Tube Loading Research Articles

Influence of Rotating Band Construction on Gun Tube Loading—Part I: Numerical Approach

The effects of changes in geometries and material properties of rotating band and long range artillery projectile shell body on gun tube stress are presented. The results are based on numerical calculations (finite element analysis, FEA). Numerical explicit dynamic analyses were performed assuming elastic–plastic material behavior and nonlinear kinematics. Mechanical loading of shell body was controlled by pressure–time relationship based on the simulation of internal ballistic cycle. One degree slice of projectile and forcing cone section of gun tube was modeled as simplified smooth bore 3D analysis model. The results were in agreement with the measured results in firing trials and also with the results presented in open literature. Although simplified computations were used, the influences of the structural modifications of the rotating band and the shell body were shown.

Influence of Rotating Band Construction on Gun Tube Loading—Part II: Measurement and Analysis

The soft deformable metallic rotating band of large caliber projectiles prevents the gas leakage between the gun tube wall and the shell body by the band pressure on contact surfaces during the launch cycle of the gun. High rotating band pressures can lead to problems concerning gun tube wear, fatigue, and strength. The effects of changes in construction of rotating band and long range artillery projectile shell body on gun tube loading are studied experimentally. A practical analysis method for tube inner wall pressure computation from outer wall strain measurements is presented. The method is based on assuming stepped pressure load affecting on tube inner wall surface, when the projectile passes the measurement point. Although the analysis method was simplified, it was found to give useful and reliable results for comparative verification of different shell and band structures and their influences on gun tube loading. The structural design of the shell body and the rotating band were shown to be the most important aspects to cause the extreme loadings on the gun tube.

TU-E-217BCD-01: X-Ray Spectra for Breast CT.

To study a range of x-ray spectra with regard to their suitability for dedicated breast CT, taking into account realistic tube loading limitations. A simple theoretical model was used to get a preliminary indication of the best mono-energetic x-ray energy as a function of object size. That model was extended to poly-energetic spectra and used to study a range of object sizes, tube voltages, filter materials, and filter thicknesses. Spectra from IPEM Report 78 were used as input to the model. Initially we have looked at lanthanide filters (Z = 57-60) and tube voltages from 30 to 80 kVp. Outputs from the model included contrast, contrast-to-noise ratio (CNR), dose, dose efficiency (CNR̂2/dose), and tube loading. Dose was estimated as incident minus transmitted energy fluence. We have also started experiments to verify the computational results. Experiments are done using a bench-top cone beam CT and a 14 cm diameter cylindrical PMMA phantom filled with liquid mixtures equivalent to breast tissue of varying glandularity. We use reconstructed data to determine the CNR of a test block representing 100% glandular breast tissue, immersed in the liquid. Air kerma measurements are obtained at the center and periphery of the phantom, and used in the calculation of dose efficiency. Monte Carlo calculations are being done to get a more accurate dose estimate. For a constant CNR, computational results indicate that as filter thickness increases above 0.4 mm dose efficiency plateaus. However, the power required to maintain a constant CNR becomes prohibitively large for filter thicknesses greater than 0.3 mm. Spectra generated at tube voltages above 40 kVp are likely to provide the best trade-off between dose efficiency and tube loading. For lanthanide filters, there is little benefit from using thicknesses greater than 0.3 mm.

TU-E-BRA-08: A Comprehensive Study on the Relationship between Image Quality and Imaging Dose in Low-Dose Cone Beam CT.

To investigate image quality as a function of number of projections and tube load per projection in compressive sensing (CS) based low-dose cone beam CT (CBCT), and achieve optimal low-dose scan protocols in image guided radiation therapy (IGRT). We have performed CS-based CBCT reconstruction with different combinations of number of projections (from 46 to 364) and mAs (from 0.2 to 2.4 mAs/view), which covers the whole clinically relevant range. Image quality is assessed in each case. On this basis, optimal scan protocols are analyzed according to various IGRT applications. Image quality degrades ∼10% when the imaging dose decreases from 400 to 100 total mAs, further ∼10% from 100 to 40 total mAs, and another ∼80% below 40 total mAs. Image quality on iso-low-dose lines at 36.8, 72.6, 109.2 and 145.6 total mAs varies 17.16%, 13.69%, 11.99% and 5.74% in terms RMSE with various scanning protocols. 1) In CS-based CBCT, image quality has little degradation with imaging dose> 100 total mAs. Optimal low-dose scan protocols likely fall in the range of 40-100 total mAs. 2) At a constant low-dose level, the scan protocol that with super sparse views (projection number < 50) is the most challenging case. 3) The optimal scan protocol is the combination of a medium number of projections and a medium level of mAs/view. This is more evident when the dose is ∼72.8 total mAs or below, and when the ROI is a low-contrast or high-resolution object. 4) The clinically acceptable lowest imaging dose level is task dependent. In our study, 72.8mAs is a safe dose level for visualizing low-contrast objects, while 12.2 total mAs is sufficient for detecting high-contrast objects of diameter greater than 3 mm. This work is supported in part by NIH (1R01CA154747-01), Varian Medical Systems through a Master Research Agreement, and the Thrasher Research Fund.

OPTIMIZATION OF CONTRAST‐ENHANCED MULTIDETECTOR ABDOMINAL COMPUTED TOMOGRAPHY IN SEDATED CANINE PATIENTS

A major disadvantage of computed tomography for abdominal screening in dogs has been the need for general anesthesia to prevent motion artifacts. With multidetector helical CT, it is possible to decrease examination time, allowing patients to be scanned under sedation. It is also desirable to decrease tube loading to prolong x-ray tube life. To develop a protocol that will allow for examination of sedated patients with minimal image artifacts, milliamperage (mA) and helical pitch were varied, providing 16 experimental scan protocols. A standard clinical protocol was also tested, providing 17 protocols for evaluation. These protocols were tested, using a standard CT phantom, canine tissues in a water bath, and a canine cadaver. The cadaver images were scored semiquantitatively by three reviewers to determine the protocol with the best combination of speed and minimal image artifact. The optimized protocol was then applied to 27 sedated canine patients of three body weight categories. The images obtained were compared to the standard protocol by two reviewers for presence of motion, streak, and quantum mottle artifacts. There was significantly more streak artifact noted by one observer using the optimized study protocol, but no significant difference in any other category. Scanning under sedation was well tolerated in all patients, and sedated CT examination is a promising tool for screening abdominal disease in dogs.

Torsional stability of carbon nanotubes filled with copper atoms

Carbon nanotubes (CNTs) are frequently used as torsional devices in nanoelectromechanical systems; thus it is necessary to gain a thorough understanding of the mechanical behavior of tubes under torsion. In this paper, molecular dynamics simulations are carried out to investigate the torsional buckling of single-walled CNTs completely filled with copper atoms. Results show that, due to metal filling, the torsional rigidity of tubes can be dramatically enhanced and the critical torsional angles of filled tubes can be 2–4 times as high as those of empty ones. Furthermore, due to structural asymmetry in chiral metal-filled tubes, there exists a dependence of the torsional behavior on loading directions. The torsional response of metal-filled tubes is dependent on both tube chirality and loading direction. The microstructure of metal atoms may have a strong influence on the mechanical deformation of metal-filled tubes. These results can provide useful guidelines on the application of CNTs as torsional devices, especially in the case where high torsional stability is required.

A comprehensive study on the relationship between the image quality and imaging dose in low-dose cone beam CT

While compressed sensing (CS)-based algorithms have been developed for the low-dose cone beam CT (CBCT) reconstruction, a clear understanding of the relationship between the image quality and imaging dose at low-dose levels is needed. In this paper, we qualitatively investigate this subject in a comprehensive manner with extensive experimental and simulation studies. The basic idea is to plot both the image quality and imaging dose together as functions of the number of projections and mAs per projection over the whole clinically relevant range. On this basis, a clear understanding of the tradeoff between the image quality and imaging dose can be achieved and optimal low-dose CBCT scan protocols can be developed to maximize the dose reduction while minimizing the image quality loss for various imaging tasks in image-guided radiation therapy (IGRT). Main findings of this work include (1) under the CS-based reconstruction framework, image quality has little degradation over a large range of dose variation. Image quality degradation becomes evident when the imaging dose (approximated with the x-ray tube load) is decreased below 100 total mAs. An imaging dose lower than 40 total mAs leads to a dramatic image degradation, and thus should be used cautiously. Optimal low-dose CBCT scan protocols likely fall in the dose range of 40–100 total mAs, depending on the specific IGRT applications. (2) Among different scan protocols at a constant low-dose level, the super sparse-view reconstruction with the projection number less than 50 is the most challenging case, even with strong regularization. Better image quality can be acquired with low mAs protocols. (3) The optimal scan protocol is the combination of a medium number of projections and a medium level of mAs/view. This is more evident when the dose is around 72.8 total mAs or below and when the ROI is a low-contrast or high-resolution object. Based on our results, the optimal number of projections is around 90 to 120. (4) The clinically acceptable lowest imaging dose level is task dependent. In our study, 72.8 mAs is a safe dose level for visualizing low-contrast objects, while 12.2 total mAs is sufficient for detecting high-contrast objects of diameter greater than 3 mm.

Solar Energy, the Heat Collector Device Research and Application

A curved glass evacuated solar collector tube welding and metal melting point, to achieve the stability of vacuum time. Application of the solar collector tube, the heat collector device, solar radiation intensity in 17MJ/M2 cases, after 30 minutes of sunshine arc temperature of solar vacuum tube load up to 480 °C or above, add heat transfer medium after the medium output temperatures up to 220 °C. Solar vacuum tube with curved endothermic components help focus line fluctuations, solar energy in order to achieve high-temperature heating, the high temperature heat output.

How Much Dose Can Be Saved in Three-Phase CT Urography? A Combination of Normal-Dose Corticomedullary Phase With Low-Dose Unenhanced and Excretory Phases

The purpose of this study was to investigate the degree to which the total radiation dose for CT urography can be lowered by selective reduction of the dose in the unenhanced and excretory phases when images in these phases are systematically evaluated alongside normal-dose corticomedullary phase images. Twenty-seven patients (mean age, 74±9 years) underwent single-bolus CT urography with acquisition in the unenhanced, corticomedullary, and 5-minute excretory phases. The scanning parameters for normal-dose CT urography were as follows: 16×0.75 mm, 120 kV, and automatic exposure control technique reference tube loads of 100, 120, and 100 effective mAs (mAseff). The patients also underwent low-dose unenhanced and excretory phase scanning, in which the dose was escalated stepwise from a volume CT dose index (CTDIvol) of 1.7 to 6.6 mGy (reference 20-40-60-80 mAseff). Images were analyzed for quality and diagnostic confidence. If low-dose scans of three patients were inadequate, the study continued to the next dose level. When 20 patients were successfully included in the unenhanced and excretory phase groups, the study ended. Doses were calculated with a CT patient dosimetry calculator. Combined with the normal dose for corticomedullary phase scanning, doses of CTDIvol 1.5 mGy for the unenhanced phase and CTDIvol 2.7 mGy for the excretory phase were sufficient. The effective dose for three-phase CT urography was lowered from 16.2 to 9.4 mSv, a decrease of 42%. Diagnostic confidence in low-dose images was equal to that in normal-dose images when low-dose unenhanced and excretory phase images were read along-side normal-dose corticomedullary phase images. With a three-phase CT urographic protocol, significant dose reductions in the unenhanced and excretory phases can be achieved when these phases are combined with a normal-dose corticomedullary phase.

Determination of equivalent breast phantoms for different age groups of Taiwanese women: An experimental approach

Polymethylmethacrylate (PMMA) slab is one of the mostly used phantoms for studying breast dosimetry in mammography. The purpose of this study was to evaluate the equivalence between exposure factors acquired from PMMA slabs and patient cases of different age groups of Taiwanese women in mammography. This study included 3910 craniocaudal screen/film mammograms on Taiwanese women acquired on one mammographic unit. The tube loading, compressed breast thickness (CBT), compression force, tube voltage, and target/filter combination for each mammogram were collected for all patients. The glandularity and the equivalent thickness of PMMA were determined for each breast using the exposure factors of the breast in combination with experimental measurements from breast-tissue-equivalent attenuation slabs. Equivalent thicknesses of PMMA to the breasts of Taiwanese women were then estimated. The average +/- standard deviation CBT and breast glandularity in this study were 4.2 +/- 1.0 cm and 54% +/- 23%, respectively. The average equivalent PMMA thickness was 4.0 +/- 0.7 cm. PMMA slabs producing equivalent exposure factors as in the breasts of Taiwanese women were determined for the age groups 30-49 yr and 50-69 yr. For the 4-cm PMMA slab, the CBT and glandularity values of the equivalent breast were 4.1 cm and 65%, respectively, for the age group 30-49 yr and 4.4 cm and 44%, respectively, for the age group 50-69 yr. The average thickness of PMMA slabs producing the same exposure factors as observed in a large group of Taiwanese women is less than that reported for American women. The results from this study can provide useful information for determining a suitable thickness of PMMA for mammographic dose survey in Taiwan. The equivalence of PMMA slabs and the breasts of Taiwanese women is provided to allow average glandular dose assessment in clinical practice.

TU‐G‐110‐08: Feasibility of Tissue Composition Measurement with Dual Energy Computed Tomography

Purpose: To investigate the feasibility of tissue composition measurement with dual energy computed tomography as compositional information may help to better characterize suspicious lesions. Method and Materials: Simulations and experimental studies were performed for a flat panel dual energy dual kVp CT system. Simulations were performed to identify optimal beam energy combinations. A figure of merit (FOM) was used to determine the optimal dual energy signal to noise ratio with respect to mean glandular dose. Beam energies ranging from 40 to 140 kVp were simulated in 1 kVp increments. The distribution of dose between low and high energy images was simulated at intervals of 10%. An experimental calibration phantom of 3.175 cm in diameter was constructed from a polyoxymethylene plastic with cylindrical holes filled with water and oil. Similar size samples of pure adipose and lean bovine tissues were also prepared. The phantom and tissue samples were imaged with the dual energy CT system. The calibration phantom was used to estimate the water, lipid and protein contents of each tissue sample. Tissue composition results computed from images were compared to data from chemical analysis of prior tissue samples. Results: The predicted spectra from simulation which optimized the FOM were at beam energies of 40 kVp and 140 kVp with the mean glandular dose divided equally between each exposure. Given tube loading and system constraints, experimental beam energies for the dual kVp CT system were selected to be 50 kVp and 120 kVp. The percentage RMS errors of water, lipid and protein contents as compared to data from chemical analysis were 10.9% for the dual kVp technique. Conclusion: The results of this study suggest that the water, lipid, and protein content may be measured with dual energy CT with relatively good agreement. This might potentially be useful for characterizing suspicious lesions.

TU‐C‐211‐03: Increasing X‐Ray Tube Output for Small Focal Spot, Region‐Of‐Interest Imaging

Purpose: High‐resolution region‐of‐interest (ROI) imaging requires the use of a small focal spot with sufficient output to maintain spatial and contrast resolution. We investigate methods to increase the x‐ray output while maintaining the focal‐spot size for a small field‐of‐view (FOV) as needed for endovascular‐image‐guided interventions (EIGIs).Materials and Methods: We evaluated the increase in tube output made possible by reducing the anode angle and lengthening the filament for the small focal spot to maintain a constant effective focal‐spot size. Since the area of heat deposition on the anode is increased, tube‐loading capacity increases and the mA can be increased proportionally if the electron flux density at the target is unchanged. “Spek Calc” software was used to calculate the change in inherent tube filtration and in x‐ray spectrum and intensity as a function of anode angle. The gain in tube output achievable while maintaining focal‐spot size was determined for the small‐FOV of our custom high‐resolution, ROI imager. When the same tube is used for both large‐FOV imager and the small‐FOV ROI imager, angling the tube and adjusting filament length can allow a tradeoff between spatial resolution, tube loading and FOV. Results: For the 5‐cm FOV needed in neurovascular ROI imaging, the x‐ray output could be increased substantially with decreasing anode angle while the focal‐spot size and FOV is maintained. Considering both increased anode‐target area and increased inherent anode filtration, a net output increase of 3.3 times could be achieved with a 2‐ degree anode angle compared to the standard 8‐degree target with an increase of 4 times in filament length. Conclusions: For EIGIs where high resolution is essential but only over a small FOV, higher tube output while maintaining a small focal spot should be achievable with only small modification of standard x‐ray tube geometry.Support: NIH Grants R01‐EB008425, R01‐EB002873

Optimized low-kV spectrum of dual-energy CT equipped with high-kV tin filtration for electron density measurements

This paper describes the low-kV spectral optimization of dual-energy CT (DECT) equipped with high-kV tin filtration for the quantitative acquisition of electron density information, which is essential for treatment planning in radiotherapy. In addition, an analytical DECT image simulation was preliminarily performed to demonstrate the effectiveness of the optimized DECT with respect to the beam-hardening reduction. To optimize the low-kV spectrum of DECT, the author calculated the beam-hardening error, CT dose index, and tube loadings for a 50-cm diameter cylindrical water phantom with various combinations of filter materials, a range of thicknesses, and low-kV tube potentials. In addition, a single tube potential of 140 kV filtered by 0.4 mm tin (Sn) was employed for high-kV scanning, as is similar to the commercial implementation of the second-generation dual-source CT scanner. The optimized spectral parameters were then applied to the analytical DECT image simulation using two-dimensional fan-beam geometry for a virtual solid water phantom with 16 bodylike tissue inserts. The author predicts that an optimal low-kV filtration would be 0.144-mm tungsten (W) at 90 kV, as it yields a minimal beam-hardening error with lower tube loadings and dose. The high-kV tube loading and dose obtained using the W filtration were 99 mAs and 2.2 mGy, respectively. These values are nearly equal to those obtained in the case of 2.5 mm Al at 100 kV (100 mAs and 2.3 mGy), which was regarded in this study as a reference filtration; however, the W filtration significantly reduced the beam-hardening error, from 9.5 to 1.4%. The corresponding low-kV tube loading (112 mAs) was five times greater than that of the reference case (21 mAs), but it was maintained at a certain practical level since the low-kV tube loading was comparable to the high-kV tube loading of the reference (100 mAs). The superiority of the beam-hardening reduction is reflected in the simulated images; for example, by the use of the W filter, the beam-hardening-induced deviation between the simulated and theoretical electron density values of cortical bone was reduced from 7.4 to 1.2% as compared with the reference filtration, even though no correction for beam hardening was performed. In terms of beam hardening reduction, the DECT with the low-kV W filtration is more effective for the quantitative measurement of electron density within a practical limit of tube loadings and without additional dose.

Method for measuring the focal spot size of an x‐ray tube using a coded aperture mask and a digital detector

The goal of this study is to evaluate a new method based on a coded aperture mask combined with a digital x-ray imaging detector for measurements of the focal spot sizes of diagnostic x-ray tubes. Common techniques for focal spot size measurements employ a pinhole camera, a slit camera, or a star resolution pattern. The coded aperture mask is a radiation collimator consisting of a large number of apertures disposed on a predetermined grid in an array, through which the radiation source is imaged onto a digital x-ray detector. The method of the coded mask camera allows one to obtain a one-shot accurate and direct measurement of the two dimensions of the focal spot (like that for a pinhole camera) but at a low tube loading (like that for a slit camera). A large number of small apertures in the coded mask operate as a "multipinhole" with greater efficiency than a single pinhole, but keeping the resolution of a single pinhole. X-ray images result from the multiplexed output on the detector image plane of such a multiple aperture array, and the image of the source is digitally reconstructed with a deconvolution algorithm. Images of the focal spot of a laboratory x-ray tube (W anode: 35-80 kVp; focal spot size of 0.04 mm) were acquired at different geometrical magnifications with two different types of digital detector (a photon counting hybrid silicon pixel detector with 0.055 mm pitch and a flat panel CMOS digital detector with 0.05 mm pitch) using a high resolution coded mask (type no-two-holes-touching modified uniformly redundant array) with 480 0.07 mm apertures, designed for imaging at energies below 35 keV. Measurements with a slit camera were performed for comparison. A test with a pinhole camera and with the coded mask on a computed radiography mammography unit with 0.3 mm focal spot was also carried out. The full width at half maximum focal spot sizes were obtained from the line profiles of the decoded images, showing a focal spot of 0.120 mm x 0.105 mm at 35 kVp and M = 6.1, with a detector entrance exposure as low as 1.82 mR (0.125 mA s tube load). The slit camera indicated a focal spot of 0.112 mm x 0.104 mm at 35 kVp and M = 3.15, with an exposure at the detector of 72 mR. Focal spot measurements with the coded mask could be performed up to 80 kVp. Tolerance to angular misalignment with the reference beam up to 7 degrees in in-plane rotations and 1 degrees deg in out-of-plane rotations was observed. The axial distance of the focal spot from the coded mask could also be determined. It is possible to determine the beam intensity via measurement of the intensity of the decoded image of the focal spot and via a calibration procedure. Coded aperture masks coupled to a digital area detector produce precise determinations of the focal spot of an x-ray tube with reduced tube loading and measurement time, coupled to a large tolerance in the alignment of the mask.

Analysis of patient dose in full field digital mammography

Now, full field digital mammography (FFDM) is widely used in diagnosis of breast cancer. With the development of FFDM, the radiation dose delivered to the patients involved in an imaging protocol is of utmost concern. Here, we analyzed the average glandular dose (AGD) and entrance surface exposure (ESE) of 1397 patients (6008 images) who underwent mammographic examinations by FFDM in three modes with automatic optimization of parameters (AOP), namely STD for standard mode, CNT for contrast mode and DOSE for dose mode. In addition, exposure factors including kVp, tube loading (mAs), and target/filter combination were evaluated. As a result, the patient dose was sorted as CNT>STD>DOSE. The dose difference among the three AOP modes was mainly attributed to the selection of mAs. The AGD and breast compressed thickness were well correlated in STD and DOSE modes. However, the correlation between CNT-delivered AGD and breast compressed thickness was dependent on the range of the breast thickness and patient age. The findings on dose and exposure characteristics of the three AOP modes get useful message of patient dose in the acquisition of FFDM.

BEHAVIOR CHARACTERISTICS OF BUCKLING-RESTRAINED BRACES USING ROUND STEEL BAR CORES AND DOUBLE STEEL TUBES

In the previous research by the authors, the buckling restrained braces (BRBs) using round steel bar cores and double steel tubes were developed and some loading tests revealed that the BRBs have sufficient capability as hysteretic dampers. However the test specimens were relatively small and limited to the rigid connection type. The present paper firstly presents evaluation of the rotation characteristics of the outer tube end and loading tests using the element specimens. Then some full-scale tests are conducted using rather large test specimens in which the pin connection type BRBs are employed in addition to the rigid connection type ones. The test results reveal the behavior of the inner tubes, influence of the number of contraction allowance parts, energy dissipation capacity and behavior characteristics of the pin connection type BRBs. Finally, the design conditions of the outer tubes are discussed considering the evaluation results of the rotation characteristics of the outer tube end.

スリット撮影を用いた長尺撮影装置における全脊椎撮影の最適化

The purpose of this study was to optimize X-ray conditions for full spine X-ray examinations in slot-scan digital radiography (SSDR). Follow-up of spinal deformities, such as scoliosis, typically involves many radiographs of the patient throughout childhood and adolescence. The Radiation doses for the full spine X-ray examination should be minimized. Recently, SSDR has been introduced for full spine as well as lower extremity examinations. This system utilizes slot scanning geometry to acquire the radiographic images. X-ray energy characteristics of direct amorphous Selenium (a-Se) digital fluoroscopy and short time X-ray tube loads of this system were investigated. Orthopedists evaluated the irradiation time for full spine radiographs in various conditions using an observer study. Patient doses were measured with radiophotoluminescence glass dosimeters, which were implanted in various tissue and organ positions within an anthropomorphic phantom. In the optimization of conditions for SSDR, patient doses are reduced by approximately 60% compared to default setting.

A method for calculating the dose length product from CT DICOM images

The dosimetric calculations in CT examinations are currently based on two quantities: the volume weighted CT dose index (CTDI(vol)) and the dose-length product (DLP). The first quantity is dependent on the exposure factors, scan field of view, collimation and pitch factor selections, whereas the second is additionally dependent on the scan length. In this study a method for the calculation of these quantities from digital imaging and communication in medicine (DICOM) CT images is presented that allows an objective audit of patient doses. This method was based on software that has been developed to enable the automatic extraction of the DICOM header information of each image (relating to the parameters that affect the aforementioned quantities) into a spreadsheet with embedded functions for calculating the contribution of each image to the CTDI(vol) and DLP values. The applicability and accuracy of this method was investigated using data from actual examinations carried out in three different multislice CT scanners. These examinations have been performed with the automatic exposure control systems activated, and therefore the tube current and tube loading values varied during the scans. The calculated DLP values were in good agreement (±5%) with the displayed values. The calculated average CDTI(vol) values were in similar agreement with the displayed CTDI(vol) values but only for two of the three scanners. In the other scanner the displayed CTDI(vol) values were found to be overestimated by about 25%. As an additional application of this method the differences among the tube modulation techniques used by the three CT scanners were investigated. This method is a useful tool for radiation dose surveys.

INVESTIGATION OF THE PRACTICAL ASPECTS OF AN ADDITIONAL 0.1 MM COPPER X-RAY SPECTRAL FILTER FOR CINE ACQUISITION MODE IMAGING IN A CLINICAL CARE SETTING

Minimizing the x-ray radiation dose is an important aspect of patient safety during interventional fluoroscopy procedures. This work investigates the practical aspects of an additional 0.1 mm Cu x-ray beam spectral filter applied to cine acquisition mode imaging on patient dose and image quality. Measurements were acquired using clinical interventional imaging systems. Acquisition images of Solid Water phantoms (15-40 cm) were acquired using x-ray beams with the x-ray tube inherent filtration and using an additional 0.1 mm Cu x-ray beam spectral filter. The skin entrance air kerma (dose) rate was measured and the signal difference to noise ratio (SDNR) of an iodine target embedded into the phantom was calculated to assess image quality. X-ray beam parameters were recorded and analyzed and a primary x-ray beam simulation was performed to assess additional x-ray tube burden attributable to the Cu filter. For all phantom thicknesses, the 0.1 mm Cu filter resulted in a 40% reduction in the entrance air kerma rate to the phantoms and a 9% reduction in the SDNR of the iodine phantom. The expected additional tube load required by the 0.1 mm Cu filter ranged from 11% for a 120 kVp x-ray beam to 43% for a 60 kVp beam. For these clinical systems, use of the 0.1 mm Cu filter resulted in a favorable compromise between reduced skin dose rate and image quality and increased x-ray tube burden.

Dose optimization in pediatric cardiac x‐ray imaging

The aim of this research was to explore x-ray beam parameters with intent to optimize pediatric x-ray settings in the cardiac catheterization laboratory. This study examined the effects of peak x-ray tube voltage (kVp) and of copper (Cu) x-ray beam filtration independently on the image quality to dose balance for pediatric patient sizes. The impact of antiscatter grid removal on the image quality to dose balance was also investigated. Image sequences of polymethyl methacrylate phantoms approximating chest sizes typical of pediatric patients were captured using a modern flat-panel receptor based x-ray imaging system. Tin was used to simulate iodine-based contrast medium used in clinical procedures. Measurements of tin detail contrast and flat field image noise provided the contrast to noise ratio. Entrance surface dose (ESD) and effective dose (E) measurements were obtained to calculate the figure of merit (FOM), CNR2/dose, which evaluated the dose efficiency of the x-ray parameters investigated. The kVp, tube current (mA), and pulse duration were set manually by overriding the system's automatic dose control mechanisms. Images were captured with 0, 0.1, 0.25, 0.4, and 0.9 mm added Cu filtration, for 50, 55, 60, 65, and 70 kVp with the antiscatter grid in place, and then with it removed. For a given phantom thickness, as the Cu filter thickness was increased, lower kVp was favored. Examining kVp alone, lower values were generally favored, more so for thinner phantoms. Considering ESD, the 8.5 cm phantom had the highest FOM at 50 kVp using 0.4 mm of Cu filtration. The 12 cm phantom had the highest FOM at 55 kVp using 0.9 mm Cu, and the 16 cm phantom had highest FOM at 55 kVp using 0.4 mm Cu. With regard to E, the 8.5 and 12 cm phantoms had the highest FOM at 50 kVp using 0.4 mm of Cu filtration, and the 16 cm phantom had the highest FOM at 50 kVp using 0.25 mm Cu. Antiscatter grid removal improved the FOM for a given set of x-ray conditions. Under aforesaid optimal settings, the 8.5 cm phantom FOM improved by 24% and 33% for ESD and E, respectively. Corresponding improvements were 26% and 24% for the 12 cm phantom and 6% and 15% for the 16 cm phantom. For pediatric patients, using 0.25-0.9 mm Cu filtration in the x-ray beam while maintaining 50-55 kVp, depending on patient size, provided optimal x-ray image quality to dose ratios. These settings, adjusted for x-ray tube loading limits and clinically acceptable image quality, should provide a useful strategy for optimizing iodine contrast agent based cardiac x-ray imaging. Removing the antiscatter grid improved the FOM for the 8.5 and 12 cm phantoms, therefore grid removal is recommended for younger children. Improvement for the 16 cm phantom declined into the estimated margin of error for the FOM; the need for grid removal for older children would depend on practical feasibility in the clinical environment.