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A number of interventional procedures such as cardiac catheterization, angiography and the deployment of endovascular devices are routinely performed using x-ray fluoroscopy. To minimize the patient’s exposure to ionizing radiation, each fluoroscopic image is acquired using a very low x-ray exposure (~ 1 uR at the detector). At such an exposure, most semiconductor-based digital flat panel detectors (FPD) are not x-ray quantum noise limited (QNL) due to the presence of electronic noise which substantially degrades their imaging performance. The goal of this thesis was to investigate how a FPD based on amorphous selenium (a-Se) with internal avalanche multiplication gain could be used for QNL fluoroscopic imaging at the lowest clinical exposures while satisfying all of the requirements of a FPD for interventional radiology. Towards this end, it was first determined whether a-Se can reliably provide avalanche multiplication gain in the solid-state. An experimental method was developed which enabled the application of sufficiently large electric field strengths across the a-Se. This method resulted in avalanche gains as high as 10000 at an applied field of 105 V/um using optical excitation. This was the first time such high avalanche gains have been reported in a solid-state detector based on an amorphous material. Secondly, it was investigated how the solid-state a-Se avalanche detector could be used to image X-rays at diagnostic radiographic energies (~ 75 kVp). A dual-layered direct-conversion FPD architecture was proposed. It consisted of an x-ray drift region and a charge avalanche multiplication region and was found to eliminate depth-dependent gain fluctuation noise. It was shown that electric field strength non-uniformities in the a-Se do not degrade the detective quantum efficiency (DQE). Lastly, it was determined whether the solid-state a-Se avalanche detector satisfies all of the requirements of interventional radiology. Experimental results have shown that the total noise produced by the detector is negligible and that QNL operation at the lowest fluoroscopic exposures is indeed possible without any adverse effects occurring at much larger radiographic exposures. In conclusion, no fundamental obstacles were found preventing the use of avalanche a-Se in next-generation solid-state QNL FPDs for use in interventional radiology.

A number of interventional procedures such as cardiac catheterization, angiography and the deployment of endovascular devices are routinely performed using x-ray fluoroscopy. To minimize the patient’s exposure to ionizing radiation, each fluoroscopic image is acquired using a very low x-ray exposure (~ 1 uR at the detector). At such an exposure, most semiconductor-based digital flat panel detectors (FPD) are not x-ray quantum noise limited (QNL) due to the presence of electronic noise which substantially degrades their imaging performance. The goal of this thesis was to investigate how a FPD based on amorphous selenium (a-Se) with internal avalanche multiplication gain could be used for QNL fluoroscopic imaging at the lowest clinical exposures while satisfying all of the requirements of a FPD for interventional radiology. Towards this end, it was first determined whether a-Se can reliably provide avalanche multiplication gain in the solid-state. An experimental method was developed which enabled the application of sufficiently large electric field strengths across the a-Se. This method resulted in avalanche gains as high as 10000 at an applied field of 105 V/um using optical excitation. This was the first time such high avalanche gains have been reported in a solid-state detector based on an amorphous material. Secondly, it was investigated how the solid-state a-Se avalanche detector could be used to image X-rays at diagnostic radiographic energies (~ 75 kVp). A dual-layered direct-conversion FPD architecture was proposed. It consisted of an x-ray drift region and a charge avalanche multiplication region and was found to eliminate depth-dependent gain fluctuation noise. It was shown that electric field strength non-uniformities in the a-Se do not degrade the detective quantum efficiency (DQE). Lastly, it was determined whether the solid-state a-Se avalanche detector satisfies all of the requirements of interventional radiology. Experimental results have shown that the total noise produced by the detector is negligible and that QNL operation at the lowest fluoroscopic exposures is indeed possible without any adverse effects occurring at much larger radiographic exposures. In conclusion, no fundamental obstacles were found preventing the use of avalanche a-Se in next-generation solid-state QNL FPDs for use in interventional radiology.

A number of QA procedures have been developed for Breast Brachytherapy treatments, yet none guarantee accurate dose delivery or allow conformation of the actual source position leading to errors sometimes going unnoticed. The objective of this study is to track the exact path the HDR source would follow in real time. The exit radiation of the HDR source was used to image a well defined matrix of markers. The images were acquired using FPD and were processed to obtain projection coordinates while an x-ray calibration image was processed to obtain marker coordinates. Each marker along with its projection represents a line in 3D. A mathematical solution for the ‘near-intersection’ of two 3D lines was implemented and used to determine the ‘true’ 3D source position. A matrix with N markers will produce N*(N-1)/2 points of intersection and their mean will result in a more accurate source position. This study has proved that the accuracy of source position detection using a FPD is sub-millimeter.

Abstract This study concludes the position feedback from discussing about the trend of the evolution of flat panel display ¡]FPD¡^technology by using the path dependence theory. Based on this theory, the research on the valuation curve of application forms the model of valuable development. Therefore, the position feedback of FPD technology is established according to the system dynamic theory. The key factors of position feedback are defined as below: ¡]1¡^The ages of digital TV, ¡]2¡^Light¡Bthin¡Bshort¡Bsmall¡Brapid ¡]3¡^ Good quality of CRT¡]4¡^Low cost¡]5¡^Market scale¡K etc.. It explains the character of every key factor of path dependence for FPD. In accordance with the application of valuation curve, FPD is classified into six types¡GLCD¡BPDP¡BLCOS¡BDLP¡BFED and OLED. The classification is also based on JPRI(Japan picture research institute) standard¡G ¡]1¡^the way of luminescence¡]2¡^ the size of screen¡]3¡^ the outward appearance¡]4¡^ weight¡]5¡^ Brightness¡]6¡^ Contrast Ratio¡]7¡^ View Angle¡]8¡^ Resolution¡]9¡^ response time¡]10¡^ consume power¡]11¡^ life time¡]12¡^ flexibility¡]13¡^ product application scope etc. Use the weighted index method to calculate the sum of valuation for six types of FPD technology. Drawing a valuation curve by weighted index¡]Y axis¡^ and time table(X axis). The conclusions of this study are as follows: 1. FPD technology has the obvious tendency of the path dependence. 2. By the path dependence theory, the technology of FED and OLED have potential for replacing the LCD-TFT technology. The conclusions above are significant to the management in the following prospects. 1.The mode of position feedback of high technology industry will have many references for the developmental path of industry. 2.Based on Taiwan¡¦s photo-electric industry, it is necessary to penetrate the tendency of Japan¡¦s research in order to promote the FPD industry in Taiwan. Key word¡Gpath dependence¡Bsystem dynamic theory¡Bflat panel display

Η διπλωματική αυτή εργασία ξεκινά με μια σύντομη αναφορά, στο κεφάλαιο 1, στις εξελίξεις που αφορούν τους διάφορους τρόπους ανίχνευσης της ακτινοβολίας, μετά από την αλληλεπίδρασή τους με το σώμα, και στην τεχνολογία απόκτησης ακτινοδιαγνωστικών εικόνων μέχρι την εισαγωγή της ψηφιακής απεικόνισης. Αναφέρεται, επίσης, η μετάβαση από το σύστημα φθορίζουσας οθόνης-φιλμ στο σύστημα του ενισχυτή εικόνας-tv monitor, στο σύστημα CCDs-tv camera και από εκεί στα συστήματα των επίπεδων ανιχνευτών. Στη συνέχεια, παρουσιάζονται τα πλεονεκτήματα της ψηφιακής απεικόνισης και πώς αυτά οδήγησαν στα σύγχρονα ψηφιακά συστήματα ακτινοδιαγνωστικής. Μετά την περιγραφή των συστημάτων αυτών, ακολουθεί η κατηγοριοποίησή τους ανάλογα με την τεχνολογία ανίχνευσης και πιο συγκεκριμένα ανάλογα με το σχήμα του ανιχνευτή, τον τύπο του συστήματος ανίχνευσης και τον τρόπο ανίχνευσης. Το κεφάλαιο 2 αφορά κυρίως τους επίπεδους ανιχνευτές. Αφού παρουσιάζεται η διαδικασία ανάγνωσης σε πίνακα ενεργού μήτρας, αναλύονται οι αρχές άμεσης και έμμεσης ανίχνευσης και οι παράμετροι που χαρακτηρίζουν την απόδοση ενός επίπεδου ανιχνευτή. Ολοκληρώνοτας το κεφάλαιο αυτό, γίνεται σύγκριση μεταξύ των δύο προαναφερθέντων επίπεδων ανιχνευτών, σύγκριση μεταξύ των ανιχνευτών έμμεσης ανίχνευσης, που χρησιμοποιούνται σε κλινικές εφαρμογές, και του ενισχυτή εικόνας, που τείνει να αντικατασταθεί σχεδόν σε όλα τα σύγχρονα μηχανήματα, και, τέλος, αναφορά σε διάφορες εξελίξεις πάνω στην τεχνολογία των επίπεδων ανιχνευτών. Τα συστήματα των επίπεδων ανιχνευτών εφαρμόζονται ήδη σε μια μεγάλη γκάμα ακτινοδιαγνωστικών συστημάτων, στα οποία πραγματοποιούνται εξετάσεις, όχι μόνο διάγνωσης, αλλά και θεραπείας. Εξετάσεις όπως η αγγειογραφία, η ψηφιακή αφαιρετική αγγειογραφία (DSA), στεφανιογραφία και αγγειοπλαστική περιγράφονται στο κεφάλαιο 3. Εκτός, όμως, από τα οφέλη που προκύπτουν από τις παραπάνω διαδικασίες, είναι πιθανό να προκληθούν και βλαβερές συνέπειες από την έκθεση του ασθενούς στις ακτίνες Χ. Αφού περιγραφούν τα ντετερμινιστικά και στοχαστικά αποτελέσματα των ακτινοβολιών στον άνθρωπο, αναφέρονται κάποιες δοσιμετρικές έννοιες και κάποιες συναρτησιακές σχέσεις μεταξύ τους, που σχετίζονται με τα παραπάνω αποτελέσματα και την πρόληψή τους. Η παρούσα εργασία, συνεχίζεται με το ειδικό μέρος, στο οποίο γίνεται, αρχικά, στο κεφάλαιο 4, μία σύντομη περιγραφή του ψηφιακού συστήματος στεφανιογραφίας και μία εισαγωγή σε δοσιμετρικές και γεωμετρικές έννοιες που θα χρησιμοποιηθούν στο επόμενο κεφάλαιο. Το κεφάλαιο 5 αναφέρεται, εξ’ ολοκλήρου, στο σύστημα του ψηφιακού στεφανιογράφου. Μετά την αναφορά στην παλμική ακτινοσκόπηση, τα modes απεικόνισης fluoroscopy και cine, ακολουθεί περιγραφή της τοποθέτησης των δοσιμέτρων, της γεωμετρίας και των προγραμμάτων του συστήματος, που χρησιμοποιήθηκαν για την καταγραφή του ρυθμού δόσης στην είσοδο του ασθενούς. Παρουσιάζονται τ’ αποτελέσματα και οι γραφικές παραστάσεις αυτών, καθώς και τα σχόλια που σχετίζονται με τη δοσιμετρία. Με την ολοκλήρωση των σχολίων συτών, γίνεται μετάβαση στην ποιότητα εικόνας (διακριτική ικανότητα υψηλής και χαμηλής αντίθεσης) και τη συσχέτισή της με τη δοσιμετρία. Η διπλωματική εργασία ολοκληρώνεται, κεφάλαιο 6, με διάφορους μελλοντικούς στόχους που προέκυψαν κατά τη διάρκεια της εκπόνησής της. / -

The a. c. thin film electroluminescent (ACTFEL) devices are of scientific interest due to their applications in large area, flat panel displays. Of particular interest to the research community is the mechanism of electron transport and luminance in these devices. Toward this end, a physical model and a mathematical model for SrS:Cu ACTFEL Devices were developed and published earlier by our group. The purpose of this thesis is to obtain a qualitative and quantitative match between experiment and theory. A brief summary of the model can be found here [1]. Effects of variation in drive parameters in experimental steady state measurements, and analysis of VIL (Voltage-Current-Luminance) plots for different simulated device and drive parameters are performed. The effects of voltage amplitude, activator concentration, interface energy levels, and critical field for dipole collapse were studied. The plots matched qualitatively in that all major experimental features were produced in the simulated waveforms. The measured and the simulated peak currents are 72.5 mA/cm2 and 66.42 mA/cm2 for VA = 123 V. Experimental and theoretical charge transferred per pulse were 2.75 C/cm2 and 2.26 C/cm2. Peak experimental and simulated luminance values for VA = 123 V were 531 cd/m2 and 49150 cd/m2. Total experimental and simulated luminance values for VA = 123 V case were 6.2 cd/m2 and 561.2 cd/m2 respectively. The large difference is attributed to the loss factors such as optical losses (due to total internal reflection), scattering of electrons by impurities in the bulk phosphor layer, and concentration quenching; these have not been incorporated in the model yet.

The purpose of this thesis is to contribute to the understanding of SrS based ACTFEL devices. Better understanding of the processes in the host phosphor will give us the possibility to design more efficient blue emitting ACTFEL devices. Towards this aim, a physical model, that describes the optoelectronic processes taking place in the phosphor, was developed and analytical equations were written. The analytical model was numerically simulated and the plots of flux flowing through the device and luminance output by the device were obtained. Experiments were performed to obtain the plots of current flowing through the device and luminance output by the device. These plots were then qualitatively compared and the results of comparisons are presented. The numerical simulations qualitatively verify the accuracy of the model. The drive parameters were varied in order to study its effect on the VIL characteristics of the device. On varying the voltage applied to the device and its rise and fall times, a good insight was obtained into device behavior. Simulations were also performed to obtain responses to qualitatively match the experimentally obtained responses. Various What-If scenarios have been studied by varying the device parameters. These studies have indicated the importance of these parameters in determining device performance.

This master thesis evaluated the performance of a micro-CT system consisting of Hamamatsu microfocus X-ray source L10951-04 and CMOS flat panel C7942CA-22. The X-ray source and flat panel have been characterised in terms of dark current, image noise and beam profile. Additionally, the micro-CT system’s spatial resolution, detector lag and detector X-ray response have been measured. Guidance for full image correction and methods for characterisation and performance test of the X-ray source and detector is presented. A spatial resolution of 7 lp/mm at 10 % MTF was measured. A detector lag of 0.3 % was observed after ten minutes of radiation exposure. The performance of the micro-CT system was found to be sufficient for high resolution X-ray imaging. However, the detector lag effect is strong enough to reduce image quality during subsequent image acquisition and must either be avoided or corrected for.