Air Gap Technique Research Articles

Geant4 Simulation of Scatter Radiation Removal: Comparison and Validation of Anti-scatter Grid and Air Gap for X-ray Mammography

Abstract: X-ray mammography modality provides excellent low-contrast resolution images with low scatter radiation, making it the gold standard in diagnosing breast cancer. Anti-scatter grid and air gap techniques are typically used to further minimize the scatter radiation and improve image quality. Thus, Geant4 simulation was used to investigate the effectiveness of these techniques in removing scatter radiation in X-ray mammography. The effectiveness of an anti-scatter grid was evaluated using the Bucky factor, where it linearly increased with increasing the anti-scatter grid ratio. It was found that increasing the grid frequency affects the Bucky factor depending on the design of the grid ratio. This research proved that designing an anti-scatter grid with high grid frequency (80 lp/mm), low grid ratio (2:1), and proper orientation minimized common anti-scatter grid artifacts. The effectiveness of the air gap technique was also evaluated using the air gap dose factor. It increased non-linearly with increasing magnification. This research validated that using smaller pixel sizes and small focal spot sizes improved spatial resolution with magnification. Our simulation validated that the anti-scatter grid and air gap were effective techniques in removing scatter radiation. By comparing these techniques, the anti-scatter grid was more effective in removing scatter radiation at the expense of increasing the radiation absorbed dose with the exception of 2.0 magnification. It’s recommended to be extremely cautious when using 2.0 magnification or a grid ratio higher or equal to 8:1. These parameters may cause the radiation absorbed dose to be increased by several folds. Keywords: Geant4, Gate, X-ray mammography, Scatter removal, Anti-scatter grid, Air gap.

Additive manufacturing substrate for patch antenna using variable infill Poly Lactic acid

A low dielectric constant substrate for patch antenna using additive manufacturing air gap technique is prepared. This work can tune the desirable value of the dielectric constant and loss tangent of patch substrate by optimizing the various factors involved in 3D printing. The prototype is based on PLA Pro + filament to check the variation in dielectric constant and loss tangent. The performance of the 3D printer used has also been examined for the proposed substrate. This technique helps to create low dielectric constant materials for the high-frequency range of operation of RF communication devices. The prototype's experimental results demonstrate that the 80% Linearly infilled sample (L-80) outperforms the 100% Linearly infilled sample (L-100) in terms of average loss tangent, which has improved by 45.07% on average from 8.5 to 12.5 GHz. At higher frequency ranges of 10.86 to 12.5 GHz, the dielectric constant of the L-80 sample outperforms the L-100 sample in terms of a lower desirable dielectric constant (εr) range (2.0≤εr≤2.2). The dielectric constant results for the above frequency range show that the L-80 sample is 3 to 5 times better than L-100. The average improvement in the dielectric constant for 8.5 to 9.0 GHz is nearly 31.84%.

OPTIMIZACIJA POSEGOV V RADIOLOŠKI TEHNOLOGIJI – SLIKANJE LEDVENE HRBTENICE V SPLOŠNI RADIOLOGIJI

Purpose: Any use of ionizing radiation must be justifi ed and the benefi t must be greater than the harm it causes. Imaging must be performed with the lowest possible dose received by the patient, while maintaining optimal radiographic image quality. Imaging of the lumbar spine is a relatively high dose imaging procedure. This systematic review aims to explore optimisation options to reduce patient exposure, while maintaining radiographic quality during plain lumbar spine imaging. Methods: A systematic review of the literature from the databases Pub Med Central, EBSCOhost including CINAHL, Cochrane Library, Web of Science, Science Direct, DiKUL and Springer Link was conducted. The documents were fully accessible and in the English language. Results: 26 experimental studies were included in the analysis. There are many optimisation methods: changing the tube potential, comparison of diff erent projections, use of shielding, primary beam collimation, increasing the source-to-image receptor distance, compression of the imaged area, using the air gap technique, evaluation of the need for additional projections, and rotating the patient depending on the tube side. On average, the dose is reduced by 44%. Studies that also evaluated the quality of radiographs found all radiographs to be diagnostically acceptable. Conclusion: The results confi rm a reasonable use of methods to optimize radiation exposure and to maintain an optimal image quality of radiographs. A systematic review for each specifi c area in general radiography should be conducted in the future. Keywords: lumbar spine imaging, optimisation, dose reduction, low dose, image quality

Impact of air gap, range shifter, and delivery technique on skin dose in proton therapy.

Side effects of radiation therapy may include skin damage. The surface dose is of great interest and contains the buildup effect. In particular, the proton therapy community requires further experimental data to quantify doses in the surface region. This specification includes the skin dose, which is defined according to ICRU Report No. 39 at 70μm water equivalent depth. The aim of this study is to gather more knowledge of the skin dose by varying key parameters defined by the patient treatment plan. This consists of clinical aspects such as the influence of the air gap, the application of a range shifter (RS), or the proton delivery technique. Skin doses were determined with a PTW 23391 extrapolation chamber with three thin Kapton® entrance windows operated as a conventional ionization chamber. The impact on the skin dose for quasi-monoenergetic pencil beam scanning (PBS) proton beams was evaluated for clinical air gaps between 3.5 and 51.1cm. The differences in skin dose were assessed by irradiating equivalent fields with an RS of 51mm water equivalent thickness (RS51) and without. Furthermore, the delivery techniques PBS, uniform scanning (US), and double scattering (DS) were compared by defining a spread-out Bragg peak (SOBP). TOPAS (V.3.1.2) was used to model an IBA nozzle with PBS and to score dose to water at the surface of a water phantom. For the monoenergetic fields without the application of the RS the skin dose was constant down to an air gap of 6.2cm. A lower air gap of 3.5cm showed a variation in skin dose by up to 2.4% compared to the results obtained with larger air gaps. With the inserted RS51 an increase in the skin dose was found for air gaps smaller than 11.3cm. Experimentally, a dose difference of 1.4% was recorded for an air gap of 6.2cm by inserting an RS and none. With the Monte Carlo calculations the largest dose increase was observed at the air gap of 3.5cm with 1.7% and 4.0% relative to the skin dose results without the RS and to the largest evaluated air gap of 51.1cm, respectively. The SOBP comparison of the beam modalities at the measuring plane at the isocenter revealed higher skin doses without RS (including RS) by up to +1.9% (+1.5%) for DS and +1.3% (+1.1%) for US compared to PBS. For all three techniques an approx. 2% rise in skin dose was observed for the largest evaluated air gap of 37.7cm to an air gap of 6.2cm when using an RS51. The study investigated aspects of skin dose of a water equivalent phantom by varying key parameters of a proton treatment plan. Parameters like the RS, the air gap, and the delivery modality have an impact on the order of 4.0% for the skin dose at the depth of 70μm. The increases in skin dose are the effects of the contribution of the increased electron fluence at small air gaps and the emitted hadronic particles produced by the RS.

High gain antenna at 915 MHz for off grid wireless networks

This paper presents a high gain antenna for off-grid wireless networks at 915 MHz. The requirements for compact size and high gain antenna are needed in the industrial, scientific and medical (ISM) band for better performance and coverage. Hence, microstrip planar substrate is proposed to overcome the size challenges. The proposed antenna is designed based on rectangular patch with air gap technique. The proposed antenna is optimized using computer simulation technology software (CST) and fabricated on low profile FR-4 substrate. The measured performance agreed well with the simulated one. The reflection of less than -10 dB is obtained with high gain of 6.928 dB at desired frequency. Overall, this antenna can be a good candidate for the off-grid wireless network applications.

Air gap technique is recommended in axiolateral hip radiographs.

PurposeTo investigate the replacement of conventional grid by air gap in axiolateral hip radiographs. The optimal air gap distance was studied with respect to radiation dose and image quality using phantom images, as well as 26 patient axiolateral hip radiographs.MethodsThe CDRAD phantom, along with polymethylmethacrylate slabs with thicknesses of 10.0, 14.6, and 20.0 cm was employed. The inverse image quality index and dose area product (DAP), as well as their combination, so called figure‐of‐merit (FOM) parameter, were evaluated for these images, with air gaps from 20 to 50 cm in increments of 10 cm. Images were compared to those acquired using a conventional grid utilized in hip radiography. Radiation dose was measured and kept constant at the surface of the detector by using a reference dosimeter. Verbal consent was asked from 26 patients to participate to the study. Air gap distances from 20 to 50 cm and tube current‐time products from 8 to 50 mAs were employed. Exposure index, DAP, as well as patient height and weight were recorded. Two radiologists evaluated the image quality of 26 hip axiolateral projection images on a 3‐point nondiagnostic — good/sufficiently good — too good scale. Source‐to‐image distance of 200 cm and peak tube voltage of 90 kVp were used in both studies.Results and conclusionBased on the phantom study, it is possible to reduce radiation dose by replacing conventional grid with air gap without compromising image quality. The optimal air gap distance appears to be 30 cm, based on the FOM analysis. Patient study corroborates this observation, as sufficiently good image quality was found in 24 of 26 patient radiographs, with 7 of 26 images obtained with 30 cm air gap. Thus, air gap method, with an air gap distance of 30 cm, is recommended in axiolateral hip radiography.

Reduction of AC Winding Losses Due to Fringing-Field Effects in High-Frequency Inductors With Orthogonal Air Gaps

In high-frequency inductors, ac winding losses are affected by skin and proximity effects, including uneven current distribution due to fringing magnetic fields around air gaps. It is well known that fringing effects can be mitigated using distributed air gaps. This article is focused on an orthogonal air-gap approach, which is a distributed air-gap technique where gaps are placed in core segments parallel with the windings and in core segments perpendicular to the windings. The orthogonal air-gap approach is developed using a one-dimensional analytical framework and validated by two-dimensional and three-dimensional finite-element simulations. Analytical guidelines are presented to optimize the air-gap distribution to achieve minimum ac resistance. As a case study, a planar inductor is designed for an 8-kW SiC-based buck converter operating at 250 kHz. It is shown how the orthogonal air gaps result in approximately 50% reduction in ac resistance and substantially reduced inductor losses compared to the design using standard air gaps. Experimental validation includes measurements of losses on the converter prototype as well as quality factor measurements in a resonant-circuit test setup.

Optimisation of the lateral lumbar spine projection using an air-gap technique

IntroductionLumbar spine radiography is considered as having a high radiation dose compared to other planar radiography examinations. The aim of this study was to investigate the feasibility of replacing an antiscatter grid with an air gap technique to achieve dose reduction for lateral lumbar spine radiography while maintaining image quality on a direct digital radiography (DDR) system. MethodsIn phase 1, an experimental study using an anthropomorphic phantom identified the optimal airgap technique. In phase 2, lateral projections of the lumbar spine were performed on 50 patients randomly assigned equally into a control group (using the antiscatter grid) and an experimental group (using the airgap technique). The dose area product (DAP) was recorded, keeping other variables constant. Image quality evaluation was performed by 5 radiologists performing Absolute Visual Grading Analysis (VGA) using an image quality score tool, with resultant scores analysed using Visual Grading Characteristics (VGC). ResultsA 10 cm airgap in conjunction with a source to image distance (SID) of 121 cm was found as the optimal airgap technique. The clinical application of this technique resulted in a statistically significant (p < 0.05) reduction in DAP of 72%. Image quality scores were higher for the antiscatter grid but variation between the two techniques was not significant (p > 0.05). ConclusionReplacing the antiscatter grid with an airgap technique in lateral lumbar spine digital radiography, provides a significant dose reduction whilst still maintaining diagnostic image quality. Implications for practiceThe airgap technique is a simple and easy technique to implement and radiographers should find no difficulties in applying it, as It involves no additional cost and no additional equipment.

Estimating radiation exposure during paediatric cardiac catheterisation: a potential for radiation reduction with air gap technique.

The air gap technique (AGT) is an approach to radiation dose optimisation during fluoroscopy where an "air gap" is used in place of an anti-scatter grid to reduce scatter irradiation. The AGT is effective in adults but remains largely untested in children. Effects are expected to vary depending on patient size and the amount of scatter irradiation produced. Fluoroscopy and cineangiography were performed using a Phillips Allura Fluoroscope on tissue simulation anthropomorphic phantoms representing a neonate, 5-year-old, and teenager. Monte Carlo simulations were then used to estimate effective radiation dose first using a standard recommended imaging approach and then repeated using the AGT. Objective image quality assessments were performed using an image quality phantom. Effective radiation doses for the neonate and 5-year-old phantom increased consistently (2-92%) when the AGT was used compared to the standard recommended imaging approaches in which the anti-scatter grid is removed at baseline. In the teenage phantom, the AGT reduced effective doses by 5-59%, with greater dose reductions for imaging across the greater thoracic dimension of lateral projection. The AGT increased geometric magnification but with no detectable change in image blur or contrast differentiation. The AGT is an effective approach for dose reduction in larger patients, particularly for lateral imaging. Compared to the current dose optimisation guidelines, the technique may be harmful in smaller children where scatter irradiation is minimal.

Transient and steady‐state modelling of healthy and eccentric induction motors considering the main and third harmonic saturation factors

This paper deals with the modelling of magnetic saturation in induction motors (IMs) with particular focus on the equivalent or fictitious air-gap permeance technique. Besides, an improved version of this technique is provided so as to account for the transient starting process and the third harmonic saturation factor in addition to the fundamental one. This is for the symmetric case. Under air-gap eccentricities, extension of both saturation models is proposed using the varying saturation factor solution. The 2D-modified winding function approach (2D-MWFA) is the base of the inductance calculation and the state equations are derived from the well-known multiple coupled circuit model (MCCM). Thanks to such considerations, skew effect, rise of the magneto-motive force (MMF) across the slots, all winding harmonics, and many faulty states can be judiciously taken into account. In summary, five derived saturation models are discussed in favour of a good handling of the saturation phenomenon in cage IMs. The work is supported by extensive simulation and experimental results of eccentricity, broken rotor bar, and combined faults.

Design of dual-band microstrip patch antenna with right-angle triangular aperture slot for energy transfer application

This work focusing on the dual-band antenna design with rectifying circuit for energy transfer system technology for enhancement gain performance. The air gap technique is applied on this microstrip antenna design work to enhance the antenna gain. The work begins with designing and analyzing the antenna via the CST Microwave Studio software. After validation on acceptable performance in simulation side is obtained, the return loss, S11 of the antenna is measured using vector network analyzer equipment. The rectifier circuit is used to convert the captured signal to DC voltage. This projected dual-band antenna has successfully accomplished the target on return loss of −44.707 dB and −32.163 dB at dual resonant frequencies for 1.8 GHz and 2.4 GHz, respectively. This proposed antenna design benefits in low cost fabrication and has achieved high gain of 6.31 dBi and 7.82 dBi for dual-band functioning frequencies.

Study, Simulation and Optimization of an 8×1 Array Antenna for Electronic Scanning Radar Application

The need of detecting targets in different positions has become very important. Nowadays, the electronic scanning radars ensure this functionality by using electronic devices instead of mechanical ones. The major key of this type of radars is the antenna array which is the subject of this paper. The conception details are given for both the single radiating element and the 8-element linear antenna array operating at 3 GHz frequency. The structure is printed on a FR-4 substrate with a dielectric constant of =4.3. After analyzing the simulation results, authors deduced a low performance of the antenna array because of some limitations which are detailed in this paper. Hence, the design of the array antenna is optimized using the air gap technique between the FR-4 layer and the ground plane giving thereby good results and efficiency at the operating frequency. Both the designs and the simulations of this study are performed under the Advanced Design System (ADS) tool. The simulated results include the VSWR, the return loss, the gain and the directivity.

Improvement of radiographic visibility using an image restoration method based on a simple radiographic scattering model for x-ray nondestructive testing

In conventional radiography, image visibility is often limited mainly due to the superimposition of the object’s structure under investigation and scattered x-rays. Several methods, including the antiscatter grid technique, the air-gap technique, and scatter correction methods using measurements, mathematical-physical modeling, or a combination of both, have been extensively investigated in an attempt to overcome these difficulties. However, these methods require special equipment, geometry, and extra work to measure the scatter characteristics. In this study, we propose a new image restoration method based on a simple radiographic scattering model in which the intensity of the scattered x-rays and the direct transmission function of a given object are estimated from a single x-ray image by using the dark-channel prior. We implemented the proposed algorithm and performed a systematic experiment by using a 450-kV industrial x-ray inspection system to demonstrate its viability for nondestructive testing. Our results indicated that the structure of the examined object was much more clearly visible in the restored image, considerably improving the radiographic visibility.

Mammography image restoration based on a radiographic scattering model from a single projection: Experimental study

In conventional mammography, contrast sensitivity remains limited due to the superimposition of breast tissue and scattered X-rays, which induces low visibility of lesions in the breast and, thus, an excessive number of false-positive findings. Several methods, including digital breast tomosynthesis as a multiplanar imaging modality, air-gap and slot techniques for the reduction of scatters, phase-contrast imaging as another image-contrast modality, etc., have been investigated in attempt to overcome these difficulties. However, those techniques typically require a higher imaging dose or special equipment. In this work, as an alternative, we propose a new image restoration method based on a radiographic scattering model in which the intensity of scattered X-rays and the direct transmission function of a given medium are estimated from a single projection by using the dark-channel prior. We implemented the proposed algorithm and performed an experiment to demonstrate its viability. Our results indicate that most of the structures in the examined breast were very discernable even with no adjustment in the display-window level, thus preserving superior image features and edge sharpening.

EFFECT OF AIR-GAP TECHNIQUE IN BANDWIDTH OF MICROSTRIP PATCH ARRAY ANTENNA

Study of sixteen elements microstrip array antenna of rectangular patches which is printed on the RT-duroid substrate, is presented in this paper. Air- Gap technique is used in this array configuration for the enhancement of Bandwidth. To study the bandwidth enhancement the radiation patterns have been plotted for E-plane, H-plane and array geometry. A precise comparison of radiation parameters of this array antenna are also performed with the same array antenna configuration without using Air-Gap technique. This Air-Gap bandwidth enhancement technique has provided around 62% enhancement. This technique is quite easy in implementation and make antenna structure very light weighted and handy essential for portable devices.

Radiation dosage during pediatric diagnostic or interventional cardiac catheterizations using the "air gap technique" and an aggressive "as low as reasonably achievable" radiation reduction protocol in patients weighing

Background:Cardiac catheterizations expose both the patient and staff to the risks of ionizing radiation. Studies using the “air gap” technique (AGT) in various radiological procedures indicate that its use leads to reduction in radiation exposure but there are no data on its use for pediatric cardiac catheterization. The aim of this study was to retrospectively review the radiation exposure data for children weighing <20 kg during cardiac catheterizations using AGT and an “as low as reasonably achievable (ALARA)” radiation reduction protocol.Patients and Methods:All patients weighing <20 kg who underwent cardiac catheterization at the Children's Hospital at Montefiore (CHAM), New York, the United States from 05/2011 to 10/2013 were included. Transplant patients who underwent routine endomyocardial biopsy and those who had surgical procedures at the time of the catheterizations were excluded. The ALARA protocol was used in concert with AGT with the flat panel detector positioned 110 cm from the patient. Demographics, procedural data, and patient radiation exposure levels were collected and analyzed.Results:One-hundred and twenty-seven patients underwent 151 procedures within the study period. The median age was 1.2 years (range: 1 day to 7.9 years) and median weight was 8.8 kg (range: 1.9-19.7). Eighty-nine (59%) of the procedures were interventional. The median total fluoro time was 13 min [interquartile range (IQR) 7.3-21.8]. The median total air Kerma (K) product was 55.6 mGy (IQR 17.6-94.2) and dose area product (DAP) was 189 Gym2 (IQR 62.6-425.5).Conclusion:Use of a novel ALARA and AGT protocol for cardiac catheterizations in children markedly reduced radiation exposure to levels far below recently reported values.Abbreviations: AGT: Air gap technique, ALARA: As low as reasonably achievable.

Radiation Reduction Capabilities of a Next-Generation Pediatric Imaging Platform.

The aims of this study were to quantify patient radiation exposure for a single interventional procedure during transition from an adult catheterization laboratory to a next-generation imaging system with pediatric settings, and to compare this radiation data to published benchmarks. Radiation exposure occurs with any X-ray-directed pediatric catheterization. Technologies and imaging techniques that limit dose while preserving image quality benefit patient care. Patient radiation dose metrics, air kerma, and dose-area product (DAP) were retrospectively obtained for patients <20 kg who underwent patent ductus arteriosus (PDA) closure on a standard imaging system (Group 1, n = 11) and a next-generation pediatric imaging system (Group 2, n = 10) with air-gap technique. Group 2 radiation dose metrics were then compared to published benchmarks. Patient demographics, procedural technique, PDA dimensions, closure devices, and fluoroscopy time were similar for the two groups. Air kerma and DAP decreased by 65-70% in Group 2 (p values <0.001). The average number of angiograms approached statistical significance (p value = 0.06); therefore, analysis of covariance (ANCOVA) was conducted that confirmed significantly lower dose measures in Group 2. This degree of dose reduction was similar when Group 2 data (Kerma 28 mGy, DAP 199 µGy m(2)) was compared to published benchmarks for PDA closure (Kerma 76 mGy, DAP 500 µGy m(2)). This is the first clinical study documenting the radiation reduction capabilities of a next-generation pediatric imaging platform. The true benefit of this dose reduction will be seen in patients requiring complex and often recurrent catheterizations.

A novel wide band open ended air gap radial line slot array antenna at 5.8-GHz frequency band

This article presents a wide band linearly polarized beam squinted radial line slot array (RLSA) antenna at 5.8-GHz band. The open ended air gap technique was used to broader the bandwidth, reduce the antenna size but maintain the high-performance characteristic. The antenna implemented radiating slot design with diameter of 200 and 1.6 mm hybrid FR4 and 8-mm open ended air gap for dielectric height. The antenna also successfully fabricated and performed a good result. The measured results show a wide 38% of bandwidth with 16 dBi gain at 5.8-GHz frequency. The beamwidth obtained below 15° for E and H plane. The research found a wide band RLSA antenna can be achieved using air gap technique and will be a potential candidate for future point to point application for fixed broadband wireless access. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:938–944, 2014

Design of UHF radio frequency identification metal tag antenna using T-shaped slot

In this article, we have proposed a novel ultra high frequency (UHF) radio frequency identification (RFID) metal tag antenna mountable on the metallic surface. Three techniques (T-shaped slot, two rectangular slots for impedance matching, and air gap technique for reading distance enhancement) are used to obtain a good performance of metal tag antenna on the metallic surface. All simulations are carried out by Ansoft HFSS software. Moreover, by fabricating the antenna, the simulation results are verified by experimental data. Good performances such as reading distance and sensitivity have been observed. Details of the proposed antenna design and the simulated and measured results are presented and discussed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2251–2255, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26297

Optimisation of computed radiography systems for chest imaging

The main thrust of this study is to investigate methods of optimising the radiation dose–image quality relationship in computed radiography (CR) systems for chest imaging. Specifically, this study investigates the possibility of reducing the patient radiation exposure through an optimal selection of tube filtration, exposure parameters and air gap technique, in parallel with a study of the image quality, particularly low contrast detail detectability, signal-to-noise ratio (SNR) and scatter fraction (SF). The CDRAD phantom was used to assess the quality of the CR images. Tissue equivalent Polystyrene blocks were placed in the front of the phantom as scattering material with thicknesses of 5 and 15 cm to simulate an adult chest and heart/diaphragm regions, respectively. A series of exposure techniques were used, including Cu filtration with various thicknesses of Cu in the presence and absence of an air gap, whilst the exposure was kept as constant as possible throughout. The estimated patient effective dose and skin entrance dose were calculated using the NRPB-SR262 X-ray dose calculation software. The results have shown that the low contrast-detail detectability in the lung and the heart/diaphragm regions improves when using an air gap and no Cu filtration, particularly at low kilovoltage (kVp). However, there is no significant difference in low contrast-detail in the absence or presence of a 0.2 mm Cu filtration. SF values for the lung and heart regions decrease when using both, the air gap technique and a 0.2 mm Cu filtration, particularly at low kVp. SNR values for the lung and heart regions improve when using a small Cu thickness. In conclusion, this investigation has shown that the quality of chest CR images could be improved by using an air gap technique and a 0.2 mm Cu filtration at low kVp, particularly at 99 kVp.