Grid Strip Research Articles

A comprehensive assessment of a prototype high ratio antiscatter grid in interventional cardiology using experimental measurements and Monte Carlo simulations

Objective. To assess the performance of a new antiscatter grid design in interventional cardiology for image quality improvement and dose reduction using experimental measurements and Monte Carlo (MC) simulation. Approach. Experimental measurements were performed on an angiography system, using a multi-layered tissue simulating composite phantom made from of poly(methyl methacrylate), aluminium and expanded polystyrene (2/0.2/0.7 cm). The total phantom thickness ranged from 20.3 cm to 40.6 cm. Four conditions were compared; (A) 105 cm source-image receptor distance (SID) without grid, (B i) 105 cm SID with grid ratio (r) and strip density (N) (r15N80), (B ii) 120 cm SID without grid, and (Biii) 120 cm SID with high ratio grid (r29N80). The system efficiency (η), defined by the signal-to-noise ratio, was compared from the B conditions against case A. These conditions were also simulated with MC techniques, allowing additional phantom compositions to be explored. Weighted image quality improvement factor (ηw (u)) was studied experimentally at a specific spatial frequency due to the SID change. Images were simulated with an anthropomorphic chest phantom for the different conditions, and the system efficiency was compared for the different anatomical regions. Main results. Good agreement was found between the η and ηw (u) methods using both measured and simulated data, with average relative differences between 2%–11%. Case B iii provided higher η values compared to A, and B i for thicknesses larger than 20.3 cm. In addition, case B iii also provided higher η values for high attenuating areas in the anthropomorphic phantom, such as behind the spine. Significance. The new antiscatter grid design provided higher system efficiency compared to the standard grid for the parameters explored in this work.

Removing grid artifacts from a two-dimensional crisscrossed grid in cone-beam computed tomography to enhance image quality

One-dimensional linear X-ray grids are typically used in clinical practice to reduce the number of scattered X-rays reaching the detector surface, thus improving image contrast in radiography. However, such grids can only remove scattered X-rays in one direction. Additionally, the primary challenge in using X-ray grids in digital radiography is the presence of grid artifacts, such as grid strip shadows and moiré, which can reduce image quality. To overcome these difficulties, in this study, we developed a prototype two-dimensional (2D) crisscrossed grid with a strip density of 1.724 lines/mm by adopting a high-precision sawing process to further improve its scatter radiation removal ability and implemented it in a cone-beam computed tomography (CBCT) system to enhance image quality. We propose a new software-based method called the grid artifact reduction (GAR) algorithm to efficiently eliminate grid artifacts of a 2D grid in CBCT. The GAR algorithm involves three main steps: 1) preprocessing for flat-field compensation, 2) postprocessing for GAR, and 3) CBCT reconstruction. To verify the efficacy of the proposed approach, we conducted an experiment on a CT quality control phantom (Pro-CT MK II™) and quantitatively evaluated the CBCT image quality using the contrast-to-noise ratio (CNR) and Hounsfield unit (HU) accuracy error. The CNR value measured in the CBCT image obtained using the 2D grid and proposed GAR algorithm was 3.22, which is approximately 4.4 times of the value obtained without GAR. Furthermore, the corresponding HU accuracy error was 30.47, an improvement of approximately 1.3 times. These results indicate that the proposed approach is highly efficient in eliminating scattered X-rays, thereby improving the quality of CBCT images. Consequently, high-quality CBCT images were obtained using the proposed approach (i.e., using a 2D crisscrossed grid in CBCT and the proposed GAR algorithm).

Probabilistic comparison of gray and white matter coverage between depth and surface intracranial electrodes in epilepsy

In this study, we quantified the coverage of gray and white matter during intracranial electroencephalography in a cohort of epilepsy patients with surface and depth electrodes. We included 65 patients with strip electrodes (n = 12), strip and grid electrodes (n = 24), strip, grid, and depth electrodes (n = 7), or depth electrodes only (n = 22). Patient-specific imaging was used to generate probabilistic gray and white matter maps and atlas segmentations. Gray and white matter coverage was quantified using spherical volumes centered on electrode centroids, with radii ranging from 1 to 15 mm, along with detailed finite element models of local electric fields. Gray matter coverage was highly dependent on the chosen radius of influence (RoI). Using a 2.5 mm RoI, depth electrodes covered more gray matter than surface electrodes; however, surface electrodes covered more gray matter at RoI larger than 4 mm. White matter coverage and amygdala and hippocampal coverage was greatest for depth electrodes at all RoIs. This study provides the first probabilistic analysis to quantify coverage for different intracranial recording configurations. Depth electrodes offer increased coverage of gray matter over other recording strategies if the desired signals are local, while subdural grids and strips sample more gray matter if the desired signals are diffuse.

A chiral metamaterial with high reflectance for antenna applications

AbstractIn this article, a chiral metamaterial (CMM) with high reflectance is constructed by using both the S‐shaped strip and the grid strip. Numerical simulation results reveal that the reflectance reaches 0.7 and the transmitted wave is converted from y‐polarization to left‐hand circular polarization. Therefore, the proposed CMM has the function of polarized transformation from linear polarization (LP) wave to circular polarization (CP). In addition, a Fabry‐Perot resonator cavity‐like behavior is found in the CMM itself. We design and measure a CP CMM‐based Fabry‐Pérot resonator cavity antenna. A bandwidth of 13.25% (|S11| < −10 dB, AR < 3 dB, and peak gain drop<3 dB) and a peak gain of 14.76 dBic are attained. The proposed antenna has potential applications in advanced nanosatellite communication systems.

The determination of the optimal strip‐thickness of anti‐scatter grids for a given grid ratio and strip height

AbstractIn X‐ray imaging, anti‐scatter grids are used to reduce scatter radiation reaching image receptors, hence improving image quality. Optimization of grid performance is essential for improving image diagnostic quality and minimizing radiation doses to patients. This work investigated the performance of a series of grid designs modeled from the design of typically focused grid with grid ratio 8:1 (r8) and strip height 1.7 mm (h1.7) for high‐energy radiographic applications. Monte Carlo simulation was used to evaluate designs (r8h1.7) which had the strip thickness changed from 6 to 150 μm in 2 μm increments and the interspace distance fixed at 214 μm. The transmissions of radiation in grid materials were modeled by using a regression with radial‐basis‐function‐networks (RBFNS). KSNR was then determined from RBFNS models of radiation transmissions. The optimal strip‐thickness was obtained at the maximum signal‐to‐noise ratio (SNR) improvement factor (KSNR). For high‐energy applications at 100 peak‐kilo‐voltage (kVp) and 30 cm PMMA thickness, the optimal lead‐strip‐thickness was found approximately 74 μm resulting in a strip‐frequency approximately 35 per cm (N35). Using the optimal thickness for imaging condition at 100 kVp and 30 cm thickness, the KSNR would increase by approximately 5.3%. This work showed the existence of optimal strip‐thickness for a series of grids with a given grid‐ratio, strip‐height, strip‐, and interspace materials. The findings are useful and provide guidance to improve grid designs for better performance that will essentially lead to better image quality and better radiation protection for patients.

Friction and local pressure loss characteristics of a 5 × 5 rod bundle with spacer grids

This paper presents the experimental results and analyses of the friction and local pressure loss coefficient of a 5 × 5 rod bundle with spacer grid. Based on the experimental data, friction and local pressure loss models were assessed and the role of spacer grid was discussed. The results showed that Cheng and Todreas model could predict bare rod friction loss well, and Chun model applied for high Re but would severely underestimate grid local loss for small Re. For two-phase condition, a universal correlation was proposed for bare rod two-phase friction multiplier, and it was found that all existing models cannot predict grid local loss multiplier very well. High prediction accuracy could be obtained by combining homogenous flow model, the liquid-mixture density ratio and a modification factor as a function of the grid parameter ε (axial projected area of grid strip to flow area) and void fraction.

Evaluation of high grid strip densities based on the moiré artifact analysis for quality assurance: Simulation and experiment

We have recently developed precise x-ray grids having strip densities in the range of 100 – 250 lines/inch by adopting the precision sawing process and carbon interspace material for the demands of specific x-ray imaging techniques. However, quality assurance in the grid manufacturing has not yet satisfactorily conducted because grid strips of a high strip density are often invisible through an x-ray nondestructive testing with a flat-panel detector of an ordinary pixel resolution (>100 μm). In this work, we propose a useful method to evaluate actual grid strip densities over the Nyquist sampling rate based on the moiré artifact analysis. We performed a systematic simulation and experiment with several sample grids and a detector having a 143-μm pixel resolution to verify the proposed quality assurance method. According to our results, the relative differences between the nominal and the evaluated grid strip densities were within 0.2% and 1.8% in the simulation and experiment, respectively, which demonstrates that the proposed method is viable with an ordinary detector having a moderate pixel resolution for quality assurance in grid manufacturing.

Indirect measurement of high grid strip densities over Nyquist sampling rate based on the moiré pattern analysis for quality assurance in grid manufacturing

Abstract We have recently developed very precise carbon-interspaced antiscatter grids having a wide range of grid strip densities ( i.e. , 85–234 lines/in.) by adopting the sawing process, depending on the demands of specific imaging modalities. However, because grid strips of the recently developed grids are mostly invisible through X-ray nondestructive testing due to their high strip densities, quality assurance in the manufacturing has not yet satisfactorily made. In this work, we proposed a pragmatic method to measure actual grid strip densities over the Nyquist sampling rate based on the moire pattern analysis. We prepared several samples of the carbon-interspaced grids having nominal grid strip densities of 85, 103, 130, 150, 178, 203, 215, and 234 lines/in. and measured their strip densities by using the proposed method to demonstrate its viability assessment. The differences between the nominal and the measured grid strip densities were less than about 1.8%, indicating the proposed method is useful for the quality assurance in grid manufacturing.

Investigation of proper imaging conditions in the moving grid technique for a reduction of grid line artifacts

The most critical problem remaining as an obstacle for the successful use of antiscatter grids in digital X-ray imaging is probably the observation of grid line artifacts such as moire patterns and shadows of the grid strips themselves in X-ray images, resulting in a risk of misdiagnosis by physicians. In this paper, in order to find a practical solution to the problem of grid line artifacts, we revisited the moving grid technique and investigated its proper imaging conditions. We implemented a simple and useful moving-grid analysis code, iTOM ™ , and performed systematic simulations for a theoretical analysis. We also performed experiments and compared the results to the simulated ones to demonstrate the effectiveness of the code. According to our simulation and experimental results, the grid line artifacts can be effectively reduced when the grid moves with a large velocity or with specific velocities that reduce the coefficient of variation (CV), even with a small velocity. These velocities are determined by using the related parameters such as the grid pitch, the grid strip width, and the exposure time.

Research of mechanical characteristics of pb-ca-sn alloys and tapes for cur-rent leads in sealed lead-acid batteries (Vrla)

Purpose. The modern trend in lead-acid battery industry is the changeover to reliable and safe leak-proof VRLA batteries. However, the properties of grid alloys of these batteries are still insufficiently studied, that hampers application of these batteries at railway transport. The purpose of this work is the research of dependence of mechanical properties of grid alloys on temperature conditions of casting, deformation of rolling and ageing time. Methodology. Mechanical properties of alloys and grids have been defined at standard tensile testing machine R-0,5. Findings. The rolling of lead-calcium alloys with deformation more than 90% raises their durability and reduces their plasticity. When rising the temperature of the casting moulds (in range 60-170°С) the durability of lead-calcium and lead-antimony alloys decreases, and the plasticity increases, that are mostly evident for PbCa0.1Sn0.3 alloy, and least of all – for PbCa0.05Sn1.1 alloy. Durability of lead-calcium and lead-antimony alloys increases and plasticity decreases with increasing the time of ageing: this is mostly evident for alloy PbCa0.05 Sn1.1 and strips made from it. Originality. It was determined that decrease of alloys overcooling at crystallization results in drop of their durability and increase of plasticity. The composition and structure of alloys strongly influence dynamics of their ageing. Practical value. It is proposed by authors: a) to increase the temperature of crystallization of alloy for negative grid strip to 120-160°С instead of 80-120°С, that will raise plasticity of strip and reduce deterioration of the equipment; b) to replace PbSb1.8Se alloy of cast grids by PbCa0.1Sn0.3 alloy, that will allow reducing weight of grids by 25 % at the same durability; c) to increase range of ageing of grids cast from PbCa0.1Sn0.3 alloy to 3-30 days that reduces the production costs. It’s all taken together will reduce deterioration of the process equipment and cut down production cost at conservation of characteristics of production.

Stochastic Behavior of Phase Synchronization Index and Cross-Frequency Couplings in Epileptogenic Zones during Interictal Periods Measured with Scalp dEEG

The stochastic behavior of the phase synchronization index (SI) and cross-frequency couplings on different days during a hospital stay of three epileptic patients was studied for non-invasive localization of the epileptogenic areas from high density, 256-channel, scalp EEG (dEEG) recordings. The study was performed with short-duration (0–180 s), seizure-free, epileptiform-free, and spike-free interictal dEEG data on different days of three subjects. The seizure areas were localized with subdural recordings with an 8 × 8 macro-electrode grid array and strip electrodes. The study was performed in theta (3–7 Hz), alpha (7–12 Hz), beta (12–30 Hz), and low gamma (30–50 Hz) bands. A detrended fluctuation analysis was used to find the long range temporal correlations in the SI that reveals the stochastic behavior of the SI in a given time period. The phase synchronization was computed after taking Hilbert transform of the EEG data. Contour plots were constructed with 20 s time-frames using a montage of the layout of 256 electrode positions. It was found that the stochastic behavior of the SI was higher in epileptogenic areas and in nearby areas on different days for each subject. The low gamma band was found to be the best to localize the epileptic sites. Also, a stable higher pattern of SI emerged after 60–120 s in the epileptogenic areas. The cross-frequency couplings of SI in theta–gamma, beta–gamma, and alpha–gamma bands were decreased and spatial patterns were fragmented in epileptogenic areas. Combinations of an increase in the stochastic behavior of the SI and decrease in cross-frequency couplings are potential markers to assist in localizing epileptogenic areas. These findings suggest that it is possible to localize the epileptogenic areas non-invasively from a short-duration (∼180 s), seizure-free and spike-free interictal scalp dEEG recordings.

Study of a Novel MEMS Accelerometer with Low Noise Reduced by Actuators

A novel MEMS (Micro Electronic Mechanical System) capacitive accelerometer is presented, which is mainly composed of supporting beam, seismic mass, grid strip capacitances, comb capacitances and electrostatic driver. The damping of grid strip capacitances with variable overlapping area is mainly affected by the slide film air damping, which is small and neglectful, and the damping between comb capacitor is squeeze film air damping. The comb sensing gap can be reduced by electrostatic actuators by which the aspect ratio can reach to 75:1 which greatly depress the limitation of DRIE (Deep reactive ion etching) process on high aspect ratio, and the initial sensing capacitance increases from 2.97 pf to 14.87 pf. The squeeze film damping is reduced from 0.046 Nm/s to 0.0015 Nm/s by designing the comb-shaped grooves on the fixed comb electrodes. The comb initial sensing gap is optimized according to formation factors of system noise, and the noise is reduced from 1.395 μg/√HZ to 0.591 μg/√HZ. The simulation results show that the accelerometer sensitivity achieves 8.40 pf/g, which is two times of the conventional devices.

Vitrification of mouse embryos using the thin plastic strip method

ObjectiveThe aim of this study was to compare vitrification optimization of mouse embryos using electron microscopy (EM) grid, cryotop, and thin plastic strip (TPS) containers by evaluating developmental competence and apoptosis rates.MethodsMouse embryos were obtained from superovulated mice. Mouse cleavage-stage, expanded, hatching-stage, and hatched-stage embryos were cryopreserved in EM grid, cryotop, and TPS containers by vitrification in 15% ethylene glycol, 15% dimethylsulfoxide, 10 µg/mL Ficoll, and 0.65 M sucrose, and 20% serum substitute supplement (SSS) with basal medium, respectively. For the three groups in which the embryos were thawed in the EM grid, cryotop, and TPS containers, the thawing solution consisted of 0.25 M sucrose, 0.125 M sucrose, and 20% SSS with basal medium, respectively. Rates of survival, re-expansion, reaching the hatched stage, and apoptosis after thawing were compared among the three groups.ResultsDevelopmental competence after thawing of vitrified expanded and hatching-stage blastocysts using cryotop and TPS methods were significantly higher than survival using the EM grid (p<0.05). Also, apoptosis positive nuclei rates after thawing of vitrified expanded blastocysts using cryotop and TPS were significantly lower than when using the EM grid (p<0.05).ConclusionThe TPS vitrification method has the advantages of achieving a high developmental ability and effective preservation.

Characteristics of a novel biaxial capacitive MEMS accelerometer

A novel MEMS accelerometer with grid strip capacitors is developed. The mechanical and electrical noise can be reduced greatly for the novel structure design. ANSOFT-Maxwell software was used to analyze the fringing electric field of the grid strip structure and its effects on the designed accelerometer. The effects of the width, thickness and overlapping width of the grid strip on the sensing capacitance are analyzed by using the ANSOFT-Maxwell software. The results show that the parameters have little effect on the characteristics of the presented accelerometer. The designed accelerometer was fabricated based on deep RIE and silicon–glass bonding processes. The preliminary tested sensitivities are 0.53 pF/g and 0.49 pF/g in the x and y axis directions, respectively. A resonator with grid strip structure was also fabricated whose tested quality factor is 514 in air, which proves that the grid strip structure can reduce mechanical noise.

A novel capacitive micro-accelerometer with grid strip capacitances and sensing gap alterable capacitances

The comb capacitances fabricated by deep reactive ion etching (RIE) process have high aspect ratio which is usually smaller than 30: 1 for the complicated process factors, and the combs are usually not parallel due to the well-known micro-loading effect and other process factors, which restricts the increase of the seismic mass by increasing the thickness of comb to reduce the thermal mechanical noise and the decrease of the gap of the comb capacitances for increasing the sensitive capacitance to reduce the electrical noise. Aiming at the disadvantage of the deep RIE, a novel capacitive micro-accelerometer with grid strip capacitances and sensing gap alterable capacitances is developed. One part of sensing of inertial signal of the micro-accelerometer is by the grid strip capacitances whose overlapping area is variable and which do not have the non-parallel plate's effect caused by the deep RIE process. Another part is by the sensing gap alterable capacitances whose gap between combs can be reduced by the actuators. The designed initial gap of the alterable comb capacitances is relatively large to depress the effect of the maximum aspect ratio (30 : 1) of deep RIE process. The initial gap of the capacitance of the actuator is smaller than the one of the comb capacitances. The difference between the two gaps is the initial gap of the sensitive capacitor. The designed structure depresses greatly the requirement of deep RIE process. The effects of non-parallel combs on the accelerometer are also analyzed. The characteristics of the micro-accelerometer are discussed by field emission microscopy (FEM) tool ANSYS. The tested devices based on slide-film damping effect are fabricated, and the tested quality factor is 514, which shows that grid strip capacitance design can partly improve the resolution and also prove the feasibility of the designed silicon-glass anodically bonding process.

Simultaneous optimisation of the properties of engineered composite grids for lead-acid batteries

We have developed innovative multilayer composite grids as engineered materials, which are produced in the form of grid strip in a single, highly efficient, multistage electrodeposition process. In the present paper, we are reporting, how the individual requirements for grid properties can be satisfied and optimised individually and then combined simultaneously to an overall optimum in this new family of composite grid materials. The multilayer composite materials are composed of different layers of different structures and properties, which can provide a combination of different functional properties to satisfy a more demanding total specification of mechanical behaviour, electrical performance, corrosion resistance and cycling behaviour. The paper deals with the improvement of these properties in detail and with the overall simultaneous engineering of the grid material.

Technical and economic advantages of making lead−acid battery grids by continuous electroforming

A new continuous electroforming process to manufacture lead grids for automotive and industrial lead−acid batteries has been developed. A galvanic cell comprising a drum cathode for electroforming and a subsequent series of galvanic cells which form a strip galvanizing line are operating in a single, fully continuous, automatic process. Virgin lead or lead scrap may be used as the anode material. The product is grid strip of any specified thickness and design which can be fed into existing strip-pasting equipment. The composition and microstructure of the grid material can be varied to provide increased corrosion resistance and increased paste adherence. A unique feature of the material is its inherent layered composite structure that allows optimization of the properties according to particular functional requirements. Thus, both the specific power and the specific energy of the battery can be increased by reducing weight. The material properties increase the calendar life of the battery by increasing the corrosion resistance of the grid, and increase the cycle-life of the battery by improved adherence of the positive active material. The technical and economic features and competitive advantages of this new technology and product are presented in quantitative terms.

A PARALLEL CELL-BY-CELL AMR METHOD FOR THE PPM HYDRODYNAMICS CODE

The Piecewise Parabolic Method (PPM) hydrodynamics code and other codes based on the PPM technique have been used extensively for the simulation of astrophysical phenomena. A new version of the PPM hydrodynamics code under development at the Laboratory for Computational Science and Engineering (LCSE) at the University of Minnesota is described. This new code incorporates a version of dynamic local adaptive mesh refinement (AMR) targeted specifically at improving the treatment of shocks and contact discontinuities. This AMR technique is not intended to increase grid resolution in entire regions of the problem for which standard techniques of nonuniform grids and simple grid motion are adequate. Because the AMR is targeted at surfaces within a flow that can develop complex shapes, a cell-by-cell approach to the grid refinement is adopted in order to minimize the number of refined grid cells, with the hope of controlling the computational cost. As a result of this approach, the number of refined cells needed across a given shock or captured contact discontinuity is modest (&lt; 10). Because the PPM method is very complex, ordinarily its wide difference stencil demands that a relatively large number of extra grid cells need to be added to each end of a grid strip, even when adapting to a thin feature of the flow. To avoid the work associated in handling these extra cells, only to conveniently produce valid data in the thin strip of actual interest, we have used intermediate results of the coarse grid calculation in order to eliminate the need for all but two of these extra cells at each end of the refined grid strip. The benefits of this approach will be described through sample results in 2D, and the method for handling the boundaries of the refined grid strips efficiently will be discussed. The data structures in this method are being carefully designed to permit efficient implementation of the algorithm on clusters of shared memory machines, with automatic dynamic balancing of computational loads over the cluster members.

A Monte Carlo study of grid performance in diagnostic radiology: task-dependent optimization for digital imaging

A Monte Carlo computational model has been used to optimize grid design in digital radiography. The optimization strategy involved finding grid designs that, for a constant signal-to-noise ratio, resulted in the lowest mean absorbed dose in the patient. Different examinations were simulated to explore the dependence of the optimal scatter-rejection technique on the imaging situation. A large range of grid designs was studied, including grids with both aluminium and fibre interspaces and covers, and compared to a 20 cm air gap. The results show that the optimal tube potential in each examination does not depend strongly on the scatter-rejection technique. There is a significant dose reduction associated with the use of fibre-interspaced grids, particularly in paediatric radiography. The optimal grid ratio and strip width increase with increasing scattering volume. With increasing strip density, the optimal strip width decreases, and the optimal grid ratio increases. Optimal grid ratios are higher than those used today, particularly for grids with large strip density. It is, however, possible to identify grids of good performance for a range of strip densities and grid ratios provided the strip width is selected accordingly. The computational method has been validated by comparison with measurements with a caesium iodide image receptor.

Investigation of the performance of antiscatter grids: Monte Carlo simulation studies

Monte Carlo methods have been applied to the study of the performance of antiscatter grids in radiography. Photon histories for imaging with a 20 cm thick water phantom irradiated with an 80 kV X-ray spectrum were generated by Monte Carlo simulation. The scattering and absorption of the photons transmitted from the phantom were traced in the grid. Grids were evaluated with strip densities ranging from 10 to 67 lines/cm, grid ratios from 6 to 15, and lead-to-interspace ratios from 1/9 to 1/2. The contrast improvement factor and the Bucky factor were used as the benefit and cost indicators, respectively, for evaluation of the grids. The dependence of these factors on the grid ratio, lead-to-interspace ratio, strip density, lead content, and interspace material was investigated. The results indicate that high-strip-density grids with thin lead strips and high grid ratios can provide higher contrast improvement factors than are achieved with low-strip-density grids, without an increase in patient exposure. This theoretical approach is useful for the prediction and development of optimal antiscatter grids for radiographic procedures.