Special Collimator Research Articles

Transverse beam stability with low-impedance collimators in the High-Luminosity Large Hadron Collider: Status and challenges

The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will double its beam intensity for the needs of High Energy Physics frontier. In order to ensure coherent stability until the beams are put in collision, the transverse impedance has to be reduced. As the major portion of the ring impedance is supplied by its collimation system, several low resistivity jaw materials have been proposed to lower the collimator impedance and a special collimator has been built and installed in the machine to study their effect. The results show a significant reduction of the resistive wall tune shift with novel materials, in agreement with the impedance model and the bench impedance and resistivity measurements. The largest improvement is obtained with a 5 {\mu}m Molybdenum coating of a Molybdenum-Graphite jaw. This coating can lower the machine impedance by up to 30% and the stabilizing Landau octupole threshold by up to 120 A. The collimators to be upgraded have been chosen based on the improvement of the octupole threshold, as well as the tolerance to steady state losses and failure scenarios. A half of the overall improvement can be obtained by coating the jaws of a subset of 4 out of 11 collimators identified as the highest contributors to machine impedance. This subset of low-impedance collimators is being installed during the Long Shutdown 2 in 2019-2020.

P016] Performance of 3 CT scanners: Results from a 4 year period

Purpose Present the results of a 4 years period quality control routine test performed on 3 CT scanners (Siemens Somaton Sensation Open (S), Toshiba Aquilion 16 (T) and Ge HiSpeed Lx/i (G)) to assure compliance of the monitored parameters with baseline values and detect system performance malfunctioning. The weekly test, is a 15 minute check acquisition of the CATPHAN 600 phantom sections. Methods Baseline values were established using the average of 10 images in sequential mode 120 kV, 200 mAs(T), 280 mAs(S) and 300 mAs(G), collimation 1 × 5 mm(SG 31 mGy(G); 35 mGy(S). Performance indicators: Noise Index (standard deviation of the HU measured in a central ROI of 28 cm[b] (40% useful radius) Homogeneity index (maximum difference on the average HU measured in 4 periphery ROI’s relative to a central ROI each with 10cm2); Spatial Resolution Index (zoomed visualization of the last perceptible group of a lp/cm pattern using constant WW, WL); Low Contrast Index (CD – diameter * percentage contrast (mm*%) for each target – 3 groups of different sized low contrast targets 10HU, 5HU, 3HU – 2 images averaged; HU index (average HU in 45 mm[b] ROI’s of 8 target materials from −1000 up to 1000 HU. Results Noise index: σ(T) = 5.36 ± 2%; σ(G) = 2.87 ± 3%; σ(T) = 4.01 ± 5%; maximum deviations: 8.6%(T); 3.1%(G); 4.7%(S); outliers(>10%): two (12.3;16.0%(T)); one 21.6%(G); zero(S). Homogeneity index: HU = 9.53 ± 4%(T); HU = 7.1 ± 3%(G); HU = 12.7 ± 3%(S); maximum difference deviations: 14.7%(T); 14.5%(G); 12.6%(S); outliers(>15%): six(16.7;15.7%(T)) one 24.2%(G); zero(S). Spatial Resolution index (lp/cm): 9(T); 7(G); 8(S); CD index (mm*%): Conclusions The customized test proved to be a simplified but incomplete method for system performance consistency evaluation since it was inefficient in the detection of ring artifacts caused by faults in detector system calibration for the head protocol. The addition of a spiral acquisition in the homogenous section, lead to direct visualization and awareness of this type of artifacts but still do not prevent the detection of artifacts in larger FOVs or in special collimation sets depending on the CT scanner design.

Feasibility of a New Moving Collimator for Industrial Backscatter Imaging

ABSTRACTConventional direct radiography may fail to successfully produce images of corrosion in large pipes containing liquid and in tanks because the attenuation can be very high. It also fails when either side of the object is not accessible. These limitations do not exist in backscatter imaging because it is a one-sided imaging technique. However, backscatter imaging can be slow. In this study, the feasibility of a new backscatter imaging system based on a moving collimator that can produce images quickly is studied. Backscattered radiation from a broad-beam industrial X-ray machine is collimated by a special collimator to allow only parallel scattered radiation to pass and reach the image plate. Because part of the backscattered radiation can be stopped by the collimator septa, the collimator is put into motion; this allows a complete image to be revealed. An electro-mechanical system is designed to move the collimator either in steps or continuously. The distance, speed and direction of the movement are controlled by a smart motor using LabVIEW. Images of Polyvinylchloride (PVC) and aluminum objects are shown. Moving collimators can be added to existing radiographic systems to make them useful for both direct and backscatter imaging.

SU‐F‐T‐670: From the OR to the Radiobiology Lab: The Journey of a Small X‐Ray Source

Purpose:Irradiation of small animal tumor models within laboratories is vital to radiobiological experiments. Often the animals are not able to be brought back into the lab after being taken out for irradiation. Cell biology laboratories benefit from irradiation capability available around the clock without regard to patient load in an associated radiotherapy clinic. Commercial systems are available, but bulky and expensive.Methods:An intraoperative kV irradiation system (IntraBeam™) designed to deliver spherical dose distributions to surgical cavities has been repurposed for the irradiation of cell plates and small laboratory animals. An applicator has been altered to allow for simple, open fields. Special collimators are being developed. BEAMnrc Monte Carlo simulations with the “NRC swept BEAM” source model have been performed to characterize the dose distributions, to develop optimal collimators and as basis for dose prescription. Measurements with radiochromic film and with an ionization chamber were performed to characterize the beam and to validate the simulations.Results:Using its highest setting (50 kV and 40 µA) the x‐ray unit is capable of delivering dose rates over 1 Gy/min homogeneously to standard cell plates even without an optimized collimator. Smaller areas (tumors in animals) can be irradiated with significantly higher dose rates (> 20 Gy/min) depending on distance of the source to the tumor. The HVL was found to be 0.21 mm Al which means the shielding requirements for the device are easily achievable in the lab.Conclusion:A mobile irradiation facility is feasible. It will allow easier access to radiation for radiobiology experiments. The modified system is versatile in that for cell plates homogenous irradiations can be achieved through distance from the source, while for high dose rate small field irradiations the source can be brought in close proximity to the target.

The3H–3He Charge Radii Difference

The upcoming E12-14-009 [1] experiment at Jefferson Lab will determine the ratio of the electric form factors for the A=3 mirror nuclei 3 He and 3 H. The measurement will use a 1.1 GeV electron beam, a special collimator plate to allow for simultaneous optics measurements, and the low-activity tritium target being prepared for Jefferson Lab. By observing the dependence of the form factor ratio as a function of Q 2 over 0.05–0.09 GeV2 , the dependence of the radii extraction on the shape of the form factors is minimized. As a result, we anticipate the uncertainty of the extracted charge radii difference to be 0.03 fm, a reduction of 70% from the current measurement. Using precise measurements of the 3 He charge radius from isotopic shift or μ He measurements [2–4], we can deduce the absolute 3 H charge radius. The results will provide a direct comparison to recent calculations of the charge radii.

Optical design of laser projection display system by light pipe

According to the characteristics of the laser and its special collimator, we designed a kind of laser projection display system with uniform illumination, using a light pipe as the light homogenization system. The light pipe has several advantages, such as a simple structure, a short period of development, and low cost. The simulation results show that luminous efficiency of the entire illumination system is 78%, and the uniformity is 85%, which reach the designed demands of the optical engine for the laser projection display system.

An inverse method for the design of TIR collimators to achieve a uniform color light beam

Color-over-angle (CoA) variation in the light output of white LEDs is a common and unsolved problem. In this article we introduce a new method to reduce CoA variation using a special collimator. The method is based on analytical inverse design methods. We present a numerical algorithm to solve the differential equations arising from this method and verify the results using Monte Carlo raytracing.

Calibration and features of air-kerma length product meters

Pencil-type air-kerma length product meters are generally used for quality control and radiation exposure measurements in computed tomography. To ensure reliable results, these meters should be calibrated so that measurements are traceable to international standards. Suitable calibration procedures, together with the properties of these meters, were examined and compared with the international standards and recommendations. The calibration procedure and setup used in this study were slightly modified compared with international recommendations. The special collimator system was found to cause less scatter than similar setups in earlier studies. The energy dependence of the meter response was investigated for several types of meters with standard radiation qualities. With most tested meter types, the total variation due to energy dependence was <4 %, but some had strong energy dependence and the variation was up to 15 % or higher. This highlights the importance of a proper calibration. The response of one semiconductor meter type varied up to 8 % when rotating the meter around its axis; this should be taken into account when making calibrations with a static setup.

Estimation of Fan Beam and Parallel Beam Parameters in a Wire Mesh Design

Special collimators used in imaging systems play an important part in obtaining qualified images to improve diagnosis in medicine. The primary aim of this study was to compare resolution between fan beam and parallel beam collimators using Monte Carlo simulation in the shape of cubic holes. Also, parameters such as geometric efficiency, geometric resolution, scatter, penetration, and full width at half maximum were studied to compare their special characteristics. The simulation results demonstrated that the geometry efficiency of a fan beam collimator increased as the angle of the slant hole increased, and the geometric resolution decreased as the angle of the slant hole increased, at a distinct distance from a monoenergetic source of γ-rays. In contrast, at a distinct angle, geometric resolution increased as the distance between the source and the collimator surface increased. For both collimators, scatter and penetration decreased as the distance increased. These results were in agreement with ADAC company data. Finally, fan beam collimators were found to have better resolution than parallel beam collimators with a cubic hole shape in a wire mesh design. Estimation of the fan beam by parallel beam parameters as cubic holes can be suitable in collimator design to improve resolution and efficiency.

MULTI-REFRACTION WITH SAME POLARIZATION STATE IN TWO DIMENSIONAL TRIANGULAR PHOTONIC CRYSTALS

Multi-refraction efiects with one polarization in a two- dimensional triangular photonic crystal (PhC) were systematically studied by theoretical analysis and numerical simulation. The more complicated refraction behaviors can be excited in the higher band regions based on the intricate undulation of one band or the overlap of difierent bands. A novel non-handedness efiect is proposed for the flrst time with group velocity perpendicular to phase velocity. Furthermore, triple refraction phenomena and special collimation efiects of symmetrical positive-negative refraction with the loose incident conditions have been found in difierent band regions of this PhC. These unique features will provide us with more understanding of electromagnetic wave propagation in PhCs and give important guideline for the design of new type optical devices.

SU‐E‐T‐318: Using Monte Carlo in the Design of Small Animal Irradiator Collimators

Purpose: For preclinical research using small animals, a dedicated image‐guided irradiation system has been developed with CBCT imaging and conformal radiation delivery capabilities. A special collimator for a rat model of radiation induced heart disease is desirable. This study aims to design a new primary and secondary collimator system using a Monte Carlo based code. Methods: At an SSD of 32.5 cm, the required maximum field size (FWHM) at 1.0 cm depth in water was 2.0 cm, which is comparable to the size of a normal ratˈs heart. For simulations, we installed the BEAMnrc (GUI version, revision 2.0) and Dosxyznrc (GUI version, revision 1.1) Monte Carlo based codes on a 64 bit Intel quad‐core processor 8×2.0 GHz running the Linux operating system. The simulation model included the X‐ray tube (225kVp), with a Be inherent filter, an external Cu filter (0.5 mm thick), brass primary and secondary collimators and a 10×10×10 cm3 solid water phantom. 1) We began with a simple geometrical design, 2) we expanded the aperture of the primary collimator for the desired FWHM of the beam, and 3) we trimmed the beam by reducing the aperture size of the bottom part of the secondary collimator to eliminate low energy photons and sharpen the penumbra. Results: Monte Carlo simulations successfully accomplished a beam 2.0 cm (FWHM) in diameter at 1.0 cm depth with a sharp penumbra. A new collimator will be constructed based on the final simulated design. We will then verify the Monte Carlo generated depth dose distribution and dose profiles. Conclusions: Monte Carlo based modeling is an effective tool to create new designs for small animal conformal radiotherapy systems. The Beamnrc and Dosxyznrc codes will also be utilized further as the treatment planning engine for the localized heart irradiation project.

Applications of Microstructured Silicon Wafers as Internal Reflection Elements in Attenuated Total Reflection Fourier Transform Infrared Spectroscopy

A novel internal reflection element (IRE) for attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectral acquisition is introduced and applied for several surface-sensitive measurements. It is based on microstructured double-side-polished (100) silicon wafers with v-shaped grooves of {111} facets on their backside. These facets of the so-called "microstructured single-reflection elements" (mSRE) are formed by a crystal-oriented anisotropic wet etching process within a conventional wafer structuring process. They are used to couple infrared radiation into and out of the IRE. In contrast to the application of the commonly used silicon multiple-reflection elements (MRE), the new elements provide single-reflection ATR measurements at the opposite wafer side by using simple reflection accessories without any special collimation. Due to the short light path, the spectral range covers the entire mid-infrared region with a high optical throughput, including the range of silicon lattice vibrations from 300 to 1500 cm(-1). In addition to typical ATR applications, i.e., the measurement of bulk liquids and soft materials, the new reflection elements can be effectively used and customer-specifically designed for in situ and ex situ investigations of aqueous solutions, thin films, and monolayers on Si. Examples presented in this article are in situ etching of native as well as thermal SiO(2) and characterization of polydimethylsiloxane (PDMS) films on Si under various measuring conditions.

A concept for the modernization of a SANS instrument at the IBR-2M pulsed reactor

We consider a new configuration for a neutron small angle scattering instrument at the pulsed IBR-2M reactor with a mixed (cold and thermal) moderator system. This system provides added-up spectra from the cold and thermal parts of the moderator. We have installed the spectrometer using a special collimation system formed by two parts: primary with neutron optics element (divergent neutron guide) and secondary (installed after the divergent neutron guide) with a multiple pinhole collimation system. Our efforts have the goal to obtain smaller Qmin values (as well as higher resolution) with the possibilities to take advantage of an increased neutron flux compared with the present SANS spectrometer in the limited beam hall size. The Monte Carlo simulations will be used to choose and optimize the spectrometer and extraction system using VITESS software package.

WE‐D‐201B‐04: Advances in Instrumentation and Techniques for Quantitative Myocardial Perfusion SPECT

Myocardial perfusion (MP) SPECT (single‐photon emission computed tomography) is a leading diagnostic tool for cardiovascular disease. Its continued importance and popularity have been fueled by new advances in instrumentation and image reconstruction and processing methods. Quantitative three‐dimensional (3D) image reconstruction methods that model the counting statistics in the acquired data and the physics of the imaging process have been widely adopted in clinical practice. They provide improved reconstructed image noise and accurate compensation of image degrading factors including collimator‐detector blur, and photon attenuation and scatter in the patient resulting in significant improvement in both the quality and quantitative accuracy of MP SPECT images. Extension of the quantitative 3D image reconstruction method to four‐dimensional (4D) has been shown to benefit 4D gated MP SPECT. Special collimators designed to provide both improved spatial resolution and increased detection efficiency have been developed and implemented on conventional SPECT systems for application to MP SPECT. The need to provide accurate attenuation compensation and anatomical correlation with MP information for individual patient has resulted in the development of multimodality SPECT/CT systems which have become standard system configuration. More recently, dedicated cardiac SPECT and SPECT/CT systems have emerged in the market place that hold great promise to advance MP SPECT a big step forward. The presentation will describe the basic principles of quantitative 3D and 4D image reconstruction methods. Advances in special collimation and SPECT/CT system designs for MP SPECT will be presented. The improvement in image quality and quantitative accuracy will be demonstrated by simulated, experimental phantom and clinical images.Learning Objectives:1. Describe the basic principles of quantitative 3D and 4D image reconstruction methods that have led to significant improved quality and quantitative accuracy of 3D and 4D gated myocardial perfusion and SPECT images.2. Describe the recent advances in instrumentation for improve myocardial perfusion SPECT.3. Demonstrate the advances using simulated, experimental phantom and clinical MP SPECT images.

Monitoring system for isolated limb perfusion based on a portable gamma camera

The treatment of malignant melanoma or sarcomas on a limb using extremity perfusion with tumour necrosis factor (TNF-alpha) and melphalan can result in a high degree of systemic toxicity if there is any leakage from the isolated blood territory of the limb into the systemic vascular territory. Leakage is currently controlled by using radiotracers and heavy external probes in a procedure that requires continuous manual calculations. The aim of this work was to develop a light, easily transportable system to monitor limb perfusion leakage by controlling systemic blood pool radioactivity with a portable gamma camera adapted for intraoperative use as an external probe, and to initiate its application in the treatment of MM patients. A special collimator was built for maximal sensitivity. Software for acquisition and data processing in real time was developed. After testing the adequacy of the system, it was used to monitor limb perfusion leakage in 16 patients with malignant melanoma to be treated with perfusion of TNF-alpha and melphalan. The field of view of the detector system was 13.8 cm, which is appropriate for the monitoring, since the area to be controlled was the precordial zone. The sensitivity of the system was 257 cps/MBq. When the percentage of leakage reaches 10% the associated absolute error is +/-1%. After a mean follow-up period of 12 months, no patients have shown any significant or lasting side-effects. Partial or complete remission of lesions was seen in 9 out of 16 patients (56%) after HILP with TNF-alpha and melphalan. The detector system together with specially developed software provides a suitable automatic continuous monitoring system of any leakage that may occur during limb perfusion. This technique has been successfully implemented in patients for whom perfusion with TNF-alpha and melphalan has been indicated.

Scatter radiation in cephalometric radiography: the effects of grid and collimation

To measure the scatter fraction in cephalometric radiography with and without a grid and to estimate the patient's dose reduction by using a specially fabricated collimator without a grid. A 16 cm thick water-equivalent phantom was used to measure the scatter fraction. The projection geometry was the same as our conventional one, i.e. the distance from the X-ray source to the centre of the phantom was 200 cm. A photostimulable phosphor plate was used as an X-ray sensor and was 20 cm from the centre of the phantom. The measurements were performed in four combinations: with an antiscatter grid in place, with a specially fabricated collimator in place, with neither in place, and with both in place. The images of a human dried skull were obtained by using the above parameters and were subjectively assessed for a visibility of several reference points. The scatter fraction in the regularly collimated geometry with the antiscatter grid in place was 0.35 for a relative exposure of 1. With the antiscatter grid removed, the scatter fraction increased to 0.68, but the relative exposure was reduced to 0.3. With a special collimator, the scatter fraction was reduced to some extent in all instances, but the exposure was reduced to 0.45. The visibility of the reference points was acceptable in all conditions. In cephalometric radiography, removal of the antiscatter grid yields a significant reduction in exposure with no significant loss of information.

Mass spectrometric study of the oxygen potential at the UO 2− x–U(l) phase limit

Activity measurements of UO 2 at the phase boundary U(l)–UO 2− x have been performed by high temperature mass spectrometry in order to solve discrepancies observed in earlier works. The direct measurement of the UO 2 activity was performed using the multiple Knudsen cell method and a special collimation device in order to (i) circumvent any usual calibration methods (ii) discard any earlier observed parasitic contributions in this system. The oxygen potential is then directly calculated on the basis of pure UO 2(s) accurate thermodynamic data for the diphasic U(l)–UO 2− x domain in the 2000–2250 K range.

High resolution SPECT in small animal research.

Single Photon Emission Computed Tomography (SPECT) is a technique used to assess physiological and biochemical processes under in vivo conditions. SPECT generates tomographic images from blood flow, glucose metabolism and receptor characteristics using radioactively labelled substances. This paper reviews the state of the art of in vivo imaging of laboratory animals in modified human and dedicated animal SPECT scanners. SPECT cameras with special collimators currently reach spatial resolutions up to 1 mm and sensitivities of about 1000 cps/MBq, allowing observation of receptor activity concentration changes in the pico-mole range. The time resolution of such cameras strongly depends on the pharmacological behaviour of the tracer and can range from several minutes to hours. Within these limits the functional characterization of many processes is possible. SPECT also offers the possibility to set up dynamic study protocols and repeated measurements of the same animal. This technique reduces the need for sacrificing animals, as was commonly practiced before the development of animal cameras. Animal SPECT gives the opportunity to monitor physiological and biochemical processes in animals in vivo, without interfering with the system under observation, and may become a valuable adjunct to the instrumentation (autoradiography, in vitro methods) of animal research.

New Pressure Domain in Single Crystal X-ray Diffraction Using a Sealed Source.

The pressure range of single crystal structure determination using a sealed source was extended to over 30 GPa with the improved techniques in this study. Rare gas solid helium was found to be the only pressure medium that can secure hydrostatic environment to very high pressure. The solid argon or neon induces significant divitoric stresses in crystals at relatively low pressure. The crystal volume was doubled at certain targeting pressure by using a new gasket material. The intrinsic background of a pressure cell was significantly reduced by a special collimator. These procedures improved the signal/noise ratio to 3 - 4 times. The quality of the structure refinement and the accuracy of atomic coordinates at 33 GPa are comparable with measurements at ambient conditions in a diamond cell.

Calibration of radiometers for remote sensing of the Earth's atmosphere from space

Two models of spaceborne radiometers for measuring atmospheric radiation at the Earth's limb radiance profiles have been designed in Estonia and used aboard several Russian orbital stations from 1971 to 1993. Calibration was carried out with a Teflon flat-plate diffuser and a DXW lamp traceable to the National Institute of Standards and Technology (NIST) and an integrating sphere with a 1,2 m diameter and an 0,4 m aperture. The absolute spectral radiance of the aperture was determined by comparison with a tungsten ribbon standard lamp, calibrated at the All-Russian Research Institute for Optophysical Measurements (VNIIOFI), Moscow. The field-of-view responsivity was investigated by using a special collimator facility. The following characteristics of the spaceborne radiometers were determined: absolute responsivity constant, spectral characteristics, field-ofview responsivity and off-axis rejection, amplitude transfer function (nonlinearity) and temperature dependence of responsivity. The in-flight checking of long-term responsivity changes was carried out by using internal reference lamps and radiation from the Moon and the Sun.