85 research outputs found
Cdmam_Fit_3: A Graphical User Interface for Mammographic Contrast-Detail Analysis
No full textAccording to the European Guidelines for quality control in digital mammography, mammographic image quality is expressed in terms of threshold contrast visibility using clinical exposure settings. The threshold contrast is defined as the lowest contrast value for which the objects are visible. The Contrast-Detail MAMmography (CDMAM) phantom is commonly used for the contrast-detail analysis, i.e. the detection of small thickness and low contrast objects. An automated scoring software tool (called CDCOM) was recently developed to evaluate the CDMAM radiographs. However, the CDCOM program does not determine the threshold contrast and further analysis is required by the user. This work presents a MATLAB-based graphical user interface (GUI), called CDMAM_fit_3, that a) reads and converts the original CDCOM data to a probability matrix, b) applies a psychometric curve fit to the data, c) predicts the human readout, d) compares the predicted results with the acceptable and achievable limits (provided by the European Guidelines) and e) saves the output data in various formats (i.e. txt, csv, xls, xlsx and xlsm). An executable version of the CDMAM_fit_3 can be used by the user without any programming and data processing knowledg
X-ray Performance Evaluation of the Dexela CMOS APS X-ray Detector Using Monochromatic Synchrotron Radiation in the Mammographic Energy Range
No full textDigital detectors based on complementary metaloxide-semiconductors (CMOS) active pixel sensor (APS) technology have been introduced recently in many scientific applications. This work is focused on the X-ray performance evaluation of a novel CMOS APS detector in low energy medical imaging applications using monochromatic synchrotron radiation (i.e., 17–35 keV), which also allows studying how the performance varies with energy. The CMOS sensor was coupled to a Thallium-activated structured cesium iodide (CsI:Tl) scintillator and the detector’s X-ray performance evaluation was carried out in terms of sensitivity, presampling modulation transfer function (pMTF), normalized noise power spectrum (NNPS) and the resulting detective quantum efficiency (DQE). A Monte Carlo simulation was used to validate the experimentally measured low frequency DQE. Finally, the effect of iodine’s secondary generated K-fluorescence X-rays on pMTF and DQE results was evaluated. Good agreement (within 5%) was observed between the Monte Carlo and experimentally measured low frequency DQE results. A CMOS APS detector was characterized for the first time over a wide range of low energies covering the mammographic spectra. The detector’s performance is limited mainly by the detectability of the scintillator. Finally, we show that the current data could be used to calculate the detector’s pMTF, NNPS and DQE for any mammographic spectral shape within the investigated energies
High Resolution Active Pixel Sensor X-Ray Detectors for Digital Breast Tomosynthesis
No full textCurrent large area x-ray detectors for digital breast tomosynthesis (DBT) are based on the amorphous silicon (a-Si:H) passive pixel sensor (PPS) technology. However, PPS detectors suffer from a limited resolution and high electronic noise. In this dissertation, we propose high resolution large area active pixel sensor (APS) x-ray detectors based on the complementary metal-oxide-semiconductor (CMOS) and amorphous In-Sn-Zn-O (a-ITZO) thin-film transistor (TFT) technologies to improve the imager resolution and noise properties.
We evaluated the two-dimensional (2D) x-ray imaging performance as measured by the modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) for both 75 µm (Dexela 2923 MAM) and 50 µm pixel pitch (DynAMITe) CMOS APS x-ray detectors. Excellent imaging performance (DQE in the range of 0.7 – 0.3) has been achieved over the entire spatial frequency range (0 – 6.7 mm-1) at low air kerma below 10 µGy using the 75 µm pixel pitch Dexela 2923 MAM detector. The 50 μm pixel pitch DyAMITe detector has further extended the spatial resolution of the detector to 10 mm-1 with a low electronic noise of 150 e-. Also, a 2D cascaded system analysis model has been developed to describe the signal and noise transfer for the CMOS APS x-ray imaging systems. We also implemented three-dimensional (3D) cascaded system analysis to simulated the 3D MTF, NPS and DQE characteristics using DBT radiation conditions and acquisition geometries. The 3D cascaded system analysis for the DynAMITe detector was integrated with an object task function, a medical imaging display model, and the human eye contrast sensitivity function to calculate the detectability index and area under the ROC curve (AUC). It has been demonstrated that the display pixel pitch and zoom factor should be optimized to improve the AUC for detecting high contrast objects such as microcalcifications. Also, detector electronic noise of smaller than 300 e- and a high display maximum luminance (>1000 cd/cm2) are desirable to distinguish microcalcifications of 150 µm or smaller in size. For low contrast object detection, a medical imaging display with a minimum of 12 bits gray levels is needed to realize accurate luminance levels. A wide projection angle range (≥ ±30°) combined with the image gray level magnification could improve the detectability for low contrast objects especially when the anatomical background noise is high.
CMOS APS x-ray detectors demonstrate both a high pixel resolution and low electronic noise, but are challenging to be fabricated in a large detector size greater than the wafer scale. Alternatively, current-mode APS (C-APS) based on a-ITZO TFTs was proposed for DBT due to the high gain, low noise, and capability to realize a large detector area. Specifically, we fabricated a-ITZO TFTs and achieved a high field-effect mobility of >30 cm2/Vs. We have also evaluated the electrical performance of a 50 µm pixel pitch a-ITZO TFT C-APS combined with an a-Si:H p+-i-n+ photodiode using SPICE simulation. The proposed C-APS circuit demonstrates a high charge gain of 885 with data line loadings considered. A pixel circuit layout and fabrication process have also been suggested. Finally, noise analysis has been applied to the a-ITZO TFT C-APS. A low electronic noise of around 239 e- has been established.
The research presented in this thesis indicates that APS x-ray detectors based on both CMOS and a-ITZO TFT technologies are promising for next generation DBT systems.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136983/1/zhaocm_1.pd
Damage arrest mechanisms in nanoparticle interleaved composite interfaces
No full textThe effectiveness of carbonaceous nanoparticles in arresting and delaying damage in nanocomposites has been attributed to multiscale toughening mechanisms. To explore their application in joined interfaces of composites, this study investigates the use of carbon nanotube (CNT) interleaved films for co-cured joining of composite parts and their consequent effects on the interfacial fracture toughness. Carbon nanotubes dispersed in a thermoset resin into thin films of two discrete thicknesses (200 μ and 500 μ) and three concentrations of CNT dispersion were chosen for this study (0.5% wt., 1% wt., and 2% wt.). The films were semi-cured in the oven before being incorporated as interleaves in the composite laminate interface. Fracture toughness of the interface in mode I loading conditions was determined through double cantilever beam (DCB). Micrographs of the fracture surfaces reveal a slip-and-stick based crack jump and arrest phenomena in mode I when nanoparticles are added to the interleaved interface. The thickness of the interleaves has a more significant effect on mode I toughening mechanisms than the concentration of the nanoparticles.Aerospace Structures & Computational Mechanic
Effect of dwell stage in the cure cycle on toughening of epoxy using thermoplastic multilayers
No full textEpoxies with high cross-linking densities are brittle and hence have a low fracture toughness. However, different methods are known to increase fracture toughness. Numerous approaches are known to incorporate a second phase into the epoxy matrix, such as rubber, inorganic nanoparticles or thermoplastics, referred to as bulk resin modification. These tougheners usually form specific morphologies during the curing phase of epoxy, resulting in improved fracture toughness of the system. Unfortunately, for some tougheners, the addition of second phase into the epoxy system also results in a reduction in overall modulus and limitation in end-use temperature of the system. In the case of thermoplastic tougheners, the second phase is created by diffusion and dissolution, followed by reaction induced phase separation, leading to a morphology in the micrometer range. However, the influence of the curing history beyond phase separation, using two dwell cure cycles with varying dwell time/degree of cure, on the interphase dimension and final morphology for PEI having a contrasting phase behaviour (UCST), is not well understood. The research presented in this work aims to understand the interphase formation, to later attain the desired droplet size and interphase morphology for improved material toughness. This aim is achieved by analyzing the influence of dwell time by considering two main cases for each selected 1st dwell temperature (120-180˚C): (i) wait until the onset of phase separation (OPS) before increasing the temperature to 200°C (second dwell), (ii) wait until 80% degree of cure (80% DOC) before the second dwell. At all processing temperatures, a distinct gradient morphology (Fig. 1a ) was clearly observed for both cases (OPS and 80% DOC). The SEM micrographs revealed the formation of a larger interphase region (71 μm) for the OPS case as compared to the 80% DOC case (56 μm). Figure 1b shows the interphase thickness as a function of 1st dwell temperature for both OPS and 80% DOC cases. It can be seen that the interphase thickness increased with 1st dwell temperature for both cases, until 160˚C after which it slightly decreased for a 1st dwell temperature of 180˚C. This work highlights, i) the importance of the curing process beyond phase separation to control interphase dimension and final morphology and, ii) the influence of both these parameters on the toughness enhancement.Aerospace Manufacturing Technologie
Measurement of damage growth in ultrasonic spot welded joint
No full textUltrasonic spot welding is a joining technique for thermoplastic composites with great potential regarding processing speed and cost. To investigate the damage tolerance and possible inherent damage arresting behavior of multi-spot welded joints, a technique is necessary to measure damage growth in the joints under cyclic loading. Visual inspection is not possible because the damage is not located on the outside surface and conventional techniques such as C-scan are not practical during a fatigue test because the specimen would have to be removed from the setup. This paper details a methodology for quantifying damage growth rates in singlespot welded joints using surface strain measurements made by Digital Image Correlation. This represents the first step towards developing a methodology for quantifying damage progression behavior in complex multi-spot welded joints.Structural Integrity & CompositesAerospace Structures & Computational Mechanic
Processing of Fibre Reinforced Polymers by Controlled Radical Induced Cationic Frontal Polymerisation
No full textRadical Induced Cationic Frontal Polymerisation (RICFP) has recently been proposed as a promising strategy for processing of epoxide carbon fibre reinforced polymers. Control of the local heat balance is crucial towards the production of industrial-quality composites, which is typically achieved via controlling the heat generation. In this work we present a comprehensive overview of RICFP processing of cycloaliphatic epoxide composites with enhance heat insulation. The thermal initiating compound was identified as the main component to control heat generation, which correlated well with the front velocity. A processing window was defined as function of the fibre and initiator contents and composites with to 45.8% Vf were successfully produced. Optimisation of resulting mechanical properties was made possible by optimisation of the heat balance, with matrix glass transition temperatures of up to 187°C achieved for the used cycloaliphatic system. Post-curing was found beneficial to overcome suggested inhomogeneous curing due to the dual-scale nature of fabrics.Aerospace Manufacturing Technologie
Tailoring mechanical properties of randomly oriented tape (ROT) composites: An experimental study
No full textDiscontinuous fiber composites (DFC) have properties such as notch insensitivity, short processing times, and large shaping freedom [1-3]. However, the mechanical behavior of ROT composites is less predictable compared to continuous fiber composites due to the mesoscopic heterogeneity of the material [4]. Controlling the tape alignment is a compelling approach for tailoring the mechanical properties of the ROT composites, enabling better control and prediction of the material properties such as tensile strength and stiffness [5]. However, for a successful implementation of the alignment method in industry, a fast tape alignment method is needed. In this study, a quantitative assessment has been made between three alignment methods. The methods have been evaluated in respect of the level of alignment and the manufacturing process by means of a decision-making matrix. The level of alignment of each method has been determined using computer vision on the orientation of individual tapes. The final alignment method has been selected which uses vertical mesoscopic sieves with a high aspect ratio to rotate tapes in a preferred direction during deposition. With this alignment method, ROT have been aligned at -45˚, 0˚, and +45˚ with respect to the loading direction. With these alignment tools, CF/PEEK ROT have been deposited inside a cavity followed by a consolidation cycle at 45 bar and 385˚C. The effect of alignment was examined by comparing the mechanical response of samples with: ROT, being longitudinally aligned, and a laminate of [+45˚,-45˚]s aligned pseudo-layers. The results of tensile tests showed that by aligning tapes in the longitudinal direction, the average tensile stiffness and strength increased by 145% (from 32.5 to 79.7 GPa) and 96% (from 202 to 396 MPa) respectively compared to randomly orientated tapes. These results show the potential gain in material properties and the ease of implementation of the method.Aerospace Manufacturing Technologie
Fracture toughness and performance of resistance-welded and co-bonded thermoset/thermoplastic polymer composite hybrid joints
No full textModern aerospace structures see increasing use of combinations of thermoplastic and thermoset composite components, requiring the development of efficient joining methods for dissimilar matrix materials. This study aimed to investigate the Mode I fracture toughness and performance of resistance-welded and co-bonded thermoset-thermoplastic composite joints for primary aerospace structural applications. Double cantilever beam and single lap shear trials were performed. It was found that using resistance welding, a significant improvement in the Mode I fracture toughness of approximately 360 % - 520 % over co-bonding can be achieved. Single lap shear tests did not allow any conclusion about the bond strengths due to thermoset laminate failure. Although, combined with optical microscopy of the fracture surfaces, it was possible to show that significant thermal degradation of the thermoset matrix can be avoided.Aerospace Structures & Computational Mechanic
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