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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]

In multi-pinhole SPECT, overlapping the projections from different pinholes has been used to increase sensitivity. However, the prevailing view is that the overall quality of the reconstructed image is not improved by the overlaps in the projections. It is often stated in literatures that overlaps introduce ambiguous information, which can lead to nonuniqueness of solution for the inverse problem, and thus artifacts are introduced in the reconstructed image. On the other hand, contrary to the prevailing view, a recent study on slit-slat collimators shows that artifacts can be removed with the “help” of an extra complete nonoverlapped projection data set. In this paper, two types of artifact-free projection overlaps are defined in general, and the criteria for designing artifact-free multi-pinhole systems with overlaps are proposed. It is shown that once the criteria are satisfied, the solution of the inverse problem is unique, and thus no artifact is expected in the reconstructed image. Via extensive simulation study, various artifact-free overlapping multi-pinhole systems are designed and validated. It is shown that overlaps in the artifact-free systems can improve contrast-to-noise ratio (CNR). With a proper design, the CNR for an artifact-free overlapping system can be significantly higher than that for the corresponding nonoverlapping system. The improved image quality is also confirmed with noisy reconstructions. [ABSTRACT FROM AUTHOR]

We developed SPECT imaging capability on a LabPET animal scanner to provide an integrated PET/SPECT dual-modality imaging system. The add-on SPECT sub-system was enabled by 1) mechanically integrating a multiple-pinhole collimator in the PET detector ring, and 2) configuring the detectors to acquire singles events in the 120–160 keV range. We report on the design parameters, data acquisition protocols and initial performance assessment of this cost-effective SPECT imaging solution. Phantom and animal images demonstrating the relevance of the system for various imaging tasks in preclinical research are presented. [ABSTRACT FROM PUBLISHER]

Virtual-pinhole PET (VP-PET) imaging is a new technology in which one or more high-resolution detector modules are integrated into a conventional PET scanner with lower resolution detectors. It can locally enhance the spatial resolution and contrast recovery near the add-on detectors, and depending on the configuration, may also increase the sensitivity of the system. This novel scanner geometry makes the reconstruction problem more challenging compared to the reconstruction of data from a stand-alone PET scanner, as new techniques are needed to model and account for the non-standard acquisition. In this paper, we present a general framework for fully 3D modeling of an arbitrary VP-PET insert system. The model components are incorporated into a statistical reconstruction algorithm to estimate an image from the multi-resolution data. For validation, we apply the proposed model and reconstruction approach to one of our custom-built VP-PET systems--a half-ring insert device integrated into a clinical PET/CT scanner. Details regarding the most important implementation issues are provided. We show that the proposed data model is consistent with the measured data, and that our approach can lead to reconstructions with improved spatial resolution and lesion detectability. [ABSTRACT FROM AUTHOR]

SPECT is primarily used in the clinic for cardiac myocardial perfusion imaging. However, for SPECT, sensitivity is impaired due to the need for collimation. System resolution FWHM is poor as well (\sim 1~cm). In this work the resolution of a curved detector was theoretically derived. The advantage of a curved detector over a flat detector with pinhole collimation was demonstrated for cardiac applications using theoretical derivations as well as a ray-tracing voxel-based forward projector. For the flat detector using parameters close to what was expected for the new multi-pinhole GE Discovery system, it is shown that using a paraboloid detector one may obtain a better system resolution (about 29% better on the average), keeping same pinhole opening. Alternately, sensitivity gains of as much as 2.25 may be obtained, for similar resolutions as a flat detector by just using a different pinhole with higher hole-diameter. [ABSTRACT FROM AUTHOR]

In this paper a new method for non-contact scanning of engineering surfaces will be presented. Similar to the classical confocal microscope principal but without using real physical pinholes a new method that uses Digital Micromirror Device (DMD™) as virtual illumination pinhole and selective CCD camera as virtual detection is developed. With this study, this new, flexible and highly accurate a micromirror- based system will be introduced. The concept concerning system layout and system performance together with the measurement results will be presented. Confocal microscopy was first described by M. Minsky in 1957 and in last couple decades it becomes one of the most powerful tool for 3D characterization of complex engineering surfaces. In reflection mode confocal microscopy applications a point illumination source is imaged onto object by using a microscope objective (first focus point). This focusing point on object results with maximum intensity on a detector by passing through the detector pinhole (second focus point) where the lights from defocused neighborhoods object regions are strongly suppressed by the pinhole. In other words, the detector signal that is determined by the pinhole size is reduced strongly by defocusing the specimen. This characteristic of confocal system gives us a chance to make optical sectioning with high vertical resolution discrimination by suppressing the scattered light from defocused object position. It is also well known that confocal microscopy gives some improvements in the sense of lateral resolution compared to the classical microscopy. (DMD™) technology was developed by Texas Instruments. The DMD that used in the setup consists of 600×800 programmable micromirrors. Each of these mirrors has 16μm × 16μm square size with a 1μm gap between them and each mirror tilt ±10° around the diagonal axis with help of underlying memory cel. DMD as a member of MEMS device can also be used as a light switch. … [ABSTRACT FROM AUTHOR]

This paper presents a feasibility study of a Compton scattering enhanced (CSE) multiple pinhole imaging system for gamma rays with energy of 140 keV or higher. This system consists of a multiple-pinhole collimator, a position sensitive scintillation detector as used in standard Gamma camera, and a Silicon pad detector array, inserted between the collimator and the scintillation detector. The problem of multiplexing, normally associated with multiple pinhole system, is reduced by using the extra information from the detected Compton scattering events. In order to compensate for the sensitivity loss, due to the low probability of detecting Compton scattered events, the proposed detector is designed to collect both Compton scattering and non-Compton events. It has been shown that with properly selected pinhole spacing, the proposed detector design leads to an improved image quality. [ABSTRACT FROM AUTHOR]

Pinhole collimators are well suited for small animal SPECT, in which high spatial resolution is required over a small field of view (FOV). Typical pinhole collimators have pinhole angles of 90° or more. If their full FOV is used, the trajectories of imaged gamma-rays can be up to 45° away from the pinhole axis, and form angles of incidence at the surface of a planar detector as large as 45°. The large incident angle produces a depth-of-interaction (DOI) blur thus reducing spatial resolution for these off-axis locations. This loss of the detector resolution is masked by the accompanying improvement of the pinhole point spread function (PSF) due to the reduced effective aperture size. The magnitude of these effects as a function of the angle between the gamma-ray trajectory and the pinhole axis depends on detector absorption efficiency, and on the physical parameters of the pinhole collimator, including pinhole type, composition, and pinhole angle. In addition, the reduced effective pinhole size results in reduced efficiency for off-axis source points. In this paper we investigate the angular dependence of these effects for pinhole collimators with different compositions and pinhole angles. Results are compared to theoretical expressions that take into account gamma-ray penetration of the pinhole material. [ABSTRACT FROM AUTHOR]

For an aperture with transverse size D, Fraunhofer region is named when the distance between the aperture and the detector is larger than D2/λ, where λ is the wavelength of the illuminating light. For a lensless system, when both reference detector and the object are located in Fraunhofer region relative to the thermal source, we demonstrate that a ghost “pinhole” camera with magnification M=z/z1 can be obtained by the second-order correlation of two light fields even if the test detector is a single pointlike detector. Effects determining the quality of ghost pinhole imaging and its potential applications are also discussed. [ABSTRACT FROM AUTHOR]