Following the development of detector technology, remote sensing image detection is being implemented with charge-coupled devices (CCD), which have promising features. The French SPOT system is the first civilian satellite sensor employing a CCD in its detection unit. In order to obtain the system transfer function (TF), a linear system model is developed in the across- and along-track directions. The overall system TF, including pixel sampling effects, is then used in the Wiener filter function to derive an optimal restoration function. A restoration line spread function (RLSF) is obtained by the inverse Fourier transform of the Wiener filter and multiplied with a window function. Simulation and empirical tests are described comparing the RLSF to standard kernels used for image resampling for geometric correction. The RLSF results in superior edge enhancement as expected.

Résumé : En tomographie d'émission par positrons (TEP), les données sont enregistrées par la détection de paires de photons de haute énergie (511~keV) en coïncidence. Or, dans un système de détection pixélisé, comme celui des scanners LabPET, la diffusion Compton dans les cristaux voisins entraîne la détection fréquente d'événements multiples, présentement rejetés dans le processus de reconstruction des images. Ces événements multiples peuvent augmenter l'efficacité de détection du scanner de façon significative, mais il reste à démontrer que l'inclusion de ces coïncidences peut améliorer la sensibilité sans affecter les critères de qualité des images, tels que la résolution spatiale et le contraste. Le but du projet est de démontrer l'influence de l'inclusion de ces événements dans le processus de reconstruction d'images. Les méthodes à critères fixes seront utilisées pour sélectionner les coïncidences triple obtenues à partir de données simulées à l’aide du logiciel de simulation GATE (« Geant4 Application for Tomographic Emission ») et de mesures réelles effectuées sur les scanners LabPET. // Abstract : In positron emission tomography, data are acquired by detecting pairs of high energy photons (511 keV) in coincidence. Thus, in a highly pixelated system such as the LabPET scanner, Compton diffusion in neighboring crystals can trigger the detection of multiple events (multiple coincidences) which are currently rejected from the reconstruction process. These multiple events can increase significantly the scanner’s detection efficiency, but it remains to be demonstrated that they can be used to increase sensitivity in the images without decreasing image quality criteria, such as the spatial resolution and contrast. The goal of this work is to demonstrate the influence of including these events in the image reconstruction process. Fixed criteria methods were used to select triple coincidences obtained from simulated data from the GATE (Geant4 Application for Tomography Emission) software and real measurements from the LabPET scanner.

Excessive imaging doses from repeated scans and poor image quality mainly due to scatter contamination are the two bottlenecks of cone-beam CT (CBCT) imaging. This study investigates a method that combines measurement-based scatter correction and a compressed sensing (CS)-based iterative reconstruction algorithm to generate scatter-free images from low-dose data. Scatter distribution is estimated by interpolating/extrapolating measured scatter samples inside blocked areas. CS-based iterative reconstruction is finally carried out on the under-sampled data to obtain scatter-free and low-dose CBCT images. In the tabletop phantom studies, with only 25% dose of a conventional CBCT scan, our method reduces the overall CT number error from over 220 HU to less than 25 HU, and increases the image contrast by a factor of 2.1 in the selected ROIs. Dual-energy CT (DECT) is another important application of CBCT. DECT shows promise in differentiating materials that are indistinguishable in single-energy CT and facilitates accurate diagnosis. A general problem of DECT is that decomposition is sensitive to noise in the two sets of projection data, resulting in severely degraded qualities of decomposed images. The first study of DECT is focused on the linear decomposition method. In this study, a combined method of iterative reconstruction and decomposition is proposed. The noise on the two initial CT images from separate scans becomes well correlated, which avoids noise accumulation during the decomposition process. To fully explore the benefits of DECT on beam-hardening correction and to reduce the computation cost, the second study is focused on an iterative decomposition method with a non-linear decomposition model for noise suppression in DECT. Phantom results show that our methods achieve superior performance on DECT imaging, with respect to noise reduction and spatial resolution.

Η υπολογιστική τομογραφία διπλής ενέργειας είναι μια σύγχρονη και συνεχώς εξελισσόμενη τεχνική, η οποία ενισχύει την διαφοροποίηση υλικών, βασιζόμενη στις φασματικές τους ιδιότητες. Φασματική απεικόνιση στην υπολογιστική τομογραφία απαιτεί τη χρήση δυο διαφορετικών ενεργειακών φασμάτων, και μπορεί να διαχωρίσει υλικά τα οποία διαφέρουν σημαντικά στον ατομικό τους αριθμό. Για το λόγο αυτό το ιώδιο (Ζ=53), το οποίο χρησιμοποιείται ως σκιαγραφική ουσία, καθώς και το οστό και οι ασβεστώσεις, τα οποία περιέχουν ασβέστιο (Ζ=20) σε μεγάλο ποσοστό, μπορούν να είναι διακριτά από τα υπόλοιπα στοιχεία τα οποία αποτελούν το ανθρώπινο σώμα, όπως υδρογόνο (Ζ=1), οξυγόνο (Ζ=8), άνθρακα (Ζ=6) και άζωτο (Ζ=7), τα οποία είναι υλικά χαμηλού ατομικού αριθμού. Αυτή τη στιγμή υπάρχουν τρεις διαφορετικές τεχνολογίες υπολογιστικής τομογραφίας διπλής ενεργείας. Ο τομογράφος με ανιχνευτή δυο στρωμάτων, ο οποίος χρησιμοποίει μια λυχνία ακτίνων Χ και ένα ανιχνευτή με δύο στρώματα σπινθηρισμού τοποθετημένα το ένα πάνω στο άλλο. Το πάνω στρώμα απορροφά τα μεγαλύτερο μέρος φωτονίων χαμηλής ενέργειας, ενώ το κάτω τα εναπομείναντα φωτόνια υψηλής ενέργειας, κάνοντας λήψη δυο σειρών δεδομένων διαφορετικών ενεργειών ταυτόχρονα. Η δεύτερη τεχνολογική προσέγγιση είναι μέσω ταχύτατης εναλλαγής της τάσης της λυχνίας. Με αυτό τον τρόπο γίνεται λήψη δυο σειρών δεδομένων διαφορετικών ενεργειών, μεταβάλλοντας τη τάση της λυχνίας από χαμηλή σε υψηλή μέσα σε μια μόνο περιστροφή. Τέλος ο τρίτος υπολογιστικός τομογράφος διπλής ενεργείας, ο οποίος χρησιμοποιείται και σε αυτή τη μελέτη, είναι ο τομογράφος δύο λυχνιών, οποίος αποτελείται από δυο λυχνίες ακτίνων Χ και δυο ανιχνευτές. Οι δύο λυχνίες μπορούν να λειτουργήσουν σε διαφορετικά kV ανεξάρτητα η μία από την άλλη, λαμβάνοντας δύο σειρές δεδομένων διαφορετικών ενεργειών ταυτόχρονα. Όταν ο υπολογιστικός τομογράφος δυο λυχνιών χρησιμοποιείται για λήψη εικόνων διπλής ενέργειας, η μια λυχνία λειτουργεί στα 80 kV και η άλλη στα 140 kV. Σε αυτή τη μελέτη εξετάστηκε η συμπεριφορά σε δύο ενέργειες μέσω μια σειράς πειραμάτων, υλικών όπως, πολυμερών ισοδύναμων με μαλακούς ιστούς και οστό, καθώς επίσης, συγκεντρώσεων ιωδίου και ασβεστίου. Χρησιμοποιήθηκαν δυο πρωτόκολλα λήψεων, ένα μιας ενέργειας με λήψεις στα 80, 100, 120, και 140 kV, καθώς και ένα πρωτόκολλο διπλής ενέργειας. Στα πειράματα που πραγματοποιήθηκαν μετρήθηκαν οι αριθμοί CT των υλικών, ο θόρυβος, η αντίθεση και ο λόγος αντίθεσης προς θόρυβο. Επίσης έγινε σύγκριση ως προς τα παραπάνω χαρακτηριστικά ποιότητα εικόνας με βάση τους παραπάνω δείκτες μεταξύ της συμβατικής 120 kV εικόνας και της ανακατασκευασμένης διπλής ενέργειας “virtual 120” kV. Η λεγόμενη “virtual 120” kV, μια αναμεμιγμένη εικόνα, κατασκευασμένη από δυο σειρές δεδομένων διαφορετικών ενεργειών, με γραμμικό συνδυασμό . Επιπλέον διερευνήθηκαν και συγκρίθηκαν ως προς τη ποιότητα εικόνας όλοι οι πιθανοί συνδυασμοί των δυο σειρών δεδομένων ενέργειας. Τα αποτελέσματα έδειξαν ότι μόνο υλικά υψηλού ενεργού ατομικού αριθμού, όπως το οστό και οι υψηλές συγκεντρώσεις ιωδίου 17, 25 και 35 mg/ml, καθώς και ασβεστίου 200, 250 και 300 mg/ml, είχαν ενισχυμένη αντίθεση στα 80 kV. Αξίζει να σημειωθεί ότι για μικρές συγκεντρώσεις ,όπως 1.25, 2.5, 3.5 mg/ml και 45, 83 mg/ml ιωδίου και ασβεστίου αντιστοίχως, η αντίθεση έχει συμπεριφορά μαλακού ιστού. Αντίθετα η τιμή του λόγου αντίθεσης προς θόρυβο δεν είναι όσο υψηλή είναι η τιμή της αντίθεσης. Τα επίπεδα θορύβου της εικόνας στα 80 kV είναι τόσο υψηλά, με αποτέλεσμα οι τιμές του λόγου αντίθεσης προς θόρυβο για όλα τα υλικά υψηλού ατομικού αριθμού να είναι χαμηλότερες στα 80 kV, συγκρινόμενες με τις αντίστοιχες τιμές στις υπόλοιπες τάσεις, παρά το γεγονός ότι η τιμή της αντίθεσης είναι πολύ υψηλή στα 80 kV. Όσο αναφορά τη σύγκριση της 120 kV εικόνας με την λεγόμενη “virtual 120” kV, τα αποτελέσματα των πειραμάτων έδειξαν ότι οι τιμές αντίθεσης του οστού, καθώς επίσης και των συγκεντρώσεων ιωδίου και ασβεστίου, ήταν ισοδύναμες, αλλά η τιμή του λόγου αντίθεσης προς θόρυβο της “virtual 120” kV εικόνας ήταν αρκετά χαμηλότερη σε σχέση με την 120 kV εικόνα. Τέλος το τρίτο πείραμα έδειξε ότι η τιμή της αντίθεσης αυξάνεται όσο αυξάνεται το ποσοστό της 80 kV πληροφορίας στη μεικτή εικόνα, ενώ ο λόγος αντίθεσης προς θόρυβο έχει ένα εύρος συνδυασμών που είναι υψηλός. Συγκεκραμένα οι γραμμικοί συνδυασμοί οι όποιοι είχαν τη μεγαλύτερη τιμή αντιθέσεις προς θόρυβο ήταν οι συντελεστές της 80 kV πληροφορίας από 0.4 έως 0.7. / Dual Energy Computed Tomography (DECT) is an evolving technique, which enhances material differentiation benefiting from the spectral properties of the materials. Spectral CT imaging requires the use of two different energy spectra, and it can distinguish elements, which differ considerably in atomic number. Therefore iodine (Z=53) which is used as contrast agent in CT scans, bone and plaque calcifications which contain calcium (Z=20), can be distinguished from other elements of which the human body consists, such as hydrogen (Z=1), oxygen (Z=8), carbon (Z=6) and nitrogen (Z=7), which are low atomic number elements. Currently there are three technical approaches of dual energy computed tomography. The dual layer detector system, which uses a single x-ray source and a detector with two scintillation layers one on top of one another. The top layer absorbs most of the low energy photons, while the bottom one the remaining high energy photons, acquiring two energy datasets simultaneously. The second technology of dual energy imaging is via fast kVp switching, which acquires two different energy spectra, alternating on a view by view basis between low and high kVp in a single rotation. Finally the third dual energy imaging technique, used in this study, is via the dual source CT system, which contains two x-ray tubes and two detectors. The two tubes can be operated independently at different kV. The dual source CT when it is used for dual energy scan is operated 80 kV/140 kV. Thus two dual energy datasets are acquired simultaneously. In this study the dual energy behavior of soft tissue equivalent materials, bone, iodine and calcium water solutions are examined through a series of experiments. Two acquisition protocols are used, a single energy at 80, 100, 120 and 140 kV, and a dual energy protocol. The CT numbers of these materials, as well as image noise, contrast and contrast to noise ratio are measured. Moreover comparison of these image quality features for standard single energy 120 kV image, which is the convention CT scan, and the “virtual 120” kV image is presented. The “virtual 120” kV is a blended image, reconstructed by the two dual energy datasets in a linear combination of In addition examination of all the possible linear combinations of the two dual energy datasets, and comparison in image quality, is presented. The results showed that only high Zeff materials had enhanced contrast at 80 kV, like bone, and the high iodine and calcium concentrations, such as 17, 25, and 35 mg/ml and 200, 250, and 300 mg/ml respectively. It is noteworthy that for small concentrations, such as 1.25, 2.5, 3.5 mg/ml and 45, 83 mg/ml of iodine and calcium respectively, contrast behavior is like the one of a soft tissue. Contrarily contrast to noise ratio is not as high as contrast at 80 kV. Image noise values at 80 kV are so high that CNR values for all high atomic number materials are lower at 80 kV compared to the ones of other voltages, despite the fact that contrast is very high at 80 kV. As it concerns the comparison of the single energy 120 kV image and the “virtual 120” kV, the results of the experiments showed that contrast values of bone, iodine and calcium concentrations, were equal, but contrast to noise ratio of the “virtual 120” was quite lower compared to the single energy 120 kV. Finally the third experiment showed that contrast values increase as the percentage of the 80 kV datasets increases in the blended image, while contrast to noise ratio has a range in which is higher. Specifically the linear combinations which had the highest CNR values were the ones with weighting factor of the 80 kV starting from 0.4 to 0.7.

Digital breast tomosynthesis (DBT) is a new technology for breast cancer screening that promises to complement mammography or supersede it to become the standard for breast imaging. DBT involves taking multiple images in order to synthesize a new image that represents a slice through the breast volume -- hence the term tomosynthesis. The primary advantage of this paradigm is that it can reduce the amount of overlapping anatomy in the data, leading to improved visualization of potentially-cancerous findings. The difficulty in DBT is quantifying the advantages of the technology and determining the optimal conditions for its clinical use. This dissertation describes a virtual trial framework for assessing and optimizing DBT technology for the specific task of detecting small, low-contrast masses in the breast. It addresses each component of the imaging chain to some degree, from the patients/phantoms to the imaging hardware to the model observers used to measure signal detectability. The main focus, however, is on quantifying tradeoffs between three key parameters that affect image quality: (1) scan angle, (2) number of projections, and (3) exposure. We show that in low-density breast phantoms, detectability generally increases with both scan angle and number of projections in the anatomical-variability-limited (high-exposure) regime. We also investigate how breast density affects the optimal DBT scan parameters. We show task-specific results that support using an adaptive paradigm in DBT, where the imaging system reconfigures itself in response to information about the patient's breast density. The virtual framework described in this dissertation provides a platform for further investigations of image quality in 3D breast imaging.

Computational tools of use in the objective assessment of image quality for tomography systems were developed for computer processing units (CPU) and graphics processing units (GPU) in the image quality lab at the University of Arizona. Fast analytic x-ray projection code called IQCT was created to compute the mean projection image for cone beam multi-slice helical computed tomography (CT) scanners. IQCT was optimized to take advantage of the massively parallel architecture of GPUs. CPU code for computing single photon emission computed tomography (SPECT) projection images was written calling upon previous research in the image quality lab. IQCT and the SPECT modeling code were used to simulate data for multimodality SPECT/CT observer studies. The purpose of these observer studies was to assess the benefit in image quality of using attenuation information from a CT measurement in myocardial SPECT imaging. The observer chosen for these studies was the scanning linear observer. The tasks for the observer were localization of a signal and estimation of the signal radius. For the localization study, area under the localization receiver operating characteristic curve (A(LROC)) was computed as A(LROC)^Meas = 0.89332 ± 0.00474 and A(LROC)^No = 0.89408 ± 0.00475, where "Meas" implies the use of attenuation information from the CT measurement, and "No" indicates the absence of attenuation information. For the estimation study, area under the estimation receiver operating characteristic curve (A(EROC)) was quantified as A(EROC)^Meas = 0.55926 ± 0.00731 and A(EROC)^No = 0.56167 ± 0.00731. Based on these results, it was concluded that the use of CT information did not improve the scanning linear observer's ability to perform the stated myocardial SPECT tasks. The risk to the patient of the CT measurement was quantified in terms of excess effective dose as 2.37 mSv for males and 3.38 mSv for females.Another image quality tool generated within this body of work was a singular value decomposition (SVD) algorithm to reduce the dimension of the eigenvalue problem for tomography systems with rotational symmetry. Agreement in the results of this reduced dimension SVD algorithm and those of a standard SVD algorithm are shown for a toy problem. The use of SVD toward image quality metrics such as the measurement and null space are also presented.

Optimization algorithms were developed for use with the Adaptive Joint Time-Frequency (AJFT) algorithm to reduce Inverse Synthetic Aperture Radar (ISAR) image blurring caused by higher-order target motion. A specific optimization was then applied to 3D motion detection. Evolutionary search methods based on the Genetic Algorithm (GA) and the Particle Swarm Optimization (PSO) algorithm were designed to rapidly traverse the solution space in order to find the parameters that would bring the ISAR image into focus in the cross-range. 3D motion detection was achieved by using the AJTF PSO to extract the phases of 3 different point scatterers in the target data and measuring their linearity when compared to an ideal phase for the imaging interval under investigation. The algorithms were tested against both simulated and real ISAR data sets.

BAKGRUND: En datortomograf (DT) är uppbyggd av ett röntgenrör och flertalet detektorer, röntgenröret sänder ut joniserande strålning. Barn som utsätts för joniserande strålning under en datortomografiundersökning har en förhöjd risk för strålningsinducerad cancer under en livstid. Det är nödvändigt för röntgensjuksköterskan att ha god kännedom om åtgärder som kan reducera stråldos utan att riskera bildkvaliteten.  SYFTE: Syftet med litteraturstudien var att beskriva åtgärder för att reducera stråldos med diagnostiskt accepterad bildkvalitet för barn som genomgår datortomografiundersökning.  METOD: Nio kvantitativa studier inkluderades i litteraturstudien. Studierna kvalitetsgranskades och resultaten sammanställdes enligt en modell av Friberg. Databaser som användes för sökningen var Pubmed och Scopus.  RESULTAT: Iterativa rekonstruktioner upprätthåller övergripande bildkvalitet utan att full dos används. En väl avvägd positionering och centring samt automatisk exponeringskontroll, minskning av kilovolt och milliampere*sekunder kan reducera stråldosen till barnet med diagnostisk accepterad bildkvalitet. Åtgärderna i relation med varandra påverkar bildkvaliteten och stråldosen.  KONKLUSION: Röntgensjuksköterskan kan reducera stråldosen till barnet och bidra till minskad risk för strålinducerad cancer. Att ändra parametrarna påverkar bildkvaliteten vilket gör att detta ej kan göras oaktsamt.

As there is a rapid growth in the field of wireless communications, the demand for various multimedia services is also increasing. The data that is being transmitted suffers from distortions through source encoding and transmission over errorprone channels. Due to these errors, the quality of the content is degraded. There is a need for service providers to provide certain Quality of Experience (QoE) to the end user. Several methods are being developed by network providers for better QoE.The human tendency mainly focuses on distortions in the Region of Interest(ROI) which are perceived to be more annoying compared to the Background(BG). With this as a base, the main aim of this thesis is to get an accurate prediction quality metric to measure the quality of the image over ROI and the BG independently. Reduced Reference Image Quality Assessment (RRIQA), a reduced reference image quality assessment metric, is chosen for this purpose. In this method, only partial information about the reference image is available to assess the quality. The quality metric is measured independently over ROI and BG. Finally the metric estimated over ROI and BG are pooled together to get aROI aware metric to predict the Mean Opinion Score (MOS) of the image.In this thesis, an ROI aware quality metric is used to measure the quality of distorted images that are generated using a wireless channel. The MOS of distorted images are obtained. Finally, the obtained MOS are validated with the MOS obtained from a database [1].It is observed that the proposed image quality assessment method provides better results compared to the traditional approach. It also gives a better performance over a wide variety of distortions. The obtained results show that the impairments in ROI are perceived to be more annoying when compared to the BG.

Approved for public release, distribution is unlimited / This thesis assesses the performance of the Naval Postgraduate School Aerosol Optical Depth (NPS AOD) model utilizing very high spatial resolution QuickBird (QB) satellite data. QuickBird derived AOD results are compared to other satellite and ground based AOD results, specifically, AErosol RObotic NETwork (AERONET), MODerate resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging SpectroRadiometer (MISR), and Advanced Very High Resolution Radiometer (AVHRR). Data is collected around Sir Bu Nuair Island, United Arab Emirates in September 2004 as part of the UAE2 Campaign. Satellite measured radiances are calibrated and due to spatial resolution differences between sensors, modal radiances are calculated for areas matching the highest resolution sensor. The AOD model is based on AVHRR wavelengths; hence, the modal satellite measured radiances are linearly extrapolated to the effective wavelengths of AVHRR. Results show application of the NPS AOD model to QuickBird data yields findings that are consistent with other satellite and ground based retrievals. In general, the NPS AOD model works well for nadir and near-nadir view angles, but not for high zenith angles. / Lieutenant Commander, United States Navy