Active Collimator Research Articles

Charge Sharing Assessment and Active Collimation in Monolithic Arrays of Silicon Drift Detectors

Charge Sharing Assessment and Active Collimation in Monolithic Arrays of Silicon Drift Detectors

A novel active collimator for compton-suppressed clover HPGe detector and its role in a hybrid gamma detector array

A new active collimator (AC) detector has been designed as a replacement of the heavy metal collimator for the Compton-suppressed clover High Purity Germanium (HPGe) detector, aiming to enhance the performance of the 4π hybrid gamma detector array for nuclear spectroscopy experiments. This replacement promises enhanced functionality and efficiency in detecting gamma radiation within the detector array. By utilizing ACs in combination with Compton-suppressed clover HPGe and LaBr3(Ce) detectors, a highly effective setup can be established for a γ-ray multiplicity filter for angular momentum selection in heavy ion collision reactions. This configuration offers notable advantages when studying weak band structures that undergo decay through high-cut multiplicity γ-ray events. Moreover, by summing the energy deposited in all detectors, the hybrid array can also be effectively utilized for calorimetric applications in specific measurements. We have designed and characterized an AC with a Compton-suppressed clover HPGe detector. Significantly, when using the AC configuration with the 60Co source, the absorption of γ-rays in AC and the peak-to-total ratio in clover HPGe were found to be similar to that obtained with the standard design incorporating the heavy metal configuration. The advantages of employing the AC for higher multiplicity events were demonstrated through GEANT4 simulations. The simulations were conducted for the entire array, and the potential benefits are thoroughly discussed, highlighting the improved performance achievable with the AC configuration.

A Compact Particle Detector for Space-Based Applications: Development of a Low-Energy Module (LEM) for the NUSES Space Mission

NUSES is a planned space mission aiming to test new observational and technological approaches related to the study of relatively low-energy cosmic rays, gamma rays, and high-energy astrophysical neutrinos. Two scientific payloads will be hosted onboard the NUSES space mission: Terzina and Zirè. Terzina will be an optical telescope readout by SiPM arrays, for the detection and study of Cerenkov light emitted by Extensive Air Showers generated by high-energy cosmic rays and neutrinos in the atmosphere. Zirè will focus on the detection of protons and electrons up to a few hundred MeV and to 0.1–10 MeV photons and will include the Low Energy Module (LEM). The LEM will be a particle spectrometer devoted to the observation of fluxes of relatively low-energy electrons in the 0.1–7-MeV range and protons in the 3–50 MeV range along the Low Earth Orbit (LEO) followed by the hosting platform. The detection of Particle Bursts (PBs) in this Physics channel of interest could give new insight into the understanding of complex phenomena such as eventual correlations between seismic events or volcanic activity with the collective motion of particles in the plasma populating van Allen belts. With its compact sizes and limited acceptance, the LEM will allow the exploration of hostile environments such as the South Atlantic Anomaly (SAA) and the inner Van Allen Belt, in which the anticipated electron fluxes are on the order of 106 to 107 electrons per square centimeter per steradian per second. Concerning the vast literature of space-based particle spectrometers, the innovative aspect of the LEM resides in its compactness, within 10 × 10 × 10 cm3, and in its “active collimation” approach dealing with the problem of multiple scattering at these very relatively low energies. In this work, the geometry of the detector, its detection concept, its operation modes, and the hardware adopted will be presented. Some preliminary results from the Monte Carlo simulation (Geant4) will be shown.

Active Collimator for the BGO Anti-Compton Shield of the HPGe Clover Detector

Active Collimator for the BGO Anti-Compton Shield of the HPGe Clover Detector

COMPARISON OF PEDIATRIC LENS DOSE MEASUREMENTS BETWEEN AXIAL SCAN MODE WITHOUT ACTIVE COLLIMATOR AND HELICAL SCAN MODE WITH ACTIVE COLLIMATOR BY USING A 64 DETECTOR-ROW COMPUTED TOMOGRAPHY SCANNER.

To investigate the pediatric eye lens entrance surface dose for both axial scan modes without an active collimator and helical scan modes with an active collimator on 64 detector-row computed tomography (CT) scanner. We used three pediatric anthropomorphic phantoms with axial and helical scan modes from the superior orbitomeatal line to the crown of the head. We compared the measured dose values of the real-time skin dosemeter at the surfaces of the lens and the image noise at different scan modes. The median measured dose values for the lens of newborn, 1-year-old and the 5-year-old phantom were 31.3, 0.97 and 0.65mGy, respectively, in the axial scan mode and 0.89, 1.21 and 0.71mGy, respectively, in the helical scan mode. Compared with helical scans with an active collimators, axial scans can reduce the lens dose by ∼10% during head CT on 64 detector-row CT scanner without deterioration of image noise.

Contiguous perfect coded aperture patterns with high throughput.

A method is described that mosaics linear uniformly redundant arrays and modified uniformly redundant arrays onto a square lattice to create coded aperture patterns of approximately 50% throughput that are contiguous, whereby every opaque element in the aperture is joined to at least one other opaque element. Parameters required to create these perfect high-throughput contiguous apertures for all coded aperture unit pattern orders of up to 300 elements are presented. The apertures presented increase significantly the number of known contiguous apertures in dimensions forbidden to the known patterns and that have the same imaging quality as uniformly redundant arrays and modified uniformly redundant arrays while having imaging quality superior to other known self-supporting apertures. The effect of supporting the weaker areas of these contiguous apertures is investigated. Contiguous apertures are of interest for coded aperture systems that require extra rigidity or use active collimation.

Integration of the function generation synthesis into the design of a multi-leaf collimator

Throughout recent history, medical robots have gained a lot of popularity in robotic assisted radiotherapy. Integration of robot manipulators into the field of radiotherapy has improved the chances of patient recovery by increasing system precision, operation reliability and treatment efficiency. In order to prevent healthy tissues from radiation exposures during treatments, linear accelerators of radiotherapy robots have been enhanced by the implementation of active collimator designs. Addition of collimator mechanisms to these systems has also increased possibilities of treatments by allowing adjustable beam geometries on the targets. However, as the collimator leaves are additional obstacles on the path of the beam, beam scattering has become one of the most crucial issues waiting to be improved for these systems. In order to propose a solution for this problem, current paper tries to implement function generation synthesis into a multi-leaf active collimator design, where the individual collimator blocks are stacked vertically. This study demonstrates the proposed approach by utilizing two single degree of freedom planar systems positioned side by side for a point beam source. Throughout the study, kinematic synthesis approach was introduced to design these planar systems to adjust beam contour geometries on a single axis. At the end of the study, proposed procedure was verified by a numerical example and the results were used to design four degrees of freedom collimator that is able to adjust beam contour geometries on the plane. The prototype of the system was also modelled in order to ensure the realization of the collimator design for contour adjustments.

The Cygnus A Jet: Parabolic Streamlines up to Kiloparsec Scales

Abstract We investigated the distance dependence of the transverse width of the jet W(r) of Cygnus A, one of the typical Fanaroff–Riley type II radio galaxies; the radial (deprojected) distance r ranged from 0.28 pc to 60 kpc (from 1.1 × 103 to 2.4 × 108 R S) on both the approaching and counter-jet sides. The power-law dependences (W(r) ∝ r a ) of the jet-width profile in the parsec-scale and kiloparsec-scale regions consistently show a ∼ 0.55. For the first time, we have discovered that active collimation, i.e., a smooth reduction in the opening angle with increasing distance, persists up to distances beyond the Bondi radius. We have also discovered an apparent discontinuity in the radial profiles of the jet width, by which the jet downstream appears to widen a factor of six compared with the expectation from extrapolating the upstream profile, at the radial distance between 57 and 170 pc (from 2.3 × 105 to 6.8 × 105 R S, including the Bondi radius for Cygnus A), which is a blank in our measurements. We discuss possible explanations. The cross-section of jets was physically inflated and collimation again owing to the loss of dynamic equilibrium or a recollimation shock in a relatively flat profile of ambient pressure. We also discuss an alternative possibility to explain the observed discontinuity by a multi-layered structure in the jets: an outer (slower) layer and an inner (faster) layer with flows that are progressively accelerated with distance, throughout the parabolic streamline. The outer layer would be in lower brightness at small distances, whereas the inner layer attenuates at large distances, due to Doppler debeaming as a highly inclined jet of Cygnus A.

Dramatic Dose Reduction in Three-Dimensional Rotational Angiography After Implementation of a Simple Dose Reduction Protocol

Previously, median effective dose (ED) of 1.6 mSv per three-dimensional rotational angiography (3DRA) has been reported. This study evaluated ED and image quality in 3DRA after implementation of a simple dose reduction protocol in pediatric catheterizations. Simple conversion factors between 3DRA ED and readily available parameters at the cathlab were determined. The dose reduction protocol consisted of frame reduction (60–30 frames/s (f/s)), active collimation of the X-ray beam, usage of a readily available low dosage program, and a pre-3DRA run check. EDs were calculated with Monte Carlo PCXMC 2.0. Three observers blindly assessed 3DRA image quality of the dose reduction and normal-dose cohort. Between October 2014 and October 2015, 84 patients (median age 4.3 years) underwent 100 3DRAs with a median ED of 0.54 mSv (0.12–2.2) using the dose reduction protocol. Median ED in the normal-dose cohort (17 3DRAs) was 1.6 mSv (1.2–4.9). Image quality in the dose reduction cohort remained excellent. Correlations between ED and dose area product (DAP) and ED and skin dose were found with a ρ of 0.82 and 0.83, respectively. ED exposure of the entire catheterization was reduced to 2.64 mSv. Introduction of a simple protocol led to 66% dose reduction in 3DRA and 79% in the entire catheterization. 3DRA image quality in this group remained excellent. In 3DRA ED correlates well with DAP and skin dose, parameters readily available at the cathlab.

Clinical validation of CT image reconstruction with interior tomography.

Active x-ray collimation is well adopted in radiography and fluoroscopy for radiation dose reduction and image quality improvement. The application of this concept in computed tomography (CT) is significantly limited due to the truncation of projection data. Generally, an internal field of view (FOV) inside an imaging object cannot be exactly reconstructed only from the truncated projection data. Recent research shows that given some prior information of the FOV image, interior tomography can provide a unique and stable solution for image reconstruction of an internal FOV. The objective of this study is to evaluate the performance of interior reconstruction based on patient datasets obtained from a clinical CT scanner with dual x-ray tubes, which simultaneously gives full projections and truncated projections. Image reconstructions are performed from full and truncated projection data for the comparison of image quality, respectively. The reconstructed CT images were reviewed by a radiologist and a resident. The evaluation results of two observers showed that CT images reconstructed with truncated projections met clinically diagnostic requirements and were comparable to clinical images. This study demonstrates that with the development of interior tomography, active x-ray collimation in the imaging plane can be readily employed in CT imaging to further reduce patient radiation and improve image quality.

MOJAVE – XIV. Shapes and opening angles of AGN jets

We present 15 GHz stacked VLBA images of 373 jets associated with active galactic nuclei (AGN) having at least five observing epochs within a 20 yr time interval 1994-2015 from the MOJAVE programme and/or its precursor, the 2 cm VLBA Survey. These data are supplemented by 1.4 GHz single-epoch VLBA observations of 135 MOJAVE AGNs to probe larger scale jet structures. The typical jet geometry is found to be close to conical on scales from hundreds to thousands of parsecs, while a number of galaxies show quasi-parabolic streamlines on smaller scales. A true jet geometry in a considerable fraction of AGNs appears only after stacking epochs over several years. The jets with significant radial accelerated motion undergo more active collimation. We have analysed total intensity jet profiles transverse to the local jet ridgeline and derived both apparent and intrinsic opening angles of the flows, with medians of $21.5\deg$ and $1.3\deg$, respectively. The Fermi LAT-detected gamma-ray AGNs in our sample have, on average, wider apparent and narrower intrinsic opening angle, and smaller viewing angle than non LAT-detected AGNs. We have established a highly significant correlation between the apparent opening angle and gamma-ray luminosity, driven by Doppler beaming and projection effects.

Development of the Two-dimensional Region-setting CT System: Development and Basic Evaluation of the Experimental System Using the Active Collimators

Development of the Two-dimensional Region-setting CT System: Development and Basic Evaluation of the Experimental System Using the Active Collimators

KWS-1 high-resolution small-angle neutron scattering instrument at JCNS: current state

The KWS-1 small-angle neutron scattering (SANS) instrument operated by the Jülich Centre for Neutron Science (JCNS) at the research reactor FRM II of the Heinz Maier-Leibnitz Zentrum in Garching near Munich has been recently upgraded. The KWS-1 instrument was updated, from its active collimation apertures to the detector cabling. Most of the parts of the instrument were installed for the first time, including a broadband polarizer, a large-cross-section radio-frequency spin flipper, a chopper and neutron lenses. A custom-designed hexapod in the sample position allows heavy loads and precise sample positioning in the beam for conventional SANS experiments as well as for grazing-incidence SANS under applied magnetic field. With the foreseenin situpolarization analysis the main scientific topic of the instrument tends towards magnetism. The performance of the polarizer and flipper was checked with a polarized3He cell at the sample position. The results of these checks and a comparison of test measurements on a ferrofluid in a magnetic field with polarized and nonpolarized neutrons are presented.

SU-C-12A-06: A Universal Definition for CT Irradiated Length

Purpose: The length of scan shown or calculated from the console is the distance between the center of the starting and ending images. The irradiated length for such a set of images can vary substantially from this distance, depending on the acquisition mode. We propose that the rise to equilibrium function h(λ) be used to uniquely define an irradiated length independent of the details of the scanning process. This method also seamlessly accommodates recent developments in active collimation. Method: h(λ) is determined along the central axis of a long cylindrical phantom, ideally from integration of the dose spread function. For practical reasons h(λ) may be approximated from helical scans with real-time dose rate measurements or from a series of central dose measurements using finite irradiated length exposures. For a particular scan then, the irradiated length λ is calculated from a central dose measurement of h and then applying the inverse function h(λ)-1. Results: h(λ) was determined from measurements made in a prototype ICRU/TG200 phantom, 60 cm long and 30 cm in diameter. The resultant λ generally agreed with indicated scan length plus one beam width for axial and indicated scan length for helical scans if overscanning was accounted for. For most scanners, DLP/CTDIvol is a good measure of irradiated length allowing for another index of comparison. Conclusion: Central dose measurements with a small chamber along with the rise to equilibrium function h(λ) provide us with a robust and consistent means of determining scan length independent of the means of irradiation over a variety of scanners and scanning conditions. The method is limited to λ significantly less than the equilibrium.

A cubic gamma camera with an active collimator

Mechanical collimation with photon absorption and electronic collimation using Compton scattering are combined to form a cubic gamma camera with an active collimator. The collimator is made active by constructing it with a uniformly redundant array of patterned Bi4Ge3O12 (BGO) scintillators, which not only attenuates incident radiations but also detects scattered radiation, in a gamma-camera consisting of and five planar CsI(Na) scintillators. The entire module forms a cubic structure that generates images on the basis of radiation interactions from every direction. The coverage angle for detecting scattered radiation is 2π with a detection efficiency approximately 17 times higher than previous systems that comprised only one pair of detectors.

Portable Active Collimation Imager Using URA Patterned Scintillator

A portable active collimator using systematically patterned scintillators was constructed and its performance evaluated. In the conventional passive radiation collimation method, single or multiple holes are used to limit radiation reaching a detector while radiation scattered in the collimator is not used. However in active collimation where one replaces the passive collimator with a radiation detector, both the radiation that passes through the holes and radiation scattered in the collimator can be used. The active collimator was composed of uniformly redundant array (URA)-patterned Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> (BGO) scintillators with a CsI(Na) detector planar array positioned behind the collimator. Images using radiation passing through the holes of the URA collimator were reconstructed using the correlation method of conventional coded apertures, while the radiation scattered in the active collimator and detected in the planar detector, was imaged using a Compton imaging technique. Since the active collimation method uses both Compton scattered events and photoelectric absorption events, its detection efficiency and energy range are inherently higher than those of conventional collimation methods. The reconstructed images of the portable active collimation methods for various energy sources were obtained and compared with those of conventional methods.

Experience with volumetric (320 rows) pediatric CT

The introduction of helical computer tomography (CT) and further progress to multi-slice CT enabled new applications. Most recent developments like the 320-row detector facilitate volume CT, which avoids the over-beaming effect of helical scanning.The 320-row multi-slice detector CT (MDCT) is based on a 16cm detector; a special acquisition mode allows reconstructing 640 slices from these 16cm. The shortest tube rotation time is in cardiac mode 0.35s, otherwise 0.4s and 0.5s used. At 0.5s the machine already reaches the maximum numbers of sub-second projections. Scan modes can be volume, helical and single slice mode. For image acquisition all dose savings technologies like variable tube position for scano-view, active collimation, automated exposure control, bolus and ECG tracking are available. Additionally special acquisition and post-processing techniques like head and body perfusion CT are ready for use on the console. For image reconstruction properties like filtered back projection as well as the latest development of iterative algorithms, an appropriate number of kernels and multi-planar reconstruction in all directions from the volume data at every increment are available. Volume CT allows sub second scanning of 16cm z-coverage which, however, makes administration of intravenous contrast medium to “hit or miss” event.The aim of this paper is to present the application of volume CT to body scanning in children. Representative examples of neck, cardiac and skeletal investigations are given.

Evaluation of dual γ-ray imager with active collimator using various types of scintillators

The performance of a specialized dual γ-ray imager using both mechanical and electronic collimation was evaluated by Monte Carlo simulation (MCNP5). The dual imager consisted of an active collimator and a planar detector that were made from scintillators. The active collimator served not only as a coded aperture for mechanical collimation but also as a first detector for electronic collimation. Therefore, a single system contained both mechanical and electronic collimation. Various types of scintillators were tested and compared with each other in terms of their angular resolution, efficiency, and background noise. In general, a BGO active collimator had the best mechanical collimation performance, and an LaCl 3(Ce) active collimator provided the best electronic collimation performance. However, for low radiation energies, the mechanical collimation images made from both scintillators showed the same quality, and, for high radiation energies, electronic collimation images made from both scintillators also show similar quality. Therefore, if mechanical collimation is used to detect low-energy radiation and electronic collimation is applied to reconstruct a high-energy source, either LaCl 3(Ce) or BGO would be appropriate for the active collimator of a dual γ-ray imager. These results broaden the choice of scintillators for the active collimator of the dual γ-ray imager, which makes it possible to consider other factors, such as machinability and cost, in making the imager. As a planar detector, BGO showed better performance than other scintillators since its radiation detection efficiency was highest of all.

Active collimators in experiments with exotic nuclear beams

The active collimator method for experiments with exotic nuclear beams at energies near the Coulomb barrier of nuclear reactions is described. The technique is based on the use of detectors composed of microchannel plates (MCPs) and thin strips of metal foils (Au, Ag, Al) with a thickness of 200–300 μg/cm2 or less, which are oriented along axes X and Y (axis Z is collinear to the beam axis). Exotic nuclei passing through the foils are detected by the MCPs by electron emission from these foils, which provides a means for obtaining spatial information on the particle trajectory and the time mark of an event. The proposed setup is characterized by the smallest (of the available techniques) material budget on the particle path (≤8.0 × 1017 atoms/cm2) in the zone of detected particles, the high efficiency (ɛ ∼ 90% for every MCP), and the time resolution sufficient for performing additional identification of radioactive nuclei using the time-of-flight method.

Multiple Modality $\gamma$-Ray Imager Using LaCl$_{3}$(Ce) Scintillators With Active Collimation Method

Multiple modality γ-ray imaging using mechanical and electronic collimation with different detection methods was proposed and tested by simulation. Although conventional mechanical collimators, which are made from high atomic number and density materials, passively filter the incident radiation, the mechanical collimator reported in this study consisted of LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) scintillators, which actively collimate the radiation and are used as the 1st detector of an electronic collimator to reconstruct a Compton image. A detector box made from six planar LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) scintillators was positioned behind the active collimator. The LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) scintillator arrays used as the active collimator and box detector consisted of voxels, each 2 mm × 2 mm × 5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in size. A combination of active collimators and box detectors can produce multiple modalities for both mechanical and electronic collimation. The information from each modality was combined effectively using the maximum likelihood expectation maximization (MLEM) method. Therefore, a reconstructed image from multiple modalities has inherently higher efficiency than each conventional modality. The reconstructed images were evaluated using the resolution-variance curve as a quantitative method. Although mechanical collimation is effective at low γ-ray energy and electronic collimation shows high performance at high γ-ray energy, multiple modalities are superior to the conventional single modalities for intermediate γ-ray energies (364 keV). The angular resolution and absolute efficiency were calculated for each modality and source energy.