186 research outputs found
Digital Mammography: From Physical Performance Evaluation To Image Quality Analysis
No full textSince the early 1990s digital X-ray detectors have been used extensively for medical imaging applications, such as Mammography, General Radiography, Computed Tomography, Tomosynthesis, Fluoroscopy, etc. The quality of a radiograph needs to be adequate to provide the required information for a given task. The primary physical parameters that affect image quality are spatial resolution, noise, and contrast. The Modulation Transfer Function (MTF) is the combination of contrast and resolution, the Noise Power Spectrum (NPS) combines the noise and resolution, and the Signal-to-Noise Ratio (SNR) expresses the ratio between signal and noise in large scale objects (i.e. at zero spatial frequency). The combination of SNR, MTF and NPS determines the Detective Quantum Efficiency (DQE) which represents the ability to visualize object details of a certain size and contrast. This study is using image simulation to estimate how the experimentally measured SNR, MTF and NPS of several digital X-ray detectors affect the mammographic image quality. The latter is measured in terms of Contrast-to-Noise Ratio (CNR) and Contrast-Detail (CD) analysis, using synthetic breast and CDMAM phantoms, respectivel
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
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
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
Financial Education and Decision Making Processes
No full textAbstractThe present paper aims to examine whether students of financial studies, who are, therefore, most likely to pursue a career in stock market, demonstrate tendenc ies of irrational behaviour during decis ion making when exposed to dilemmas.In detail, based on questions drawn from the literature of Behavioural F inance, the study attempts to explore whether biases, emotions and overall behaviour are likely to deter rational choices and also whether the acquis ition of financ ial knowledge enables generating rational thinking and decisions. The findings of the empirical research, based on a sample of 84 students, seem to support the princ iples of the Behavioural F inance theory, according to which decis ion making is contingent upon emotions that are likely to result in systematic errors
Endoscopic injection theraphy with epinephrine plus ethanolamine oleate 5% for bleeding ulcers.: Is it superior to epinephrine injection therapy?
No full textMarket orientation and regional development: Strategic and Structural issues for the agribusiness sector in Balkans
No full textIn the countries of South Eastern Europe, within the European Union, there are regions where the agri-food sector plays a vital role in socioeconomic terms.The aim of this paper is to examine the relationship between the market orientation concept and the Regional development. It explains the structure of the market from the perspective of small- and medium-sized agri-food producer organizations and discusses marketing strategy implications. Based on an extensive literature search the paper by focusing on key components of the market orientation concept such as, organizational culture, innovation, customer orientation, marketing co-ordination, coalitions and collaborations, explores their impact on regional development.Market orientation, innovation, collaboration, agri-food, regional development
Αξιολόγηση ψηφιακών ανιχνευτών ακτίνων Χ για εφαρμογές ιατρικής απεικόνισης
No full textDigital x-ray detectors are now the detector of choice in many X-ray examinations. They have been accepted into clinical practice over the past decade but there are still ongoing developments in the technology. Complementary metal oxide semiconductor (CMOS) active pixel sensors (APS) are a novel digital technology that offers advantages compared to some of the more established approaches (charge-coupled devices (CCD), thin film transistor arrays (TFT) and CMOS passive pixel sensors (PPS)). This thesis looks at the performance of these new sensors and attempts to identify their role in future medical imaging applications.Standard electro-optical and x-ray performance evaluations of two novel CMOS APS, namely the Large Area Sensor (LAS) and Dexela CMOS x-ray detector, are presented. The evaluation was made in terms of the photon transfer curve (PTC), the modulation transfer function (MTF), the normalized noise power spectrum (NNPS) and the resultant detective quantum efficiency (DQE). Modifications were introduced to extend the standard methods to overcome technical limitations. The performance of these detectors was compared to three commercial systems (Remote RadEye HR (CMOS APS), Hamamatsu C9732DK (CMOS PPS) and Anrad SMAM (a-Se TFT)) at beam qualities (28 kV for mammography and 52 kV and 74 kV for general radiography) based on the IEC standards. Both the LAS and Dexela CMOS detectors demonstrate enhanced performance. The effect of the CMOS APS inherent nonlinearity on the x-ray performance was also evaluated. Finally, the measured performance parameters were used to simulate images for different mammographic imaging tasks in order to establish possible areas of application for the new sensors. Two software phantoms (one representing a 3-D breast and the other the CDMAM test tool) were used to simulate a range of mammographic conditions. The results show that both novel CMOS APS detectors offer high image quality compared to the commercial detector systems.Οι ψηφιακοί ανιχνευτές ακτίνων Χ είναι πλέον διαδεδομένοι σε αρκετές εξετάσεις με ακτίνες Χ. Άρχισαν να χρησιμοποιούνται στην κλινική ιατρική την τελευταία δεκαετία αλλά εξακολουθούν να υπάρχουν συνεχείς εξελίξεις στην τεχνολογία. Η τεχνολογία συμπληρωματικών ημιαγωγών μεταλλικού οξειδίου (complementary metal oxide semiconductor - CMOS) με αισθητήρα ενεργού εικονοστοιχείου (active pixel sensor - APS) είναι μια νέα ψηφιακή τεχνολογία που προσφέρει πλεονεκτήματα σε σύγκριση με μερικές από τις πιο καθιερωμένες τεχνολογίες (π.χ. α) συσκευές συζευγμένου φορτίου (charge-coupled devices - CCD), β) ανιχνευτές με τρανζίστορ λεπτών υμενίων (thin film transistor - TFT) και γ) CMOS με αισθητήρα παθητικού εικονοστοιχείου (passive pixel sensor - PPS)). Η συγκεκριμένη διδακτορική διατριβή εξετάζει την απόδοση των ψηφιακών ανιχνευτών νέας τεχνολογίας και επιχειρεί να προσδιορίσει το ρόλο τους σε μελλοντικές εφαρμογές ιατρικής απεικόνισης.Πιο συγκεκριμένα, παρουσιάζονται αξιολογήσεις (με χρήση ορατών φωτονίων και ακτίνων Χ) απόδοσης δύο νέων ανιχνευτών CMOS APS, ονομαστικά Large Area Sensor (LAS) και Dexela CMOS x-ray detector. Η αξιολόγηση έγινε χρησιμοποιώντας τις παρακάτω τεχνικές: α) καμπύλη μεταφοράς φωτονίων (photon transfer curve - PTC), β) συνάρτηση μεταφοράς διαμόρφωσης (modulation transfer function - MTF), γ) κανονικοποιημένο φάσμα ισχύος θορύβου (normalized noise power spectrum - NNPS) και δ) ανιχνευτική κβαντική αποδοτικότητα (detective quantum efficiency - DQE). Έγιναν κάποιες τροποποιήσεις ώστε να επεκταθούν οι υπάρχουσες τεχνικές με σκοπό την εξάλειψη τεχνικών περιορισμών. Η απόδοση των δύο νέων ψηφιακών ανιχνευτών συγκρίθηκε με τρία εμπορικά συστήματα ψηφιακών ανιχνευτών (α) Remote HR RadEye (CMOS APS), β) Hamamatsu C9732DK (CMOS PPS) και γ) Anrad SMAM (a-Se TFT)) σε τρία φάσματα ακτίνων Χ (28 kV για μαστογραφία και 52 kV και 74 kV για γενική ακτινοδιαγνωστική) με βάση τα πρότυπα της Διεθνούς Ηλεκτροτεχνικής Επιτροπής (International Electrotechnical Commission - ΙEC). Αμφότεροι οι νέοι ψηφιακοί ανιχνευτές παρουσιάζουν υψηλή απόδοση. Επίσης αξιολογήθηκε το φαινόμενο της ενδογενούς μη-γραμμικής μεταφοράς σήματος και θορύβου των ανιχνευτών CMOS APS.Τέλος, οι πειραματικά μετρημένες παράμετροι απόδοσης των ψηφιακών ανιχνευτών χρησιμοποιήθηκαν για να προσομοιώσουν εικόνες σε συνθήκες μαστογραφίας με σκοπό να διαπιστωθούν πιθανές εφαρμογές ιατρικής απεικόνισης για τους δύο νέους ψηφιακοί ανιχνευτές. Δύο ψηφιακά ομοιώματα (το ένα αντιπροσωπεύει ένα τρισδιάστατο μοντέλο μαστού και το άλλο το εργαλείο δοκιμής CDMAM) χρησιμοποιήθηκαν για να προσομοιώσουν διάφορες μαστογραφικές συνθήκες. Τα αποτελέσματα δείχνουν ότι αμφότεροι οι νέοι ανιχνευτές CMOS APS προσφέρουν υψηλή ποιότητα εικόνας σε σύγκριση με τα εμπορικά συστήματα ανιχνευτών
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