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The CMS Tracker is an all silicon detector and it is the biggest of its kind to be built. The system consists of over 15,000 individual detector modules giving rise to readout through almost 107 channels. The data generated by the Tracker system is close to 650 MB at 40 MHz. This has created a challenge for the CMS collaborators in terms of data storage for analysis. To store only the interesting physics data the readout rate has to be reduced to 100 Hz where the data has to be ltered through a monitoring system for quality checks. The Tracker being the closest part of the detector to the interaction point of the CMS creates yet another challenge that needs the data quality monitoring system. As it operates in a very hostile environment the silicon detectors used to detect the particles will be degraded. It is very important to monitor the changes in the sensor behaviour with time so that to calibrate the sensors to compensate for the erroneous readings. This thesis discusses the development of a monitoring system that will enable the checking of data generated by the tracker to address the issues discussed above. The system has two parts, one dealing with the data used to monitor the Tracker and a second one that deals with statistical methods used to check the quality of the data.

The SCT is a silicon strip detector forming a part of the tracking system of the ATLAS experiment at the LHC. The tracking performance of SCT is influenced by several fundamental effects: multiple scattering, Lorentz drift, energy loss variation, noise occupancy, and δ-ray production. In this thesis, the task requested by the SCT detector group has been performed. Clusters containing a δ-ray, which are assigned to a track were studied on data samples, specially prepared for this purpose. A correction to the affected cluster positions was successfully developed. The correction to δ-rays has been implemented into the ATHENA reconstruction framework and its performance was evaluated. A meaningful usage of correction for the detector alignment has been proposed. The ongoing detailed verification of the performance within the event reconstruction is partially beyond the scope of the thesis work.

Digital imaging systems for medical applications must bebased upon highly efficient detectors to ensure low patientdose. This is particularly important in screening mammographybecause of the large number healthy women that is examined. Amammography system must also provide high spatial and contrastresolution. Different approaches are compared in this thesis,and it is argued that a system based on photon countingdetectors in a scanned multi-slit geometry provides aperformance superior to established technologies. The system is realized using silicon strip detectorsirradiated at a small angle relative to the wafer surface,thereby offering large absorption depth. A linear pixelarray isscanned across the breast to obtain the complete image.Pulse-processing electronics rejecting all detector andelectronics noise count the number of photons that aredetected, forming the pixel values of the image. Optimization of the detector design is discussed in detail.The detector has been carefully simulated to investigate chargemotion and signal formation after photoninteraction. Based onthese simulations, the impact of the detector characteristicson the image quality has been evaluated. Detectors have been manufactured and evaluated both assingle components and as part of experimental imaging devicesincluding custom readout electronics. Presented in this thesisare the measured detector characteristics including a verifi-cation of charge collection efficiency and confirmation thatthe quantum efficiency is 90% for a typical mammographyspectrum. Modulation transfer functions and noise power spectrawere recorded and the detective quantum efficiency calculated.A prototype mammography system was also assembled and themodulation transfer function recorded. The interpretation ofthe modulation transfer function and detective quantumefficiency is discussed for digital systems in general and fora scanned multi-slit system in particular. <b>Keywords:</b>x-ray, imaging, silicon, detector, digital,mammography, scanning, photon counting.

<p>Digital imaging systems for medical applications must bebased upon highly efficient detectors to ensure low patientdose. This is particularly important in screening mammographybecause of the large number healthy women that is examined. Amammography system must also provide high spatial and contrastresolution. Different approaches are compared in this thesis,and it is argued that a system based on photon countingdetectors in a scanned multi-slit geometry provides aperformance superior to established technologies.</p><p>The system is realized using silicon strip detectorsirradiated at a small angle relative to the wafer surface,thereby offering large absorption depth. A linear pixelarray isscanned across the breast to obtain the complete image.Pulse-processing electronics rejecting all detector andelectronics noise count the number of photons that aredetected, forming the pixel values of the image.</p><p>Optimization of the detector design is discussed in detail.The detector has been carefully simulated to investigate chargemotion and signal formation after photoninteraction. Based onthese simulations, the impact of the detector characteristicson the image quality has been evaluated.</p><p>Detectors have been manufactured and evaluated both assingle components and as part of experimental imaging devicesincluding custom readout electronics. Presented in this thesisare the measured detector characteristics including a verifi-cation of charge collection efficiency and confirmation thatthe quantum efficiency is 90% for a typical mammographyspectrum. Modulation transfer functions and noise power spectrawere recorded and the detective quantum efficiency calculated.A prototype mammography system was also assembled and themodulation transfer function recorded. The interpretation ofthe modulation transfer function and detective quantumefficiency is discussed for digital systems in general and fora scanned multi-slit system in particular.</p><p><b>Keywords:</b>x-ray, imaging, silicon, detector, digital,mammography, scanning, photon counting.</p>

Computed tomography (CT) is a widely used medical imaging modality. By rotating an x-ray tube and an x-ray detector around the patient, a CT scanner is able to measure the x-ray transmission from all directions and form an image of the patient’s interior. CT scanners in clinical use today all use energy-integrating detectors, which measure the total incident energy for each measurement interval. A photon-counting detector, on the other hand, counts the number of incoming photons and can in addition measure the energy of each photon by comparing it to a number of energy thresholds. Using photon- counting detectors in computed tomography could lead to improved signal-to-noise ratio, higher spatial resolution and improved spectral imaging which allows better visualization of contrast agents and more reliable quantitative measurements. In this Thesis, the feasibility of using a photon-counting silicon-strip detector for CT is investigated. In the first part of the Thesis, the necessary performance requirements on such a detector is investigated in two different areas: the detector element homogeneity and the capability of handling high photon fluence rates. A metric of inhomogeneity is proposed and used in a simulation study to evaluate different inhomogeneity compensation methods. Also, the photon fluence rate incident on the detector in a scanner in clinical use today is investigated for different patient sizes through dose rate measurements together with simulations of transmission through patient im- ages. In the second part, a prototype detector module is used to demonstrate new applications enabled by the energy resolution of the detector. The ability to generate material-specific images of contrast agents with iodine and gadolinium is demonstrated. Furthermore, it is shown theoretically and ex- perimentally that interfaces in the image can be visualized by imaging the so-called nonlinear partial volume effect. The results suggest that the studied silicon-strip detector is a promising candidate for photon-counting CT.

Spectral computed tomography with energy-resolving detectors has a potential to improve the detectability of images and correspondingly reduce the radiation dose to patients by extracting and properly using the energy information in the broad x-ray spectrum. A silicon photon-counting detector has been developed for spectral CT and it has successfully solved the problem of high photon flux in clinical CT applications by adopting the segmented detector structure and operating the detector in edge-on geometry. The detector was evaluated by both the simulation and measurements. The effects of energy loss and charge sharing on the energy response of this segmented silicon strip detector with different pixel sizes were investigated by Monte Carlo simulation and a comparison to pixelated CdTe detectors is presented. The validity of spherical approximations of initial charge cloud shape in silicon detectors was evaluated and a more accurate statistical model has been proposed. A photon-counting energy-resolving application specific integrated circuit (ASIC) developed for spectral CT was characterized extensively by electrical pulses, pulsed laser and real x-ray photons from both the synchrotron and an x-ray tube. It has been demonstrated that the ASIC performs as designed. A noise level of 1.09 keV RMS has been measured and a threshold dispersion of 0.89 keV RMS has been determined. The count rate performance of the ASIC in terms of count loss and energy resolution was evaluated by real x-rays and promising results have been obtained. The segmented silicon strip detector was evaluated using synchrotron radiation. An energy resolution of 16.1% has been determined with 22 keV photons in the lowest flux limit, which deteriorates to 21.5% at an input count rate of 100 Mcps mm−2. The fraction of charge shared events has been estimated and found to be 11.1% for 22 keV and 15.3% for 30 keV. A lower fraction of charge shared events and an improved energy resolution can be expected by applying a higher bias voltage to the detector. / <p>QC 20121123</p>

The goal in medical x-ray imaging is to obtain the image quality requiredfor a given detection task, while ensuring that the patient dose is kept as lowas reasonably achievable. The two most common strategies for dose reductionare: optimizing incident x-ray beams and utilizing energy informationof transmitted beams with new detector techniques (spectral imaging). Inthis thesis, dose optimization schemes were investigated in two x-ray imagingsystems: digital mammography and computed tomography (CT). In digital mammography, the usefulness of anti-scatter grids was investigatedas a function of breast thickness with varying geometries and experimentalconditions. The general conclusion is that keeping the grid is optimalfor breasts thicker than 5 cm, whereas the dose can be reduced without a gridfor thinner breasts. A photon-counting silicon-strip detector developed for spectral mammographywas characterized using synchrotron radiation. Energy resolution, ΔE/Ein, was measured to vary between 0.11-0.23 in the energy range 15-40 keV, which is better than the energy resolution of 0.12-0.35 measured inthe state-of-the-art photon-counting mammography system. Pulse pileup hasshown little effect on energy resolution. In CT, the performance of a segmented silicon-strip detector developedfor spectral CT was evaluated and a theoretical comparison was made withthe state-of-the-art CT detector for some clinically relevant imaging tasks.The results indicate that the proposed photon-counting silicon CT detector issuperior to the state-of-the-art CT detector, especially for high-contrast andhigh-resolution imaging tasks. The beam quality was optimized for the proposed photon-counting spectralCT detector in two head imaging cases: non-enhanced imaging and Kedgeimaging. For non-enhanced imaging, a 120-kVp spectrum filtered by 2half value layer (HVL) copper (Z = 29) provides the best performance. Wheniodine is used in K-edge imaging, the optimal filter is 2 HVL iodine (Z = 53)and the optimal kVps are 60-75 kVp. In the case of gadolinium imaging, theradiation dose can be minimized at 120 kVp filtered by 2 HVL thulium (Z =69). / <p>QC 20160401</p>

In dieser Dissertationen werden Untersuchungen zur Verwendung von Klebstoffen auf der Oberfläche von Silizium-Streifen-Sensoren für die Konstruktion von Detektormodulen für das ATLAS Phase-II Upgrade vorgestellt. Drei UV-härtende Klebstoffe wurden im Vergleich zu dem derzeitigen Standard-Klebstoff an 60 ATLAS07 Miniatur-Sensoren getestet. Der Einfluss von Bestrahlung auf die chemische Zusammensetzung aller verwendeten Klebstoffe wurde unter Verwendung von Standardmethoden zur chemischen Analyse untersucht. Mithilfe der Gaschromatographie-Massenspektrometrie-Analysen von Klebstoffproben-Extrakten wurden verschiedene Ausmaße von Molekülvernetzung und gelösten Molekülbindungen festgestellt und der Grad von Strahlenhärte aller untersuchten Klebstoffe quantifiziert. Mithilfe einer Sensor-Probestation wurden die elektrischen Eigenschaften von teilweise mit Kleber bedeckten Sensoren untersucht. Im Vergleich zu Sensoren vor dem Bekleben zeigten mit Klebstoff bedeckte Sensoren einen erhöhten Leckstrom, erhöhte Zwischen-Streifen-Kapazitäten sowie Durchbrüche des Leckstroms bei niedrigeren angelegten Spannungen. Messungen der Ladungssammlungseffizienz in einem Beta-Strahlungs-Teststand wurden verwendet um den Einfluss von aufgetragenen Klebstoffen auf das Silizium-Kristallgitter zu untersuchen. Alle getesteten Sensoren - mit und ohne aufgebrachtem Klebstoff - zeigten vergleichbare Ladungssammlungseffizienzen sowie Signal-Rausch-Verhältnisse oberhalb des geforderten Minimums von zehn bei der vorhergesehenen Verarmungsspannung. Untersuchungen von Sensoren in Teststrahlmessungen zeigten außerdem, dass Sensoren um die zum Drahtbonden verwendeten Aluminiumflächen ungleichmäßig Ladung sammelten. Weiterführende Messungen konnten bestätigen, dass durch die Aluminiumflächen und darunterliegende Dotierungen das elektrische Feld innerhalb des Sensors verändert und zusätzliche Ladung um die Drahtbond-Flächen gesammelt wurde. / This thesis presents studies investigating the use of adhesives on the active area of silicon strip sensors for the construction of silicon strip detector modules for the ATLAS Phase-II Upgrade. 60 ATLAS07 miniature sensors were tested using three UV cure glues in comparison with the current baseline glue. The impact of irradiation on the chemical composition of all adhesives under investigation was studied using three standard methods for chemical analysis. Gas chromatography combined with mass spectrometry analyses of glue sample extracts showed molecule cross-linking and broken chemical bonds to different extents and allowed to quantify the radiation hardness of the adhesives under investigation. Probe station measurements were used to investigate electrical characteristics of sensors partially covered with adhesives. The presence of glue on the active sensor area was found to increase the sensor leakage current and inter-strip capacitance and frequently led to early sensor breakdowns. Charge collection efficiency measurements in a $\beta$-source setup were used to study the influence of adhesives on the silicon bulk. All sensors under investigation showed equivalent charge collection efficiencies for sensors with and without glue, as well as signal-to-noise ratios above the required minimum of ten for the foreseen bias voltage. During testbeam studies, sensor strips were found to respond inhomogeneously in bond pad regions. Follow-up measurements confirmed that the presence of bond pads affects the electric field within a sensor and leads to additional charge being collected around bond pads.

The upgrade of the Large Hadron Collider into the High Luminosity Large Hadron Collider requires a complete replacement of the ATLAS Inner Detector by a new all-silicon Inner Tracker. For this reason a new micro-strip sensor type n+ -in-p was developed. These sensors are expected to have many advantages, such as higher radiation resistance, the ability to operate even if not fully de- pleted and faster response. The main purpose of this thesis is to study and evaluate the detection performance and radiation hardness of the n+ -in-p sen- sor type with the help of electrical characteristics performed on the delivered sensors. The obtained results are compared to the Market Survey Step-2 require- ments and in the case of the sensors designed for the ATLAS Inner Tracker also to the corresponding Technical Specification document. 1