing setups. We conclude that more multiplexing does not necessarily result in more artifacts and that even a high amount of multiplexing can still result in artifact-free images if the nonmultiplexed data is complete or when the overlap can be sufficiently de-multiplexed. [ABSTRACT FROM PUBLISHER]

Background Measurements of refractive errors through subjective or automated refraction are not always possible in rapid assessment studies and community vision screening programs; however, measurements of vision with habitual correction and with a pinhole can easily be made. Although improvements in vision with a pinhole are assumed to mean that a refractive error is present, no studies have investigated the magnitude of improvement in vision with pinhole that is predictive of refractive error. The aim was to measure the sensitivity and specificity of 'vision improvement with pinhole' in predicting the presence of refractive error in a community setting. Methods Vision and vision with pinhole were measured using a log MAR chart for 488 of 582 individuals aged 15 to 50 years. Refractive errors were measured using non-cycloplegic autorefraction and subjective refraction. The presence of refractive error was defined using spherical equivalent refraction ( SER) at two levels: SER greater than ± 0.50 D sphere ( DS) and SER greater than ±1.00 DS. Three definitions for significant improvement in vision with a pinhole were used: 1. Presenting vision less than 6/12 and improving to 6/12 or better, 2. Improvement in vision of more than one log MAR line and 3. Improvement in vision of more than two log MAR lines. Results For refractive error defined as spherical equivalent refraction greater than ± 0.50 DS, the sensitivities and specificities for the pinhole test predicting the presence of refractive error were 83.9 per cent (95% CI: 74.5 to 90.9) and 98.8 per cent (95% CI: 97.1 to 99.6), respectively for definition 1. Definition 2 had a sensitivity 89.7 per cent (95% CI: 81.3 to 95.2) and specificity 88.0 per cent (95% CI: 4.4 to 91.0). Definition 3 had a sensitivity of 75.9 per cent (95% CI: 65.5 to 84.4) and specificity of 97.8 per cent (95% CI: 95.8 to 99.0). Similar results were found with spherical equivalent refraction greater than ±1.00 DS, when tested against the three pinhole-based definitions. Conclusion Refractive error definitions based on improvement in vision with the pinhole shows good sensitivity and specificity at predicting the presence of significant refractive errors. These definitions can be used in rapid assessment surveys and community-based vision screenings. [ABSTRACT FROM AUTHOR]

Peak power density stability and beam-wander precision of probe laser are important factors affecting the inspection results in the precision thingilm optical measurements. Pinholes are frequently used as a spatial filter in the optical inspection system. In this work, five different diameters of pinhole are investigated experimentally. It is found that pinhole diameter of 0.3 mm is considered to be a promising candidate for mounting in front of probe laser for silicon thin-film optical inspection due to better peak power density stability and better beam-wander precision. [ABSTRACT FROM AUTHOR]

Low sensitivity can become a major problem when very small pinholes are used in SPECT imaging. Although a larger pinhole aperture will improve the sensitivity, this will be at the cost of the spatial resolution. With a view to improving the resolution–sensitivity trade-off, this paper explores an iterative reconstruction algorithm that models the pinhole aperture based on multi-ray projections. This new implementation was validated using simulated data and phantom experiments. Two approaches were investigated. Firstly, the pinhole aperture was modelled in both the forward and the back projector. Secondly, the dual matrix implementation was investigated by modelling the pinhole aperture only in the forward projector. The systematic error, the full-width at half-maximum (FWHM) and the statistical error were quantified using the simulated data. Experimental phantom data were acquired for visual comparison with the reconstructions obtained from the simulated data. For a predefined number of iterations, the systematic error, the FWHM and the statistical error could be decreased when the pinhole aperture was modelled during iterative reconstruction. For a fixed, predefined statistical error of ±10%, smaller systematic errors and smaller FWHM were obtained when modelling the pinhole opening. When the dual matrix implementation was used, equivalent results could be obtained as when modelling the pinhole opening in both the forward and the back projector. The multi-ray method to accomplish resolution recovery during the reconstruction of pinhole SPECT projection images offers a better trade-off between spatial resolution and noise compared with a reconstruction which does not model the pinhole aperture. [ABSTRACT FROM AUTHOR]

Breast SPECT imaging with pinhole collimation provides high resolution and sensitivity when the pinhole aperture is in close proximity to the breast. In this study we used clinical count density scans to analyze quantitatively the effects of three acquisition geometries. A Trionix clinical scanner was used with rotation range limited to 180 degrees to simulat the presence of a torso. An isolated breast phantom containing two spherical lesions was mounted on a tiltable platform attached to the patient bed. The orbits were: A) single half-circular orbit (single HCO); B) three parallel half circles separated axially (triple parallel HCO); and C) three half circles with the plane of rotation for two half circles tilted +30 and -30 degrees relative to the middle (triple tilted HCO). Multiple scans were taken for all orbits to perform statistical analysis. ML-EM was used for reconstruction. Our analysis shows that for the central lesion, orbits ‘B’ and ‘C’ yield 31% and 28% higher peak contrast than orbit ‘A’. For the edge lesion, orbit ‘C’ gives a 55% higher peak contrast than ‘A’ and 70% higher than ‘B’. Signal-to-noise ratios are dependent on the lesion location. The contrast analysis suggests that triple half-circular orbits are superior to the single half-circular orbit, especially, when two of the circles are tilted so that a larger part of the breast volume stays in the field of view during acquisition. [ABSTRACT FROM AUTHOR]

Pinhole SPECT is sensitive to alignment and calibration. For circular orbits, it is typically assumed that the radius of rotation (ROR) is constant. Uncompensated deviation in the ROR from a constant has the potential to worsen resolution. Herein, we describe a method for determining the ROR as a function of gantry angle. This method uses a laser to serve as a reference line and a laser target mounted to the pinhole collimator to measure position. The target rotates with the collimator and is read-out at multiple angles. The two-dimensional read-out values are used to calculate the ROR as a function of angle. Experimental radionuclide SPECT projection data were acquired. The projection data were reconstructed using the angular-dependent correction and using an average ROR. The results indicate that it is difficult to distinguish the effect of this correction when the amplitude is less than about 0.5 mm. However, the correction is very pronounced for an amplitude of about 1 mm. [ABSTRACT FROM AUTHOR]