Tungsten Anode Research Articles

Temperature Measurement of Tungsten Electrode Surface at Electric Arc Extinction in Air–Power Flux Estimation

This paper deals with temperature measurements of the surface of tungsten electrodes submitted to electric arcs in nonstationary regimes in air at atmospheric pressure and with the estimation of the power and power density brought by electric arcs to the electrodes. Temperature measurements are proposed for tungsten anodes and cathodes for current intensity of ~30 A and duration of 3 ms. The temperature of the electrode surface at the instant the arc extinguishes is estimated in both electrode polarities. These experimental results are used in a model to estimate the power and the power density brought to the tungsten electrode surface by electric arcs. We found that the power surface density brought by electric arcs to the electrodes was in the range 1. × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> -1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the case of anodes and in the range 1.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> -1.9×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the case of cathodes. It has also been found that reactions of tungsten oxidation had to be considered to explain the high values obtained for the power brought to the electrodes.

Effect of Rod Material on the Impedance Behavior of Small Aspect Ratio Rod Pinches

A series of experiments on small aspect ratio rod pinches using solid tungsten, solid graphite, and thin-wall tantalum anode rods driven by a nominally 375-kV linear transformer driver, powered inductive voltage adder has characterized the impedance behavior over a range of aspect ratios and materials. For the tungsten and tantalum anodes, the impedance behavior is well described by the pinched current for self-magnetically insulated flow in a cylindrical geometry with ions present and gap closure velocities of 1-2 cm/μs. The graphite anodes always exhibited strong localized pinching of the electron beam onto the anode rod, with substantially higher operating impedance, as well as a delay in the formation of the plasma at the anode. The graphite anodes also had a longer radiation delay time, consistent with the longer anode plasma formation time.

Analyzer-based phase-contrast imaging system using a micro focus X-ray source.

Here we describe a new in-laboratory analyzer based phase contrast-imaging (ABI) instrument using a conventional X-ray tube source (CXS) aimed at bio-medical imaging applications. Phase contrast-imaging allows visualization of soft tissue details usually obscured in conventional X-ray imaging. The ABI system design and major features are described in detail. The key advantage of the presented system, over the few existing CXS ABI systems, is that it does not require high precision components, i.e., CXS, X-ray detector, and electro-mechanical components. To overcome a main problem introduced by these components, identified as temperature stability, the system components are kept at a constant temperature inside of three enclosures, thus minimizing the electrical and mechanical thermal drifts. This is achieved by using thermoelectric (Peltier) cooling/heating modules that are easy to control precisely. For CXS we utilized a microfocus X-ray source with tungsten (W) anode material. In addition the proposed system eliminates tungsten's multiple spectral lines by selecting monochromator crystal size appropriately therefore eliminating need for the costly mismatched, two-crystal monochromator. The system imaging was fine-tuned for tungsten Kα1 line with the energy of 59.3 keV since it has been shown to be of great clinical significance by a number of researchers at synchrotron facilities. In this way a laboratory system that can be used for evaluating and quantifying tissue properties, initially explored at synchrotron facilities, would be of great interest to a larger research community. To demonstrate the imaging capability of our instrument we use a chicken thigh tissue sample.

First results of KALI-30 GW with 1 MV flash X-rays generation and characterization by Imaging plate

The design, development and commissioning of 1 MV pulsed electron accelerator producing Flash X-Rays is described in this paper. This pulsed power system is based on bipolar MARX generator and Blumlein followed by Explosive electron emission diode assembly. The peak pulsed power is ∼ 30 GW. The electron energies in the range of 400 keV to 1030 keV are produced and delivered to experimental load of Industrial diode. Electrons are emitted from a stainless steel ring at ground potential by explosive field emission and bombard the anode tungsten pin for flash X-rays generation. The relativistic electron beam has been simulated within the diode chamber and pattern shows the beam propagation. Imaging plates are used to characterize the source size and optimization has been reported.

TU-F-18C-07: Hardware Advances for MTF Improvement in Dedicated Breast CT

Purpose: In this study, we have designed and implemented a prototype dedicated breast CT system (bCT) to improve the spatial resolution characteristics, in order to improve detection of micro-calcifications. Methods: A 10.8 kW water-cooled, tungsten anode x-ray tube, running up to 240 mA at 60 kV, coupled with an x-ray generator specifically designed for this application, and 0.3 mm of added copper filter was used to generate x-ray pulses. A CsI CMOS flat panel detector with a pixel pitch of 0.075 mm in native binning mode was used. The system geometry was designed in a way to achieve an FOV on par with similar bCT prototypes, resulting in a magnification factor of 1.39. A 0.013 mm tungsten wire was used to generate point spread functions. Multiple scans were performed with different numbers of projections, different reconstruction kernel sizes and different reconstruction filters to study the effects of each parameter on MTF. The resulting MTFs were then evaluated quantitatively using the generated PFSs. Duplicate scans with the same parameters were performed on two other dedicated breast CT systems to compare the performance of the new prototype. Results: The results of the MTF experiments demonstrate a significant improvement in the spatial resolution characteristics. In the new prototype, using the pulsed x-ray source results in a restoration of the azimuthal MTF degradation, due to motion blurring previously seen in other bCT systems. Moreover, employing the higher resolution x-ray detector considerably improves the MTF. The MTF at 10% of the new system is at 3.5 1/mm, a factor of 4.36 greater than an earlier bCT scanner. Conclusion: The MTF analysis of the new prototype bCT shows that using the new hardware and control results in a significant improvement in visualization of finer detail. This suggests that the visualization of micro-calcifications will be significantly improved.

TU-F-18C-08: Micro-Calcification Detectability Using Spectral Breast CT Based On a Si Strip Detector

Purpose: To investigate the feasibility of micro-calcification (μCa) detectability by using an energy-resolved photon-counting Si strip detector for spectral breast computed tomography (CT). Methods: A bench-top CT system was constructed using a tungsten anode x-ray source with a focal spot size of 0.8 mm and a single line 256-pixel Si strip photon counting detector with a pixel pitch of 100 μm. The slice thickness was 0.5 mm. Five different size groups of calcium carbonate grains, from 105 to 215 μm in diameter, were embedded in a cylindrical resin phantom with a diameter of 16 mm to simulate μCas. The phantoms were imaged at 65 kVp with an Entrance Skin Air Kerma (ESAK) of 1.2, 3, 6, and 8 mGy. The images were reconstructed using a standard filtered back projection (FBP) with a ramp filter. A total of 200 μCa images (5 different sizes of μCas × 4 different doses × 10 images for each setting) were combined with another 200 control images without μCas, to ultimately form 400 images for the reader study. The images were displayed in random order to three blinded observers, who were asked to give a binary score on each image regarding the presence of μCas.more » The μCa detectability for each image was evaluated in terms of binary decision theory metrics. The sensitivity, specificity, and accuracy were calculated to study the size and dose-dependence for μCa detectability. Additionally, the influence of the partial volume effect on the μCa detectability was investigated by simulation. Results: For a μCa larger than 140 μm in diameter, detection accuracy of above 90 % was achieved with the investigated prototype spectral CT system at ESAK of 1.2 mGy. Conclusion: The proposed Si strip detector is expected to offer superior image quality with the capability to detect μCas for low dose breast imaging.« less

TU-F-18A-05: An X-Ray Fluorescence Technique for Energy Calibration of Photon-Counting Detectors

Purpose: To investigate the feasibility of energy response calibration of a Si strip photon-counting detector by using the x-ray fluorescence technique. Methods: X-ray fluorescence was generated by using a pencil beam from a tungsten anode x-ray tube with 2 mm Al filtration. Spectra were acquired at 90° from the primary beam direction with an energy-resolved photon-counting detector based on Si strips. The distances from the source to target and the target to detector were approximately 19 and 11 cm, respectively. Four different materials, containing Ag, I, Ba, and Gd, were placed in small plastic aliquots with a diameter of approximately 0.7 cm for x-ray fluorescence measurements. Linear regression analysis was performed to derive the gain and offset values for the correlation between the measured fluorescence peak center and the known energies for materials. The energy resolution was derived from the full width at half maximum (FWHM) of the fluorescence peaks. In addition, the angular dependence of the recorded fluorescence spectra was studied at 30°, 60°, and 120°. Results: Strong fluorescence signals of all four target materials were recorded with the investigated geometry for the Si strip detector. The recorded pulse height was calibrated with respect to photon energy and themore » gain and offset values were calculated to be 7.0 mV/keV and −69.3 mV, respectively. Negligible variation in energy calibration was observed among the four energy thresholds. The variation among different pixels was estimated to be approximately 1 keV. The energy resolution of the detector was estimated to be 7.9% within the investigated energy range. Conclusion: The performance of a spectral imaging system using energy-resolved photon-counting detectors is very dependent on the energy calibration of the detector. The proposed x-ray fluorescence technique provides an accurate and efficient way to calibrate the energy response of a photon-counting detector.« less

Tungsten anode spectral model using interpolating cubic splines: Unfiltered x‐ray spectra from 20 kV to 640 kV

Monte Carlo methods were used to generate lightly filtered high resolution x-ray spectra spanning from 20 kV to 640 kV. X-ray spectra were simulated for a conventional tungsten anode. The Monte Carlo N-Particle eXtended radiation transport code (MCNPX 2.6.0) was used to produce 35 spectra over the tube potential range from 20 kV to 640 kV, and cubic spline interpolation procedures were used to create piecewise polynomials characterizing the photon fluence per energy bin as a function of x-ray tube potential. Using these basis spectra and the cubic spline interpolation, 621 spectra were generated at 1 kV intervals from 20 to 640 kV. The tungsten anode spectral model using interpolating cubic splines (TASMICS) produces minimally filtered (0.8 mm Be) x-ray spectra with 1 keV energy resolution. The TASMICS spectra were compared mathematically with other, previously reported spectra. Using pairedt-test analyses, no statistically significant difference (i.e., p > 0.05) was observed between compared spectra over energy bins above 1% of peak bremsstrahlung fluence. For all energy bins, the correlation of determination (R(2)) demonstrated good correlation for all spectral comparisons. The mean overall difference (MOD) and mean absolute difference (MAD) were computed over energy bins (above 1% of peak bremsstrahlung fluence) and over all the kV permutations compared. MOD and MAD comparisons with previously reported spectra were 2.7% and 9.7%, respectively (TASMIP), 0.1% and 12.0%, respectively [R. Birch and M. Marshall, "Computation of bremsstrahlung x-ray spectra and comparison with spectra measured with a Ge(Li) detector," Phys. Med. Biol. 24, 505-517 (1979)], 0.4% and 8.1%, respectively (Poludniowski), and 0.4% and 8.1%, respectively (AAPM TG 195). The effective energy of TASMICS spectra with 2.5 mm of added Al filtration ranged from 17 keV (at 20 kV) to 138 keV (at 640 kV); with 0.2 mm of added Cu filtration the effective energy was 9 keV at 20 kV and 169 keV at 640 kV. Ranging from 20 kV to 640 kV, 621 x-ray spectra were produced and are available at 1 kV tube potential intervals. The spectra are tabulated at 1 keV intervals. TASMICS spectra were shown to be largely equivalent to published spectral models and are available in spreadsheet format for interested users by emailing the corresponding author (JMB).

Residual Stresses Comparison Determined by Short-Wavelength X-Ray Diffraction and Neutron Diffraction for 7075 Aluminum Alloy

High strength Al alloy 7075 is widely used in aeronautic and space domains. However, when the thick plate of 7075 alloy is quenched improperly, large residual stress (RS) will be produced which leads to the loss of performance in resistance corrosion, fatigue and fracture. It is necessary to get the detailed information about residual stress distribution in the quenched plate. Conventional X-ray diffraction, a viable residual stress test method, can only reveal the RS state near surface layer due to limited penetrated depth. RS in the bulk components now can usually be analyzed by neutron diffraction or hard X-ray diffraction of high energy synchrotron in non-destructive way. Here a novel non-destructive method using short-wavelength characteristic X-ray diffraction meter (SWXRD) with the X-ray tube of tungsten anode target to determine the RS within the materials is developed in China. This paper revealed the RS distribution in a 20 mm thick plate of 7075 Al alloy determined by SWXRD and typical neutron diffraction (in LLB laboratory of France). The RS distribution through the thickness of Al plate shows a good agreement with the result determined by SWXRD compared with neutron diffraction.

Modification of the TASMIP x-ray spectral model for the simulation of microfocus x-ray sources

The availability of accurate and simple models for the estimation of x-ray spectra is of great importance for system simulation, optimization, or inclusion of photon energy information into data processing. There is a variety of publicly available tools for estimation of x-ray spectra in radiology and mammography. However, most of these models cannot be used directly for modeling microfocus x-ray sources due to differences in inherent filtration, energy range and/or anode material. For this reason the authors propose in this work a new model for the simulation of microfocus spectra based on existing models for mammography and radiology, modified to compensate for the effects of inherent filtration and energy range. The authors used the radiology and mammography versions of an existing empirical model [tungsten anode spectral model interpolating polynomials (TASMIP)] as the basis of the microfocus model. First, the authors estimated the inherent filtration included in the radiology model by comparing the shape of the spectra with spectra from the mammography model. Afterwards, the authors built a unified spectra dataset by combining both models and, finally, they estimated the parameters of the new version of TASMIP for microfocus sources by calibrating against experimental exposure data from a microfocus x-ray source. The model was validated by comparing estimated and experimental exposure and attenuation data for different attenuating materials and x-ray beam peak energy values, using two different x-ray tubes. Inherent filtration for the radiology spectra from TASMIP was found to be equivalent to 1.68 mm Al, as compared to spectra obtained from the mammography model. To match the experimentally measured exposure data the combined dataset required to apply a negative filtration of about 0.21 mm Al and an anode roughness of 0.003 mm W. The validation of the model against real acquired data showed errors in exposure and attenuation in line with those reported for other models for radiology or mammography. A new version of the TASMIP model for the estimation of x-ray spectra in microfocus x-ray sources has been developed and validated experimentally. Similarly to other versions of TASMIP, the estimation of spectra is very simple, involving only the evaluation of polynomial expressions.

A first generation compact microbeam radiation therapy system based on carbon nanotube X-ray technology.

We have developed a compact microbeam radiation therapy device using carbon nanotube cathodes to create a linear array of narrow focal line segments on a tungsten anode and a custom collimator assembly to select a slice of the resulting wedge-shaped radiation pattern. Effective focal line width was measured to be 131 μm, resulting in a microbeam width of ∼300 μm. The instantaneous dose rate was projected to be 2 Gy/s at full-power. Peak to valley dose ratio was measured to be >17 when a 1.4 mm microbeam separation was employed. Finally, multiple microbeams were delivered to a mouse with beam paths verified through histology.

Correlation of x-ray emission with interferometry and neutron diagnostics at tungsten anode face and deuterium filling in plasma-focus discharge

In this paper, the influence of the tungsten evaporated from the anode on neutron production and soft x-ray radiation was studied on the base of x-ray, interferometry and neutron diagnostics performed on the plasma-focus PF-1000 device with deuterium as the filling gas at the current of 2 MA and neutron yield above 1010. In the axial center of the anode face the copper circuit plate was substituted with a tungsten one. During the pinch, the tungsten ions evaporated from the anode were transported into the plasma column. The differences in the filters used in the microchannel-plate detector X-frames and PIN detectors enabled separation of the bremsstrahlung emitted by the deuterium plasma from the recombination radiation of the tungsten ions produced in the region of the plasma column near the anode at the time of the evolution of instabilities. In comparison with the copper anode face, the neutron yield decreased to 40% and the energy of deuterons producing neutrons to 80%.

In-line phase shift tomosynthesis

The purpose of this work is to (1) demonstrate laboratory measurements of phase shift images derived from in-line phase-contrast radiographs using the attenuation-partition based algorithm (APBA) of Yan et al. [Opt. Express 18(15), 16074-16089 (2010)], (2) verify that the APBA reconstructed images obey the linearity principle, and (3) reconstruct tomosynthesis phase shift images from a collection of angularly sampled planar phase shift images. An unmodified, commercially available cabinet x-ray system (Faxitron LX-60) was used in this experiment. This system contains a tungsten anode x-ray tube with a nominal focal spot size of 10 μm. The digital detector uses CsI∕CMOS with a pixel size of 50×50 μm. The phantoms used consisted of one acrylic plate, two polystyrene plates, and a habanero pepper. Tomosynthesis images were reconstructed from 51 images acquired over a ±25° arc. All phase shift images were reconstructed using the APBA. Image contrast derived from the planar phase shift image of an acrylic plate of uniform thickness exceeded the contrast of the traditional attenuation image by an approximate factor of two. Comparison of the planar phase shift images from a single, uniform thickness polystyrene plate with two polystyrene plates demonstrated an approximate linearity of the estimated phase shift with plate thickness (-1600 rad vs -2970 rad). Tomographic phase shift images of the habanero pepper exhibited acceptable spatial resolution and contrast comparable to the corresponding attenuation image. This work demonstrated the feasibility of laboratory-based phase shift tomosynthesis and suggests that phase shift imaging could potentially provide a new imaging biomarker. Further investigation will be needed to determine if phase shift contrast will be able to provide new tissue contrast information or improved clinical performance.

Erosion and Lifetime of Tungsten, Gold, and Nichrome Wire Anodes in an Ultracorona in Air

Anode erosion rates and lifetime-limiting parameters for different wire materials are investigated in a positive corona in atmospheric pressure air. The electrode wear is determined by measuring electrical resistance of the corona wire. Among the test materials are W, Ni-Cr alloys, and Au-coated stainless steels. The erosion rate of the Au-coated stainless steel and Ni-Cr alloy anode wires increases approximately exponentially with the total amount of transferred charge. A unified linear relationship between the ozone generation rate and wire diameter is suggested for typically used materials.

SU‐E‐I‐32: A Comparison of Multi‐Detector CT Energy Spectrums for Use in Monte Carlo Simulations

Purpose: To compare two different methods of obtaining energy spectrums for use in Monte Carlo (MC) simulations of a multi‐detector CT (MDCT) scanner. Methods: The first set of CT energy spectrums were obtained by directly measuring the x‐ray tube output using an Amptek CdTe detector with a collimator. The CT x‐ray tube was fixed at the 12 o' clock position and the detector was placed on the patient table. The bowtie filters were removed from the path of the beam, and the tube current was set to 10 mA, the lowest possible setting, to minimize x‐ray fluence. Data was recorded for tube potentials of 80, 100, 120, and 140 kVp. However, the 140 kVp potential saturated the detector. The second set of CT energy spectrums was derived by utilizing a MC simulation to pass a soft tungsten anode spectrum through a proprietary beam hardening material and recording the resulting spectrum. The initial tungsten anode spectrum was obtained using an implementation of Boone and Seibert's tungsten anode spectral model. Results: The MDCT scanner uses a tungsten anode which theoretically results in a spectrum with characteristic x‐rays of 59 keV and 67 keV. The second characteristic x‐ray peak was clearly evident in all of the measured spectrums; however, the first characteristic x‐ray peak was almost nonexistent. The derived spectrums were similar to the measured spectrums in that most of the soft energy in the 30–50 keV range had been filtered out. However, both characteristic x‐rays were present in the derived spectrums. Conclusion: Different spectrums resulting from measured and derived methods suggest a machine specific spectrum should be acquired for accurate Monte Carlo patient dose evaluation. The attenuation in the measured spectrum indicates the presence of a fairly significant hardening filter which may not have been fully accounted for when developing the derived spectrums.

TH-A-103-05: Characterization of An Energy-Resolved Photon-Counting Si Strip Detector for Breast CT Imaging

Purpose: To investigate the characteristics of a high resolution energy‐resolved photon‐counting Si strip detector for breast CT imaging. Methods: A prototype Si strip detector was studied for breast CT imaging. A bench‐top CT system was constructed using a tungsten anode x‐ray source with a focal spot of 0.8 mm and a single line Si strip detector with 256 pixels and pixel pitch of 100 μm. A 38 μm diameter tungsten wire phantom was used to determine the point spread function (PSF) of the detector. The tungsten wire phantom was positioned 110 and 7.5cm from the x‐ray tube focal spot and detector, respectively. The system MTF was measured using reconstructed images. For the noise power spectrum (NPS), three different exposures 16, 31, and 46 μGy were used. Flat field images were acquired with and without electric noise at each exposure to investigate the effect of detector's electric noise on the noise property. The simulations with the same phantom and system geometry were also performed for validation purposes. A 16 cm water phantom, which contains various diameters (76, 102, 152, 203, and 254 μm) of aluminum (Al) wire was investigated to confirm the simulation and experimental results. Results: The desired resolution of 100 μm, corresponding to a spatial frequency of 5 lp/mm was demonstrated in both simulation and experimental results. A higher normalized NPS was measured when electronic noise included. The relationship between measured and known diameter for Al wires was quite linear except for the smallest Al wire which is smaller than detector pixel size. Conclusion: The performance of the prototype Si strip detector was evaluated using MTF and NPS. The results show that the investigated detector has excellent potential for high resolution breast imaging at low radiation dose levels.

TH‐A‐103‐06: Radiation Dose Reduction with Optimal Energy Weighting for a Prototype Energy‐Resolved Photon‐Counting Si Strip Detector

Purpose: To develop simulation and experimental methods for optimal energy weighting to reduce dose and enhance contrast for the detection of microcalcification, soft‐tissue lesions and iodine‐contrast objects using a prototype energy‐resolved photon‐counting Si strip CT detector. Methods: A prototype energy‐resolved photon‐counting Si strip CT detector was investigated for optimal energy weighting. The Si strip detector has 256 pixels with 100 μm pitch. It was placed in an edge‐on geometry which results in an effective attenuation length of 0.6 mm. A tungsten anode X‐ray spectrum of 65 kVp with 2 mm Al filter was used. Glandular and Adipose equivalent phantoms were constructed using PMMA and polyethylene. Water, calcium hydroxyapatite and iodine with different concentrations were used to simulate soft tissue lesion, microcalcification and contrast material in breast tissue. A simulation package was generated to reconstruct images from charge‐integrated and energy‐resolving photon‐counting detectors. Energy weighting factors based on projection and image based methods were used in the four energy bins to enhance contrast. Different energy thresholds were investigated based on iodine K‐edge, equal counts per bin, and equally spaced bins. CNR was computed to compare image quality between methods. Results: Simulation results indicate that using an optimized energy weighting image reconstruction improves CNR for water (30%–40%), for hydroxyapatite (30% –50%), and for iodine (35%–40%) in comparison of those images from charge‐integrated reconstruction. Conclusion: The implementation of energy weighting methods in image reconstruction for the prototype energy‐resolved photon‐counting Si strip CT detector can improve CNR or reduce radiation dose. This technique can potentially be used for detection of microcalcification, soft‐tissue lesions and iodine‐contrast object in a spectral breast CT system.

SU-C-116-07: Breast Density Quantification Using Liquid Phantoms with Dual-Energy Mammography

Purpose: Breast density has shown to be an important indicator for breast cancer risk. A computational calibration study using breast-equivalent liquid phantoms in dual-energy mammography is investigated to determine its feasibility and improvement in accuracy for breast density quantification. Methods: A computational model simulates a dual energy mammography system which is equipped with a tungsten anode x-ray tube and acquires dual energy images at 28 kVp with a 50 μm rhodium filter and 49 kVp with a 300 μm copper filter. Liquid phantoms, consisting of mixtures of water (H2O), glycerol (C3H6O3) and isopropyl alcohol (C3H6O) were used to simulate the X-ray attenuation properties of breast tissues. Calibration was accomplished with the simulated dual energy signals from the liquid phantoms using a rational polynomial function. The accuracy of liquid phantom calibration was tested with different phantom configurations of various thicknesses (2–8 cm) and densities (0%–100%), along with simulated glandular and adipose tissues. The performance of the liquid phantom calibration was compared to standard CIRS plastic phantom calibration by evaluating the errors in breast density quantification in simulated breast tissues. Results: Simulation results indicate that a mixture of liquid materials based on hydrogen, carbon and oxygen can be used to create glandular and adipose equivalent phantoms. For glandular and adipose tissues H2O, C3H6O3 and C3H6O percentages were estimated to be 42.68%, 22.62%, 34.69% and 0.11%, 16.37%, 83.51%, respectively. RMS errors for thicknesses were smaller (0.063 mm for glandular and 0.072 mm for adipose) using liquid phantoms than the results reported with CIRS phantoms. RMS errors for variable glandular densities were 1.93%. Conclusion: The results of this work indicate that a proper selection of liquid mixtures can be used as breast equivalent calibration phantoms in dual-energy mammography, which may potentially improve the accuracy in dual energy breast density quantification.

On a dark-field signal generated by micrometer-sized calcifications in phase-contrast mammography

We show that a distribution of micrometer-sized calcifications in the human breast which are not visible in clinical x-ray mammography at diagnostic dose levels can produce a significant dark-field signal in a grating-based x-ray phase-contrast imaging setup with a tungsten anode x-ray tube operated at 40 kVp. A breast specimen with invasive ductal carcinoma was investigated immediately after surgery by Talbot–Lau x-ray interferometry with a design energy of 25 keV. The sample contained two tumors which were visible in ultrasound and contrast-agent enhanced MRI but invisible in clinical x-ray mammography, in specimen radiography and in the attenuation images obtained with the Talbot–Lau interferometer. One of the tumors produced significant dark-field contrast with an exposure of 0.85 mGy air-kerma. Staining of histological slices revealed sparsely distributed grains of calcium phosphate with sizes varying between 1 and 40 μm in the region of this tumor. By combining the histological investigations with an x-ray wave-field simulation we demonstrate that a corresponding distribution of grains of calcium phosphate in the form of hydroxylapatite has the ability to produce a dark-field signal which would—to a substantial degree—explain the measured dark-field image. Thus we have found the appearance of new information (compared to attenuation and differential phase images) in the dark-field image. The second tumor in the same sample did not contain a significant fraction of these very fine calcification grains and was invisible in the dark-field image. We conclude that some tumors which are invisible in x-ray absorption mammography might be detected in the x-ray dark-field image at tolerable dose levels.

Characterization of Tissue-Equivalent Materials Through Measurements of the Linear Attenuation Coefficient and Scattering Profiles Obtained &lt;newline/&gt;With Polyenergetic Beams

In this work seven tissue-equivalent materials (Nylon, Polyacetate, Polymethylmethacrylate (PMMA), water, muscle-equivalent, bone-equivalent and adipose-equivalent) were characterized, through their attenuation (linear attenuation coefficient) and scattering (scattering profile) properties. An energy dispersive X-ray system (EDXS) was used to analyze these properties simultaneously. The EDXS consisted of a tungsten anode X-ray tube operating at 60 kVp, a goniometer, and two detectors: a Cadmium Telluride (CdTe) detector, positioned at 7 degrees with relation to the incident beam, used for detecting the energy distribution of the scattered photons, and a Silicon Drift Detector (SDD), positioned at zero degree with relation to the incident beam, used for detecting the energy distribution of the transmitted beam (with the sample) or the incident beam (without the sample). The preliminary results obtained in this work show the potential of combining the linear attenuation coefficient and the scattering profile for characterizing and choosing the most suitable tissue-equivalent materials to simulate human tissue. Our results show that adipose-equivalent, water and bone-equivalent would be adequate to simulate adipose, muscle and bone tissue respectively.