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Abstract: Transmission sources used for image attenuation correction, allowing image quantification, are collimated to reduce scatter. We propose the same effect can be achieved for an uncollimated source by increasing source to patient distance. The aim was to compare planar image performance characteristics and absorbed doses of uncollimated and collimated radioactive printed paper transmission sources. The scatter contribution to the uncollimated 99mTc source data was evaluated for different combinations of detector phantom distance, detector source distance and phantom source distance. Measurements were performed by increasing the Lucite phantom thickness in 1cm steps to 20 cm. Spatial resolution, detection efficiency and entrance absorbed dose rate were measured for the uncollimated and collimated transmission source images. Results derived from the energy spectra, obtained with the uncollimated transmission source indicate that scatter contribution increases with decreasing detector source distance. The scatter component in the uncollimated transmission images (detector source distances≥60cm; phantom source distances≥40cm) was comparable to that obtained with collimated transmission images. Attenuation coefficients obtained compared well (0.168cm−1 vs. 0.171cm−1). The full widths at half maxima differed by less than 0.9mm. The detection efficiency of the uncollimated source was 2.5 times higher than obtained with the collimated source. The entrance absorbed dose obtained from an uncollimated source was 3.75 times larger than that obtained from the collimated source. An uncollimated transmission source (detector source distance≥60cm) results in acceptable image characteristics and presents a low cost, low dose, high efficiency option for transmission imaging. [ABSTRACT FROM AUTHOR]

Printing‐based organic photodiodes have demonstrated cost effective process and compatibility with Flat Panel industry equipment making large area optical fingerprint sensors viable for volume production. Large area thin film‐based optical collimator enables simple behind display integration. Advantages of this technology are high security level for fingerprint, enhanced ease of use and slim module. [ABSTRACT FROM AUTHOR]

Over the past 100 years, both diagnostic radiology and radiation therapy have grown from infancy to maturity. Accompanying this growth, the discipline of medical physics has evolved and advanced accordingly. New diagnostic and therapeutic procedures continue to be developed, for example, multidetector computed tomography, multileaf collimation, magnetic resonance imaging, dual-source computed tomography, and intensity-modulated radiation therapy. These are now incorporated in health care facilities throughout the world. Modern technologies such as these provide information on underlying pathology at increasingly higher resolutions, generating more information; thus requiring complex methods of image recording and storage. The management of the storage and retrieval of accumulated information is a domain of informatics. In this short review, we describe the different roles of medical physicists and the effective contribution of the American Association of Physicists in Medicine in the evolution of informatics. Medical physicists have contributed to the development of informatics in numerous ways, such as designing hospital information systems and infrastructures that better serve radiologists and other physicians. In addition, the positive exploitation of knowledge gathered in medical settings and effective interdisciplinary collaborations between scientists of different backgrounds have increased. These developments provide future medical physicists the opportunity to develop strategic roles in information technology and thus better contribute to health care. [ABSTRACT FROM AUTHOR]

Electron grid therapy is expected to be a valid treatment for bulky superficial tumors. It is difficult, however, to fit irradiation fields to bulky superficial tumor shapes for conventional electron grid therapy with a cerrobend grid collimator. In this study, we investigated whether a grid collimator using tungsten functional paper (TFP), with its radiation shielding ability, could be used for electron grid therapy. Dose distributions were measured using 9 MeV electron grid beams from a cerrobend grid collimator. For the simulation study, the same grid irradiation fields were shaped using a TFP grid collimator (thicknesses of 0.15, 0.3, 0.6, 0.9, and 1.2 cm) by laying them on a phantom. We then determined the dose distributions using Monte Carlo calculations and compared the cerrobend and TFP electron grid beams regarding dose distributions, including the depths of the maximum dose (dmax), 90% dose (d90), and 80% dose (d80), and the ratios of the doses in the areas with and without shielding (valley to peak ratios). The equivalent dosimetric thickness was obtained with the TFP grid collimator that was equivalent to the dose distribution of the cerrobend grid collimator. For the cerrobend electron grid beams, the dmax, d90, and d80 were 1.0, 2.1, and 2.5 cm, respectively, and the valley to peak ratios at those depths were 0.48, 0.66, and 0.73, respectively. The equivalent dosimetric thickness of TFP was 0.52 cm. The dmax, d90, and d80 for the 0.52 cm thick TFP electron grid beams were 1.1, 1.9, and 2.3 cm, respectively, and the valley to peak ratios at those depths were 0.49, 0.63, and 0.71, respectively. The TFP grid collimator flexibly delivered excellent dose distributions by simply attaching it to the patient’s skin. It could thus be used for electron grid therapy instead of the cerrobend grid collimator. [ABSTRACT FROM AUTHOR]

Purpose: This paper describes the implementation of an instantaneous low‐dose‐rate total body irradiation (TBI) technique using block‐filtered 6 MV X‐rays with a linear accelerator (LINAC) to reduce pulmonary toxicity. Methods: In the absence of dedicated TBI‐specific meter‐set dose rates in LINAC and sufficient treatment room size, a 2‐cm‐thick transmission block was used together with a 200‐cm source‐to‐surface distance (SSD) to reduce the instantaneous dose rates of 6 MV x‐rays down to 10 cGy/min, thus alteration to the beam properties. A TBI‐specific dose calculation model was built with data acquired at the treatment planning system (TPS)‐permitted maximum 140‐cm SSD and was validated in phantoms at a 180‐cm SSD. As for planning strategies, we adopted large anterior‐to‐posterior/posterior‐to‐anterior (AP/PA) open fields with multi‐leaf collimator shielding for lungs to achieve target coverage, lung protection, and efficient dose delivery. A custom‐designed sliding couch (Patent No. ZL202123085880.1) was manufactured to support patients during treatment. Measures to control the quality and safety of TBI treatment include machine interlocks, pretreatment checklists, and in‐vivo dose monitoring. Results: The instantaneous dose rate of block‐filtered 6MV X‐ray was reduced to approximately 7.0 cGy/min at 12.5–7.5 cm depth with a 185–200 cm SSD. The dose calculated by TPS differs from the measurements by 0.15%–1.55% in the homogeneous phantom and 1.2%–4.85% in the CIRS thorax phantom. The open‐field TBI technique achieved V90% (PTV) ≈ 96.8% and MLD = 6.6 Gy with 1‐h planning and 50‐min beam delivery in a single fraction. From February 2021 to July 2023, 30 patients received TBI treatments in our center, and in‐vivo monitoring results differed from TPS calculations by −1.49%–2.10%. After 6–12 months of follow‐ups, all the patients treated in our center showed no pulmonary toxicities of grade 2 or higher. Conclusion: A low instantaneous dose rate TBI technique can be implemented in the clinic. [ABSTRACT FROM AUTHOR]

With off-axis reflection systems with specific distortion values serving as objectives or collimators, it is possible to compensate and correct for spectral line bending in spectroscopic instruments. However, there is limited research on the precise control of distortion, which poses particular challenges in large field-of-view optical systems. This paper presents a method for controlling distortion in off-axis reflection systems. Based on Seidel aberration theory and the relationship between distortion wavefront error and primary ray error, we construct objective functions with structural constraints and aberration constraints. The initial structure with specific distortion values is then solved using a differential evolution algorithm. The effectiveness and reliability of this method are verified through the design of an off-axis three-reflection system. The method provided in this study facilitates the design of remote sensing instruments. [ABSTRACT FROM AUTHOR]

A graded-index (GI)-type photonic crystal fiber (PCF) that has an α-power effective refractive index profile operates as a multimode optical fiber and can be applied to a collimator for single-mode PCFs. The α-power effective index distribution is realized by an α-power air hole diameter distribution with uniform air hole pitch. However, a pressure controlling in fiber drawing is difficult due to the difference of air hole diameters in fiber cross section. In this paper, we propose a GI-PCF with uniform air hole diameter while the air hole pitch varies in radial direction. Light propagation characteristics in the Gaussian beam excited GI-PCF with uniform air hole diameter were theoretically studied. The period and amplitude of mode field diameter variation along the propagation direction for the innermost air hole pitch, air hole diameter, and radial distribution profile of the pitch were clarified. The collimator application of GI-PCF with uniform air hole diameter for a conventional single-mode PCF was investigated. The suitable GI-PCF structure to obtain high optical coupling efficiency and good tolerance for GI-PCF length error was clarified. Wavelength characteristics of the GI-PCF collimator were also studied. It was clarified that the appropriate GI-PCF length was longer for shorter operating wavelength in collimator application. [ABSTRACT FROM AUTHOR]

Objective. Spatially fractionated radiotherapy is showing promise as a treatment modality. Initial focus was on beams of photons at low energy produced from a synchrotron but more recently research has expanded to include applications in proton therapy. Interest in photon beams remains and this is the focus of this paper Approach. This study presents a 3D printed tungsten minibeam collimator intended to produce peak-to-valley dose ratios (PVDR) of between seven and ten with a 1 MV, bremsstrahlung generated, photon beam. The design of the collimator is motivated by a Monte Carlo study estimating the PVDR for different collimator designs at different energies. This collimator was characterised on a clinical linear accelerator (Elekta VersaHD) as well as an orthovoltage unit. Main results. The performance of the fabricated collimator was measured on Elekta VersaHD running in unflattened mode with a 6 MV beam. On the Elekta VersaHD units the PVDR was measured to be between approximately 1.5 and 2.0 at 3 cm deep. For measurements with the orthovoltage unit PVDRs of greater than 10 were observed at a depth of 4 cm. Significance. The results confirmed that the predictions from simulation could be reproduced on linear accelerators currently in clinical usage, producing PVDRs between 2–2.5. Using the model to predict PVDRs using 1 MV photon beams, the threshold considered to produce enhanced normal tissue dose tolerance ( > 7) was surpassed. This suggests the possibility of using such techniques with versions of existing Linac technology which have been modified to operate at low energy and high beam currents. [ABSTRACT FROM AUTHOR]

In this paper, we used the single-photon emission computerized tomography (SPECT) imaging technique to visualize the deficiency of dopamine-generated patterns inside the brain. These patterns are used to establish a patient's disease progression, which helps distinguish the patients into different categories. Furthermore, we used a convolutional neural network (CNN) model to classify the patients based on the dopamine level inside the brain. The dataset used throughout this paper is the Parkinson's progressive markers initiative (PPMI) dataset. The collected dataset was pre-processed and data amplification was performed to balance the imbalanced dataset. A CNN-based neural network was defined to classify input SPECT images into four categories. The motivation behind the proposed model is to reduce the number of resources consumed while maintaining the performance of the classification model. This will help the healthcare ecosystem run the classification model on mobile devices. The proposed model contains 14 layers with input layers, convolutional layers, max-pool layers, flatten layers, and dense layers with different dimensions. The dense layer classifies the patients into four different categories, including PSD, healthy control, scans without evidence of dopaminergic deficit (SWEDD), and GenReg PSD from the entire SPECT imaging dataset, which is used to establish the disease progression of different patients using SPECT images. The proposed model is trained with a large dataset with 58,692 images for training and 11,738 images for validation, and 7826 for testing. The proposed model outperforms the classification models from the surveyed papers. The proposed model's accuracy is 0.889, recall is 0.9012, the precision is 0.9104, and the F1-score is 0.9057. [ABSTRACT FROM AUTHOR]

In traditional cesium beam clocks, cesium atoms are deflected by strong inhomogeneous magnetic fields. The distribution of the detectable atoms, which is critical to the short-term frequency stability, is hard to describe with analytical functions. In this paper, we numerically analyze the beam optics performance of cesium beam tubes based on the magnetic-state-selected and fluorescence detection scheme. To accurately model the cesium beam tube, we apply the Monte Carlo sampling directly inside the collimator. The finite element method is also applied to model the magnetic field. Upon the high dimensional distribution space, two key parameters are selected as indicators of the short-term performance of the cesium beam tube, the effective velocity distribution, and the normalized density difference of atoms in | F = 3 , m F = 0 ⟩ and | F = 4 , m F = 0 ⟩. The influence of the configuration of the collimator is analyzed. Experiments are carried out with two manufactured beam tubes. The results show good agreement with the simulation model. We also discuss limitations of the simulation method when applied to designing cesium beam tubes. [ABSTRACT FROM AUTHOR]

X-ray fluorescence computed tomography (XFCT) has attracted wide attention due to its ability to simultaneously and nondestructively obtain structural and elemental distribution information within samples. In this paper, we presented an image system based on the pinhole collimator for the polychromatic L-shell XFCT to reduce time consumption and improve the detection limit. First, the imaging system model was expressed by formulas and discretized. Then, two phantoms (A and B) were scanned by numerical simulation and Monte Carlo simulation. Both phantoms with the same diameter (10 mm) and height (10 mm) were cylinders filled with PMMA, and embedded with GNP-loaded cylinders. The phantom A was inserted by six 1.5 mm-diameter cylinders with different Au concentrations ranging from 0.2% to 1.2%. The phantom B was inserted by eight cylinders with the same Au concentration (1%), but a radius ranging from 0.1 mm to 0.8 mm. Finally, the reconstruction of the XFCT images was performed using the method with and without absorption correction, respectively. The feasibility of XFCT system presented in this paper was demonstrated by the numerical simulation and the Monte Carlo simulation. The results show that absorption attenuation can be corrected by the presented method, and the contrast to noise ratio (CNR) is proportional to Au concentration but almost remains unchanged with the radius of GNP-loaded cylinders, which may provide the necessary justification for further optimization of the imaging system. [ABSTRACT FROM AUTHOR]

The safe operation of the European Organization for Nuclear Research Large Hadron Collider relies on a complex system for equipment protection. An essential part of machine protection is the collimation system since it is used to protect the equipment from beam losses. This is achieved by using two jaws to intercept the particles making up the beam halo. Since the jaws are in close proximity to the beam, they must be positioned with micrometer precision from it. An ironless inductive position sensor (I2PS) is a relatively new linear position sensor used to measure the distance of the jaws with respect to the beam. During the operation, it is noted that the position read by the I2PS could be affected by temperature variation causing position-reading errors. This paper presents an experimental study conducted on the I2PS to determine the relationship between the position read by this transducer and the ambient temperature. Furthermore, this paper aims at determining the impact of the temperature changes in the collimator body, on which the I2PS is installed, and the position read by the sensor. The results show that the uneven thermal distribution along the body of the sensor leads to high position readings error. These results also show that, depending on the moving coil position, the sensor behaves differently, and hence, it is very difficult to compensate for the effect. Finally, this paper presents the results of a possible modification tested on the same setup to reduce the thermal effects. [ABSTRACT FROM AUTHOR]

Abstract. A newly designed technique for experimental single-photon emission tomography (SPET) and positron emission tomography (PET) data acquisition with minor disturbing effects from scatter and attenuation has been developed. In principle, the method is based on discrete sampling of the radioactivity distribution in 3D objects by means of equidistant 2D planes. The starting point is a set of digitised 2D sections representing the radioactivity distribution of the 3D object. Having a radioactivity-related grey scale, the 2D images are printed on paper sheets using radioactive ink. The radioactive sheets can be shaped to the outline of the object and stacked into a 3D structure with air or some arbitrary dense material in between. For this work, equidistantly spaced transverse images of a uniform cylindrical phantom and of the digitised Hoffman rCBF phantom were selected and printed out on paper sheets. The uniform radioactivity sheets were imaged on the surface of a low-energy ultra-high-resolution collimator (4 mm full-width at half-maximum) of a three-headed SPET camera. The reproducibility was 0.7% and the uniformity was 1.2%. Each rCBF sheet, containing between 8.3 and 80 MBq of [sup 99m] TcO[sub 4]-depending on size, was first imaged on the collimator and then stacked into a 3D structure with constant 12 mm air spacing between the slices. SPET was performed with the sheets perpendicular to the central axis of the camera. The total weight of the stacked rCBF... [ABSTRACT FROM AUTHOR]

As part of its research and development activities on high-energy X-ray imaging for nondestructive characterization, the Nuclear Measurement Laboratory has started an upgrade of its imaging system currently implemented at the CEA-Cadarache Center. The goals are to achieve a submillimeter spatial resolution and the ability to perform tomographies on very large objects (more than 100-cm standard concrete or 40-cm steel). This paper presents the results on the detection part of the imaging system. The upgrade of the detection part needs a thorough study of the performance of two detectors: a series of CdTe semiconductor sensors and two arrays of segmented CdWO4 scintillators with different pixel sizes. This paper consists of a quantum accounting diagram analysis coupled with Monte Carlo simulations. The scintillator arrays should be able to detect the millimeter details through 140 cm of concrete but are limited to 120 cm for the smaller ones. CdTe sensors have lower but more homogeneous performance, with a 0.5-mm resolution for 90 cm of concrete. The choice of the detector then depends on the preferred characteristic: the spatial resolution or the use on large volumes. The combination of the features of the source and the studies on the detectors gives the expected performance of the whole equipment, in terms of signal-over-noise ratio, spatial resolution, and acquisition time. Finally, experimental validations are carried out and validate the simulated performances. [ABSTRACT FROM AUTHOR]

Background: This paper makes use of Monte Carlo (MC) simulation to verify the dosimetric accuracy lung SBRT treatment plans delivered with an Elekta beam modulator multileaf collimator (MLC) system. Materials and Methods: Treatment plans of twenty early stage non-small cell lung carcinoma (NSCLC) patients were retrospectively re-calculated using the collapsed cone convolution (CCC) algorithm of the Pinnacle treatment planning system (TPS). Dose distributions were also calculated using the BEAMnrc and DOSXYZnrc MC user codes. A comparative analysis of target volume and organ at risk (OAR) dosimetry was performed between the TPS and MC dose calculation. A statistical analysis of the two dose distributions and parameters generated by the TPS and MC was performed to examine the significance of any differences. Results: The results showed that the TPS matched within 6% of the MC calculations for the planning treatment volume (PTV) coverage, mean and maximum PTV doses, and conformity index. The differences over all plans for the PTV were not statistically significant. For the organ at risk, the TPS overestimated the mean dose parameters over all patients but was only statistically significant for some organ at risks including the mean lung dose (MLD), V20Gy to the lung and V30Gy to the chest wall. Conclusion: The TPS dose calculation of lung SBRT using CCC Pinnacle³ algorithms is relatively closer to the MC calculation, however there may be inaccuracies in the TPS dose calculation for some patients, manifesting in some of the key dosimetric parameters that are used as correlates for irradiation related complications. [ABSTRACT FROM AUTHOR]

The myocardial single photon emission computed tomography (SPECT) is a good study due to its clinical significance in the diagnosis of myocardial disease and the requirement for improving image quality. However, SPECT imaging faces challenges related to low spatial resolution and significant statistical noise, which concerns patient radiation safety. In this paper, a novel reconstruction system combining multi-detector elliptical SPECT (ME-SPECT) and computer tomography (CT) is proposed to enhance spatial resolution and sensitivity. The hybrid imaging system utilizes a slit-slat collimator and elliptical orbit to improve sensitivity and signal-to-noise ratio (SNR), obtains accurate attenuation mapping matrices, and requires prior information from integrated CT. Collimator parameters are corrected based on CT reconstruction results. The SPECT imaging system employs an iterative reconstruction algorithm that utilizes prior knowledge. An iterative reconstruction algorithm based on prior knowledge is applied to the SPECT imaging system, and a method for prioritizing the reconstruction of regions of interest (ROI) is introduced to deal with severely truncated data from ME-SPECT. Simulation results show that the proposed method can significantly improve the system's spatial resolution, SNR, and image fidelity. The proposed method can effectively suppress distortion and artifacts with the higher spatial resolution ordered subsets expectation maximization (OSEM); slit-slat collimation. [ABSTRACT FROM AUTHOR]

Background and Purpose: Despite the acknowledged need for a stable reference point for LINAC isocenter quality assurance (QA), no standard for such a reference point has been established. This paper introduces a practical and robust technique for measuring and tuning LINAC isocenter within a stable reference frame based on the collimator axes of rotation. Methods: We develop a framework based on physical isocenter, a refinement of the approach by Skworcow et al. The physical isocenter provides a relatively stable, first principles spatial point from which other LINAC parameters can be referenced. An optical tracking system was used to measure the collimator axes with high precision and an isocenter cost function was implemented to ensure a unique isocenter location. The same optical tracking system was used to (a) align the couch axis to the physical isocenter, (b) align the radiation beam to the collimator axes, and (c) position a marker precisely at the physical isocenter to demonstrate the effectiveness of the approach. Results: The framework was successfully demonstrated on an Elekta LINAC. The physical isocenter was shown to be repeatable with a standard deviation of 0.03 mm for the position and 0.03 mm for the radius. The couch axis was aligned to physical isocenter within 0.07 mm. The average collimator to beam axis distance before beam alignment was 0.19 and 0.10 mm after. All these steps were performed within 3 h, showing that the method is efficient when applied to isocenter optimization. The time required to measure physical isocenter and guide a marker to it for day‐to‐day isocenter QA was under 10 min. Conclusions: We have presented a modular, practical framework for isocenter characterization and optimization based on physical isocenter, which is a stable and fixed reference point. [ABSTRACT FROM AUTHOR]

In this paper we describe the Kottamia Faint Imaging Spectro-Polarimeter (KFISP) that has been recently developed and designed to be mounted at the Cassegrain focus of the 1.88 m telescope at Kottamia Astronomical Observatory (KAO), Egypt. The optical design of KFISP is developed such that it can be used in various modes of operation. These are: direct imaging, spectroscopic, polarimetric imaging, and spectro-polarimetric. The KFISP is an all-refractive design to meet the polarimetric requirements and includes a focal reducer with a corrector section, collimator section, parallel beam section (containing various imaging components), and camera section. The corrector section gives an unvignetted Field-of-View of 8ʹ × 8ʹ and the collimator section has a focal length of 305 mm and matches the focal ratio of the input beam. The parallel beam section is 200 mm long and near the middle of it there is an image of the telescope pupil. The camera section includes 5 elements and has a focal length of 154.51 mm which gives an instrument effective final focal ratio of f/6.14 (acting as a telescope focal reducer of 1:2 ratio). The KFISP contains an internal calibration system which hosts the calibration light injection system, an integrating sphere equipped with the required calibration light sources. The opto-mechanical parts of KFISP contain a double-layered carbon fiber strut structure and comprises its subsystems of slit and guider assemblies, filter wheel drawer, grism wheel drawer, polarimetric components cubical box, and CCD camera which is integrated with camera optics. The CCD camera has 2048 × 2048 pixels with 13.5-micron square pixel size. The camera is cooled by liquid Nitrogen and is fixed to the KFISP through the integrated camera lens. The KFISP has been fully commissioned, mounted and is being tested in all modes of operation. In this paper we introduce the ambitious scientific goals, the optical setups of KFISP, its opto-mechanical implementation and the performance analysis of the instrument. In addition, we describe the camera system, its performance, and its software control. Finally, we present a sample of the first light observations obtained from the instrument. [ABSTRACT FROM AUTHOR]

Background: Single photon emission computed tomography (SPECT) is an imaging modality that has demonstrated its utility in a number of clinical indications. Despite this progress, a high sensitivity, high spatial resolution, multi‐tracer SPECT with a large field of view suitable for whole‐body imaging of a broad range of radiotracers for theranostics is not available. Purpose: With the goal of filling this technological gap, we have designed a cadmium zinc telluride (CZT) full‐ring SPECT scanner instrumented with a broad‐energy tungsten collimator. The final purpose is to provide a multi‐tracer solution for brain and whole‐body imaging. Our static SPECT does not rely on the dual‐ and the triple‐head rotational SPECT standard paradigm, enabling a larger effective area in each scan to increase the sensitivity. We provide a demonstration of the performance of our design using a realistic model of our detector with simulated body‐sized phantoms filled with 99mTc and 177Lu. Methods: We create a realistic model of our detector by using a combination of a Geant4 Application for Tomographic Emission (GATE) Monte Carlo simulation and a finite element model for the CZT response, accounting for low‐energy tail effects in CZT that affects the sensitivity and the scatter correction. We implement a modified dual‐energy‐window scatter correction adapted for CZT. Other corrections for attenuation, detector and collimator response, and detector gaps and edges are also included. The images are reconstructed using the maximum‐likelihood expectation‐maximization. Detector and reconstruction performance are characterized with point sources, Derenzo phantoms, and a body‐sized National Electrical Manufacturers Association (NEMA) Image Quality (IQ) phantom for both 99mTc and 177Lu. Results: Our SPECT design can resolve 7.9 mm rods for 99mTc (140 keV) and 9.5 mm for 177Lu (208 keV) in a hot‐rod Derenzo phantom with a 3‐min exposure and reach an image contrast of 78% for 99mTc and 57% for 177Lu using the NEMA IQ phantom with a 6‐min exposure. Our modified scatter correction shows an improved contrast‐recovery ratio compared to a standard correction. Conclusions: In this paper, we demonstrate the good performance of our design for whole‐body imaging purposes. This adds to our previous demonstration of improved qualitative and quantitative 99mTc imaging of brain perfusion and 123I imaging of dopamine transport with respect to state‐of‐the‐art NaI dual‐head cameras. We show that our design provides similar IQ and contrast to the commercial full‐ring SPECT VERITON for 99mTc. Regarding 177Lu imaging of the 208 keV emissions, our design provides similar contrast to that of other state‐of‐the‐art SPECTs with a significant reduction in exposure. The high sensitivity and extended energy range up to 250 keV makes our SPECT design a promising alternative for clinical imaging and theranostics of emerging radionuclides. [ABSTRACT FROM AUTHOR]

This paper describes a procedure for the estimation of 241Am and 239Pu activity present in the human tissue by measuring the depth of contaminant using a portable Planar High Purity Germanium detector (HPGe). The ratios of photopeak counts of X-rays or gammas obtained with the detector coupled to collimator are calculated for the estimation of depth of the contaminant and the optimum one is determined. Since Minimum Detectable Activities (MDA) for the detector coupled to a collimator are higher than that of bare detector, activity must be estimated using bare detector, after locating the contaminant. Two methods are described for the estimation of plutonium coexisting with 241Am: (i) Abundance and isotopic correction for 239Pu (ii) and 239Pu:241Am ratio. The procedure to estimate 239Pu when plutonium isotopes alone are present is also established. An optimum monitoring period to detect the minimum value of intake for both radionuclides corresponding to chelation therapy and excision is also derived. [ABSTRACT FROM AUTHOR]

Introduction: Radiotherapy (RT) may increase the dose of heart structure like left anterior descending coronary artery (LAD). The purpose of this paper was to evaluate the impact of various multileaf collimators (MLCs) in shielding organ at risks (OARs), especially LAD, of patients with left breast cancer. Materials and Methods: Forty-five patients with left breast cancer were selected. The treatment plans were created applying three techniques for all patients. In the first plan (uncovered LAD), the treatment plan was made without considering LAD as OARs. In the two other plans, two MLCs with different leaf widths (6.8 mm and 5 mm) were used to shield the LAD. For all plans, MLC was shielded as much of OAR as possible without compromising planning target volume (PTV) coverage. Dosimetric parameters of the heart, LAD, and ipsilateral lung were assessed. Results: Compared to other plans, the covered LAD plan 1(CL1) obtained lower lung, cardiac, and LAD doses with the same PTV coverage. On average, the mean heart dose decreased from 6.2 Gy to 5.4 Gy by CL1, and the average mean dose to the LAD was reduced from 36.4 Gy to 33.7 Gy, which was statistically significant. The average lung volume receiving >20 Gy was significantly reduced from 24.6% to 23.4%. Moreover, the results show that covered LAD plan 2(CL2) is less useful for shielding OARs compared to CL1. Conclusion: CL1 plans may reduce OAR dose for patients without compromising the target coverage. Hence, the proper implementation of MLC can decrease the side effects of RT. [ABSTRACT FROM AUTHOR]

In response to the demand for operation in non-laboratory environments, there has been a trend toward the development of compact, transportable ultra-stable lasers. This paper reports on this sort of laser system assembled in a cabinet. The whole optical part utilizes fiber-coupled devices to simplify the integration. In addition, spatial beam collimation and alignment into the high-finesse cavity are realized by a five-axis positioner and a focus-adjustable fiber collimator, which significantly relax the alignment and adjustment. A theoretical analysis is performed on how the collimator adjusts the beam profile and coupling efficiency. The support structure of the system is specially designed as well so that it features robustness and transportation without performance degradation. The observed linewidth is 1.4 Hz within a duration of 1 s. After subtracting the linear drift of 70 mHz/s, the fractional frequency instability is better than 4 × 10−15, for the averaging time ranging from 1 to 100 s, which is close to the thermal noise limit of the high-finesse cavity. [ABSTRACT FROM AUTHOR]

This paper proposes a novel alignment system based on the measurement of optical path using a light beam scanning mode in a transmissometer. The system controls both the probe beam and the receiving field of view while scanning in two vertical directions. The system then calculates the azimuth angle of the transmitter and the receiver to determine the precise alignment of the optical path. Experiments show that this method can determine the alignment angles in less than 10 min with errors smaller than 66 ;rad in the azimuth. This system also features high collimation precision, process automation and simple installation. [ABSTRACT FROM AUTHOR]

Deep learning (DL) has a growing popularity and is a well-established method of artificial intelligence for data processing, especially for images and videos. Its applications in nuclear medicine are broad and include, among others, disease classification, image reconstruction, and image de-noising. Positron emission tomography (PET) and single-photon emission computerized tomography (SPECT) are major image acquisition technologies in nuclear medicine. Though several studies have been conducted to apply DL in many nuclear medicine domains, such as cancer detection and classification, few studies have employed such methods for cardiovascular disease applications. The present paper reviews recent DL approaches focused on cardiac SPECT imaging. Extensive research identified fifty-five related studies, which are discussed. The review distinguishes between major application domains, including cardiovascular disease diagnosis, SPECT attenuation correction, image denoising, full-count image estimation, and image reconstruction. In addition, major findings and dominant techniques employed for the mentioned task are revealed. Current limitations of DL approaches and future research directions are discussed. [ABSTRACT FROM AUTHOR]

Featured Application: Inspired by the principle of closed-loop vector model, this paper proposes a new computational model to realize the high precision calibration of the step gauge based on the commercial CMM platform and laser interference technology. According to this method, only real-time measurements of the attitude and displacement changes in the movement of the step gauge are needed for the accurate length value of the step gauge to be obtained. A step gauge is a commonly used length standard for international comparison, and its calibration accuracy is often used as a sign to measure a country's length Calibration and Measurement Capability (CMC). Based on this, some developed countries and developing countries all over the world have been carrying out the research of precision calibration technology for step gauge. On the basis of summarizing the current situation of step gauge calibration technology in other countries, this paper presents a new computational model of step gauge calibration based on the Synthesis Technology of Multi-Path Laser Interferometers (SMLI) and an auto-collimator, which can synthesize the three laser light paths into the measured centerline of step gauge. It is very important to obtain a good measurement accuracy for the step gauge, conformed to the Abbe principle, no matter where it is installed on the CMM measurement platform. In this paper, the development of the mathematical model, the data collection algorithms, data analysis techniques, and measurement uncertainty budgets are discussed. Finally, the experimental measurement is carried out and the measurement accuracy is verified to be effective. The results show that this method can effectively avoid the influence of Abbe error in length measurement, and significantly enhance the calibration accuracy of the step gauge. [ABSTRACT FROM AUTHOR]

This paper presents a two‐stage deep learning framework, RR‐HCL‐SVM, designed to aid in the assessment of residual thyroid tissues following thyroidectomy, utilizing single‐photon emission computed tomography (SPECT) images. Leveraging the power of deep learning, our model offers a comprehensive solution for the detection and assessment of remaining thyroid tissues. To enhance accuracy, we introduce a unique combination of features, incorporating the Radio Scan Index (RSI) and radiomics features. These features not only improve accuracy but also provide valuable insights into tissue characterization. Moreover, we employ efficient clustering techniques for feature dimension reduction, preserving model performance while reducing computational complexity. Experimental results demonstrate the effectiveness of our approach, achieving an impressive F1 score of 0.97, sensitivity of 0.96, and specificity of 0.98. The RR‐HCL SVM framework holds great promise in the clinical setting for the precise evaluation of residual thyroid tissues post‐thyroidectomy, offering potential benefits for patient care and treatment planning. [ABSTRACT FROM AUTHOR]

The newly built back-streaming white neutron beam line (Back-n) at China spallation Neutron Source (CSNS) makes a breakthrough for China's domestic nuclear data measurement, which is pushing nuclear data measurement in China towards higher precision and wider energy range. The neutron flux of the facility was measured at the first beginning since it is an extremely important characterization for the experiment proposal and data analysis. The neutron fluxes under big collimators in end station 1 (ES#1) and end station 2 (ES#2) had been characterized by a fission chamber. In this paper, the first measurement of the neutron flux of Back-n ES#1 with small collimators is reported. The neutron flux from 0.5 eV to 300 MeV was measured by three detectors: a silicon monitor based on a 6LiF sample for the energy range below 200 keV, a fast multi-layer fission ionization chamber for the range from 10 keV to 300 MeV, and a proton recoil telescope for the high energy region from 10 to 70 MeV. The flux and its uncertainty with 50 bins per decade were finally evaluated by combining the data of the three detectors. The integrated flux in the full energy range at CSNS beam power of 100 kW is 1.642 × 106 n/cm2/s, which is consistent with the FLUKA simulation within a difference of about 4%. [ABSTRACT FROM AUTHOR]

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A novel Compton Scanner setup has been built, commissioned and operated at the Max-Planck-Institute for Physics in Munich to collect pulses from bulk events in high-purity germanium detectors for pulse shape studies. In this fully automated setup, the detector under test is irradiated from the top with 661.660 keV gammas, some of which Compton scatter inside the detector. The interaction points in the detector can be reconstructed when the scattered gammas are detected with a pixelated camera placed at the side of the detector. The wide range of accepted Compton angles results in shorter measurement times in comparison to similar setups where only perpendicularly scattered gammas are selected by slit collimators. In this paper, the construction of the Compton Scanner, its alignment and the procedure to reconstruct interaction points in the germanium detector are described in detail. The creation of a first pulse shape library for an n-type segmented point-contact germanium detector is described. The spatial reconstruction along the beam axis is validated by a comparison to measured surface pulses. A first comparison of Compton Scanner pulses to simulated pulses is presented to demonstrate the power of the Compton Scanner to test simulation inputs and models. [ABSTRACT FROM AUTHOR]

It is difficult for sapphire fiber Fabry-Perot (FP) sensors to generate high quality interference fringes because their highly multimode property. In this paper, we report a sapphire fiber FP strain sensing system with high fringe visibility, realized by the use of a self-made fiber collimator. The collimator is made by a quarter-period graded index optical fiber (GIOF) fused to a single mode fiber (SMF). In the contrast experiment, no effective signal was collected from a sensing system without the fiber collimator. While adding a fiber collimator into the sensing system, high visibility interference fringes were collected. The fringe visibility is 49.37% when the FP cavity length is 341.1 μm, and 20.09% when the cavity length is 1343.3 μm. The effective range of the cavity is over 1000 μm. Strain experiment at room temperature shows the measuring range is 10037 μϵ with relative error of 0.37% while the gauge length is 100 mm. High temperature experiment was also carried out and the result shows that the sensor can work at 1300 °C. This method is expected to be helpful for decreasing the difficulty of fabricating high fringe visibility sapphire fiber FP sensors, and increasing the measuring range. [ABSTRACT FROM AUTHOR]

This paper presents the first determination of the improvement in beam divergence when including the ANET Compact Neutron Collimator on an existing thermal neutron beam, obtained with a measuring campaign at the LENA Mark-II TRIGA reactor in Pavia. This novel collimator consists of a sequence of collimating and absorbing channels organised in a chessboard-like geometry. It has a scalable structure both in length and in the field of view. It is characterized by an elevated collimation power within a limited length. Its scalability and compactness are added values with respect to traditional collimating system. The prototype tested in this article is composed of 4 concatenated stages, each 100 mm long, with a channel width of 2.5 mm, delivering a nominal L/D factor of 160. This measuring campaign illustrates the use of the ANET collimator and its potential application in ne [ABSTRACT FROM AUTHOR]

Gamma rays have been extensively investigated for breast imaging using collimators; however, the coded-aperture technique needs to be investigated more. In this paper, we propose an experimental study and Geant4 simulations of MURA mask breast imaging. First, we compare the experimental data against the simulation results carried out using Geant4 (version 10.4) and accreditation phantom. Second, we virtually extend our work by changing the tumor-to-background (TBR) and lesion location parameters. We used 99 m T c as a radioactive source. Good agreement has been seen for the benchmark stage, especially in terms of tumor localization. Moreover, the calculated full width at half maximum (FWHM) and contrast for decoded images (having average values of 8 and 3.5 for TBR between 2 and 10) permitted us to conclude that we can accurately localize small lesions up to lower TBR values by following the decoding procedure of deducing the image of a "blank phantom" (phantom with TBR = 1) every time within a matlab-based program. Hence, this work can be considered a continuously added value to previous investigations for scintimammography imaging. [ABSTRACT FROM AUTHOR]

In Single-Photon Emission Computed Tomography (SPECT), the reconstructed image has insufficient contrast, poor resolution and inaccurate volume of the tumor size due to physical degradation factors. Generally, nonstationary filtering of the projection or the slice is one of the strategies for correcting the resolution and therefore improving the quality of the reconstructed SPECT images. This paper presents a new 3D algorithm that enhances the quality of reconstructed thoracic SPECT images and reduces the noise level with the best degree of accuracy. The suggested algorithm is composed of three steps. The first one consists of denoising the acquired projections using the benefits of the complementary properties of both the Curvelet transform and the Wavelet transforms to provide the best noise reduction. The second step is a simultaneous reconstruction of the axial slices using the 3D Ordered Subset Expectation Maximization (OSEM) algorithm. The last step is post-processing of the reconstructed axial slices using one of the newest anisotropic diffusion models named Partial Differential Equation (PDE). The method is tested on two digital phantoms and clinical bone SPECT images. A comparative study with four algorithms reviewed on state of the art proves the significance of the proposed method. In simulated data, experimental results show that the plot profile of the proposed model keeps close to the original one compared to the other algorithms. Furthermore, it presents a notable gain in terms of contrast to noise ratio (CNR) and execution time. The proposed model shows better results in the computation of contrast metric with a value of 0.68 ± 7.2 and the highest signal to noise ratio (SNR) with a value of 78.56 ± 6.4 in real data. The experimental results prove that the proposed algorithm is more accurate and robust in reconstructing SPECT images than the other algorithms. It could be considered a valuable candidate to correct the resolution of bone in the SPECT images. [ABSTRACT FROM AUTHOR]

When examining patients by single-photon-emission computed tomography, the distribution of a radiopharmaceutical in biological tissues is assessed. An active, fast-growing tumor has an increased uptake of the drug compared to healthy tissues. In recent years, a quantitative assessment of the level of intensity of accumulation of a radiopharmaceutical in tumor lesions has attracted significant interest, since it can be useful for monitoring the effectiveness of prescribed therapy. To obtain quantitative results, it is necessary that the applied reconstruction algorithms include the main factors that influence the formation of the initial data. One of these factors is the geometric resolution of the collimator. It was expected that taking this factor into account would improve the quantitative assessment of tumor lesions in reconstructed images. However, there were "pitfalls" on the way to obtaining quantitative estimates of the accumulation of radiopharmaceuticals. So-called edge artifacts were observed on diagnostic images obtained with allowance for the geometric resolution of the collimator, which manifested themselves as a sharp increase in the intensity of radiopharmaceutical accumulation in small tumors and as oscillations in the intensity of radiopharmaceutical accumulation at the edges in large tumors. The problem of marginal artifacts casts doubt on the correctness of the quantitative assessment of the level of intensity of drug accumulation in tumor lesions. In this paper, we study the problem of edge artifacts using the method of mathematical modeling. In numerical experiments, for the first time, the dependence of the quantitative estimate of the intensity of RPs accumulation on the parameters of the reconstruction algorithm was studied. [ABSTRACT FROM AUTHOR]

This paper summarizes our results and findings made throughout the past years on the way towards a one millimeter thin, flexible, and scalable foil camera. The sensor part of the camera consists of multiple thin-film luminescent concentrator (LC) layers, each of which is sensitive to a different band of the light spectrum. A special optical micro-structure cut into the edges of the LC layers multiplexes the transported light signal into a variant of the Radon transform of the image focused on the LC surface. For increasing the camera's depth of field beyond the sensor surface, various thin-film imaging layers, such as optical Söller collimators realized by means of X-ray lithography on a PMMA wafer, have been investigated. The flexibility and scalability of our thin-film camera has the potential to lead to new human–computer interfaces that are unconstrained in shape and sensing-distance. Applications such as contact-less sensing, smart skin sensors for autonomous robots and industrial machines, and environment sensing for vehicles are imaginable. [ABSTRACT FROM AUTHOR]

According to EAST's experimental plan, the long-pulse and high-power operation of neutral beam injector is the requirement for EAST. In this paper, the operation range of beam perveance is adjusted from 1.9–2.5 μP to 2.5–3.3 μP through changing the voltage ratio of gradient grid/plasma grid from 0.84 to 0.78. The thermal analysis of beamline heat load components shows that with the decrease in the voltage ratio of gradient grid/plasma grid from 0.84 to 0.78, the maximum neutral beam power deposition on the calorimeter increases from 825 to 950 kW when accelerating voltage is 50 kV. The results show that the minimum beam divergence increases from 1.25° to 1.32° and the maximum temperature rise of bending magnet collimator increases from 10 to 27 °C. The results in this paper are helpful to find a balance between increase in power delivery capability and prolongation of beam extraction duration and lay a basis for achieving plasma heating according to the physical experimental requirement of EAST. [ABSTRACT FROM AUTHOR]

A graded-index type photonic crystal fiber (GI-PCF) has a graded effective index distribution that can be realized by an α-power air hole diameter distribution in radial direction. Since a beam diameter varies periodically along the propagation direction in the GI-PCF with Gaussian beam excitation, an appropriate length of GI-PCF should be spliced to a single-mode PCF for collimator application. It is desired that GI-PCF structures to obtain high optical coupling efficiency and good tolerance for fiber length error are designed. In this paper, we theoretically studied coupling characteristics of GI-PCF collimator for conventional single-mode PCF depending on air hole diameter ratio to pitch, where the GI-PCF had parabolic air hole diameter distribution in radial direction, and had the air hole pitch that was equal to that in the conventional single-mode PCF. It was found that the optical coupling efficiency could be higher for larger air hole diameter ratio to pitch, where the coupling efficiency almost equal to that in conventional GI-type multimode fiber (GI-MMF) collimator could be obtained. On the other hand, it was clarified that GI-PCF collimators were more tolerant for fiber length error compared with GI-MMF collimator and that the GI-PCF with smaller air hole diameter ratio to pitch exhibited a better tolerance in fiber length error. We clarified that the GI-PCF collimator had an ability to obtain better wavelength characteristics with fiber length error compared with the GI-MMF collimator. [ABSTRACT FROM AUTHOR]

JUICE, the Jupiter Icy Moons Explorer, ESA’s next L-class mission to the Jovian system, will carry a radiation hard electron monitor (RADEM). It will be the first mission since Galileo to perform long-term measurements of the Jovian radiation environment. RADEM has challenging low mass and power constraints which required novel detector concepts. In this paper, we present a RADEM directionality detector and describe its capability to measure radiation angular variability. [ABSTRACT FROM AUTHOR]

Purpose: SparseCT, an undersampling scheme for compressed sensing (CS) computed tomography (CT), has been proposed to reduce radiation dose by acquiring undersampled projection data from clinical CT scanners (Koesters et al. in, SparseCT: Interrupted‐Beam Acquisition and Sparse Reconstruction for Radiation Dose Reduction; 2017). SparseCT partially blocks the x‐ray beam with a multislit collimator (MSC) to perform a multidimensional undersampling along the view and detector row dimensions. SparseCT undersamples the projection data within each view and moves the MSC along the z‐direction during gantry rotation to change the undersampling pattern. It enables reconstruction of images from undersampled data using CS algorithms. The purpose of this work is to design the spacing and width of the MSC slits and the MSC motion patterns based on beam separation, undersampling efficiency, and image quality. The development and testing of a SparseCT prototype with the designed MSC will be described in a following paper. Methods: We chose a few initial MSC designs based on the guidance from two metrics: beam separation and undersampling efficiency. Both beam separation and undersampling efficiency were measured from numerically simulated photon distribution with MSC taken into consideration. Beam separation measures the separation between x‐ray beams from consecutive slits, taking into account penumbra effects on both sides of each slit. Undersampling efficiency measures the dose‐weighted similarity between penumbra undersampling and binary undersampling, in other words, the effective contribution of the incident dose to the signal to noise ratio of the projection data. We then compared the initially chosen MSC designs in terms of their reconstruction image quality. SparseCT projections were simulated from fully sampled patient projection data according to the MSC design and motion pattern, reconstructed iteratively using a sparsity‐enforcing penalized weighted least squares cost function with ordered subsets/momentum algorithm, and compared visually and quantitatively. Results: Simulated photon distributions indicate that the size of the penumbra is dominated by the size of the focal spot. Therefore, a wider MSC slit and a smaller focal spot lead to increased beam separation and undersampling efficiency. For fourfold undersampling with a 1.2 mm focal spot, a minimum MSC slit width of three detector rows (projected to the detector surface) is needed for beam separation; for threefold undersampling, a minimum slit width of four detector rows is needed. Simulations of SparseCT projection and reconstruction indicate that the motion pattern of the MSC does not have a visible impact on image quality. An MSC slit width of three or four detector rows yields similar image quality. Conclusion: The MSC is the key component of the SparseCT method. Simulations of MSC designs incorporating x‐ray beam penumbra effects showed that for threefold and fourfold dose reductions, an MSC slit width of four detector rows provided reasonable beam separation, undersampling efficiency, and image quality. [ABSTRACT FROM AUTHOR]

Purpose: Current methods for patient‐specific voxel‐level dosimetry in radionuclide therapy suffer from a trade‐off between accuracy and computational efficiency. Monte Carlo (MC) radiation transport algorithms are considered the gold standard for voxel‐level dosimetry but can be computationally expensive, whereas faster dose voxel kernel (DVK) convolution can be suboptimal in the presence of tissue heterogeneities. Furthermore, the accuracies of both these methods are limited by the spatial resolution of the reconstructed emission image. To overcome these limitations, this paper considers a single deep convolutional neural network (CNN) with residual learning (named DblurDoseNet) that learns to produce dose‐rate maps while compensating for the limited resolution of SPECT images. Methods: We trained our CNN using MC‐generated dose‐rate maps that directly corresponded to the true activity maps in virtual patient phantoms. Residual learning was applied such that our CNN learned only the difference between the true dose‐rate map and DVK dose‐rate map with density scaling. Our CNN consists of a 3D depth feature extractor followed by a 2D U‐Net, where the input was 11 slices (3.3 cm) of a given Lu‐177 SPECT/CT image and density map, and the output was the dose‐rate map corresponding to the center slice. The CNN was trained with nine virtual patient phantoms and tested on five different phantoms plus 42 SPECT/CT scans of patients who underwent Lu‐177 DOTATATE therapy. Results: When testing on virtual patient phantoms, the lesion/organ mean dose‐rate error and the normalized root mean square error (NRMSE) relative to the ground truth of the CNN method was consistently lower than DVK and MC, when applied to SPECT images. Compared to DVK/MC, the average improvement for the CNN in mean dose‐rate error was 55%/53% and 66%/56%; and in NRMSE was 18%/17% and 10%/11% for lesion and kidney regions, respectively. Line profiles and dose–volume histograms demonstrated compensation for SPECT resolution effects in the CNN‐generated dose‐rate maps. The ensemble noise standard deviation, determined from multiple Poisson realizations, was improved by 21%/27% compared to DVK/MC. In patients, potential improvements from CNN dose‐rate maps compared to DVK/MC were illustrated qualitatively, due to the absence of ground truth. The trained residual CNN took about 30 s on a single GPU (Tesla V100) to generate a 512×$\; \times \;$512×$\; \times \;$130 dose‐rate map for a patient. Conclusion: The proposed residual CNN, trained using phantoms generated from patient images, has potential for real‐time patient‐specific dosimetry in clinical treatment planning due to its demonstrated improvement in accuracy, resolution, noise, and speed over the DVK/MC approaches. [ABSTRACT FROM AUTHOR]

In order to give full play the unique advantage of micro-opto-eclectro-mechanical system (MOEMS) sensor, one novel low-cost plate-type MOEMS uniaxial vibration sensor based on metal etching and fiber collimator technique is proposed and studied in this paper. Core vibration element of the MOEMS vibration sensor is fabricated by the metal etching technique, and its fiber collimator instrument is made up by ultra-polished ceramic ferrule and plane fiber flange. All these techniques can reduce the fabrication cost of the MOEMS vibration sensor greatly. A theory calculation model of the MOEMS vibration sensor is established and further verified by simulation experiments. The first-order resonant frequency of the MOEMS vibration sensor obtained from the simulation experiment is 1536 Hz. Lower resonant frequency confirms that the MOEMS vibration senor can achieve high-precision acceleration measurement theoretically. Limited by detection frequency range of the reference sensor, amplitude calibration experiment of fixed frequency (500 Hz) is carried out and experiment results prove the excellent performance of the MOEMS vibration sensor. [ABSTRACT FROM PUBLISHER]

This paper presents the preliminary results on the early cancer detection using wire mesh collimator gamma camera. The limitation of the conventional multihole collimator is the lacked of sensitivity as a trade-off for obtaining better resolution, hence less photon are registered by the sequential event. This inherent property of the conventional system reduced the possibility of maximum tumour recognition. The wire-mesh collimator is a new concept of semi-collimator and semi-coded aperture. With such a flexible structure, one may choose to have a good resolution or a good sensitivity or any configuration in between. In this paper, we investigate the performance of the wire-mesh collimator to detect a lesion. The imaging environment is modeled using Monte Carlo N-Particle Transport Code version 5 (MCNP5). The results imply that the wire mesh collimator has better sensitivity and recorded more counts than the conventional collimator. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the design study for a brain SPECT imaging system, referred to as the HelmetSPECT system, based on a spherical synthetic compound-eye (SCE) gamma camera design. The design utilizes a large number ($\sim 500$) of semiconductor detector modules, each coupled to an aperture with a very narrow opening for high-resolution SPECT imaging applications. In this study, we demonstrate that this novel system design could provide an excellent spatial resolution, a very high sensitivity, and a rich angular sampling without scanning motion over a clinically relevant field-of-view (FOV). These properties make the proposed HelmetSPECT system attractive for dynamic imaging of epileptic patients during seizures. In ictal SPECT, there is typically no prior information on where the seizures would happen, and both the imaging resolution and quantitative accuracy of the dynamic SPECT images would provide critical information for staging the seizures outbreak and refining the plans for subsequent surgical intervention.We report the performance evaluation and comparison among similar system geometries using non-conventional apertures, such as micro-ring and micro-slit, and traditional lofthole apertures. We demonstrate that the combination of ultrahigh-resolution imaging detectors, the SCE gamma camera design, and the micro-ring and micro-slit apertures would offer an interesting approach for the future ultrahigh-resolution clinical SPECT imaging systems without sacrificing system sensitivity and FOV. [ABSTRACT FROM AUTHOR]

The Ironless Inductive Position Sensor (I2PS) has been introduced as a valid alternative to Linear Variable Differential Transformers (LVDTs) when external magnetic fields are present. Potential applications of this linear position sensor can be found in critical systems such as nuclear plants, tokamaks, satellites and particle accelerators. This paper analyzes the performance of the I2PS in the harsh environment of the collimators of the Large Hadron Collider (LHC), where position uncertainties of less than 20 μm are demanded in the presence of nuclear radiation and external magnetic fields. The I2PS has been targeted for installation for LHC Run 2, in order to solve the magnetic interference problem which standard LVDTs are experiencing. The paper describes in detail the chain of systems which belong to the new I2PS measurement task, their impact on the sensor performance and their possible further optimization. The I2PS performance is analyzed evaluating the position uncertainty (on 30 s), the magnetic immunity and the long-term stability (on 7 days). These three indicators are assessed from data acquired during the LHC operation in 2015 and compared with those of LVDTs. [ABSTRACT FROM AUTHOR]