Fusing spatial and temporal components for real-time depth data enhancement of dynamic scenes

The depth images from consumer depth cameras (e.g., structured-light/ToF devices) exhibit a substantial amount of artifacts (e.g., holes, flickering, ghosting) that needs to be removed for real-world applications. Existing methods cannot entirely remove them and perform slow. This thesis proposes a new real-time spatio-temporal depth image enhancement filter that completely removes flickering and ghosting, and significantly reduces holes. This thesis also presents a novel depth-data capture setup and two data reduction methods to optimize the performance of the proposed enhancement method

Development of whole-heart myocardial perfusion magnetic resonance imaging

Myocardial perfusion imaging is of huge importance for the detection of coronary artery disease (CAD), one of the leading causes of morbidity and mortality worldwide, as it can provide non-invasive detection at the early stages of the disease. Magnetic resonance imaging (MRI) can assess myocardial perfusion by capturing the rst-pass perfusion (FPP) of a gadolinium-based contrast agent (GBCA), which is now a well-established technique and compares well with other modalities. However, current MRI methods are restricted by their limited coverage of the left ventricle. Interest has therefore grown in 3D volumetric \whole-heart" FPP by MRI, although many challenges currently limit this. For this thesis, myocardial perfusion assessment in general, and 3D whole-heart FPP in particular, were reviewed in depth, alongside MRI techniques important for achieving 3D FPP. From this, a 3D `stack-of-stars' (SOS) FPP sequence was developed with the aim of addressing some current limitations. These included the breath-hold requirement during GBCA rst-pass, long 3D shot durations corrupted by cardiac motion, and a propensity for artefacts in FPP. Parallel imaging and compressed sensing were investigated for accelerating whole-heart FPP, with modi cations presented to potentially improve robustness to free-breathing. Novel sequences were developed that were capable of individually improving some current sequence limits, including spatial resolution and signal-to-noise ratio, although with some sacri ces. A nal 3D SOS FPP technique was developed and tested at stress during free-breathing examinations of CAD patients and healthy volunteers. This enabled the rst known detection of an inducible perfusion defect with a free-breathing, compressed sensing, 3D FPP sequence; however, further investigation into the diagnostic performance is required. Simulations were performed to analyse potential artefacts in 3D FPP, as well as to examine ways towards further optimisation of 3D SOS FPP. The nal chapter discusses some limitations of the work and proposes opportunities for further investigation.Open Acces

Single-shot spectroscopy of solid-state photoinduced dynamics far from equilibrium

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 245-252).Ultrafast single-shot spectroscopy was developed and improved as a method to observe photoinduced dynamics far from equilibrium. The method was then employed to illuminate material dynamics in platinum-halide quasi-one-dimensional chain compounds (PtI) and in the semimetal bismuth. Both material systems exhibit strongly coupled energetic modes; as a result, their study under laser pulse excitation offers the opportunity to explore the same processes that underlie their unique properties. Our measurements have pushed the photoinduced study of these materials to new extremes toward a better understanding of material response and control far from equilibrium. In this thesis, the single-shot method is introduced and analyzed, and measurements on PtI and bismuth are presented and discussed. Collectively, the measurements offer a view into how materials with strong electron-phonon coupling respond to photoexcitation across dimension, timescale, and excitation density. Dimensionality is explored qualitatively between the PtI chain sample and bismuth samples of varying thickness. The time evolution upon laser excitation is monitored from the instantaneous response out to several hundred picoseconds. The photoexcitation itself is varied from weak (corresponding to most published literature on both materials) to very strong (exceeding the thresholds for visualizing dynamics with conventional methods). We describe our results in the context of material dynamics on the microscale and propose future directions. New dynamics were observed in PtI chains that suggest long-lived structural and electronic states under high irradiation. The possibility of collective structural rearrangement with a long lifetime is proposed. In bismuth, high photoexcitation measurements traversed the material's potential energy surface along the coordinate of structural distortion. We report control of the excitation-dependent photoinduced phase by dimensional constraint, as well as ballistic transport effects that govern this interplay. This research enables future advancements on two fronts. The instrumental developments enable visualization of irreversible events for a wider range of materials. The physical insights gained for the materials studied here characterize key processes pertinent to technological applications and off insights that may govern behavior far from equilibrium for broader classes of materials.by Johanna Wendlandt Wolfson.Ph.D

A Unified Cognitive Model of Visual Filling-In Based on an Emergic Network Architecture

The Emergic Cognitive Model (ECM) is a unified computational model of visual filling-in based on the Emergic Network architecture. The Emergic Network was designed to help realize systems undergoing continuous change. In this thesis, eight different filling-in phenomena are demonstrated under a regime of continuous eye movement (and under static eye conditions as well). ECM indirectly demonstrates the power of unification inherent with Emergic Networks when cognition is decomposed according to finer-grained functions supporting change. These can interact to raise additional emergent behaviours via cognitive re-use, hence the Emergic prefix throughout. Nevertheless, the model is robust and parameter free. Differential re-use occurs in the nature of model interaction with a particular testing paradigm. ECM has a novel decomposition due to the requirements of handling motion and of supporting unified modelling via finer functional grains. The breadth of phenomenal behaviour covered is largely to lend credence to our novel decomposition. The Emergic Network architecture is a hybrid between classical connectionism and classical computationalism that facilitates the construction of unified cognitive models. It helps cutting up of functionalism into finer-grains distributed over space (by harnessing massive recurrence) and over time (by harnessing continuous change), yet simplifies by using standard computer code to focus on the interaction of information flows. Thus while the structure of the network looks neurocentric, the dynamics are best understood in flowcentric terms. Surprisingly, dynamic system analysis (as usually understood) is not involved. An Emergic Network is engineered much like straightforward software or hardware systems that deal with continuously varying inputs. Ultimately, this thesis addresses the problem of reduction and induction over complex systems, and the Emergic Network architecture is merely a tool to assist in this epistemic endeavour. ECM is strictly a sensory model and apart from perception, yet it is informed by phenomenology. It addresses the attribution problem of how much of a phenomenon is best explained at a sensory level of analysis, rather than at a perceptual one. As the causal information flows are stable under eye movement, we hypothesize that they are the locus of consciousness, howsoever it is ultimately realized

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Μέτρηση αιμοδυναμικών χαρακτηριστικών με απεικόνιση μαγνητικού συντονισμού

Στο ΚΕΦΑΛΑΙΟ 1 παρουσιάζονται οι πιο βασικές αρχές της ρευστοδυναμικής. Αναφέρονται οι εξισώσεις Navier- Stokes οι οποίες με την εξίσωση του συνεχούς της μάζας και με συνθήκες περιορισμού, οδηγούν στο φορμαλισμό της ροής. Αυτές οι εξισώσεις και τα χαρακτηριστικά ροής, όπως η διατμητική τάση των αγγειακών τοιχωμάτων, θα αποτελέσουν το αντικείμενο διερεύνησης. Το ΚΕΦΑΛΑΙΟ 2 αναφέρεται περιγραφικά στη τεχνική της Μαγνητικής Αγγειογραφίας, στην οποία βασίζονται οι λήψεις όλων των δεδομένων στη ν εργασία αυτή. Το ΚΕΦΑΛΑΙΟ 3 παρουσιάζει τα υλικά και τη μέθοδο που ακολουθήθηκαν για τον υπολογισμό του WSS. Το ΚΕΦΑΛΙΑΟ 4 παρουσιάζει τα υλικά και τη μέθοδο για τον υπολογισμό των θεμελιωδών χαρακτηριστικών της αιματικής ροής σε συνθήκες εργαστήριου. Στα ΚΕΦΑΛΑΙΑ 5 και 6 παρουσιάζονται όλα τα αποτελέσματα και από τα δυο μέρη (in vivo και in-vitro) υπό τη μορφή πινάκων και γραφημάτων. Το ΚΕΦΑΛΑΙΟ 7 χωρίζεται στο τμήμα Ι και ΙΙ τα οποία γίνεται η ανάλυση και ο σχολιασμός των αποτελεσμάτων που παρουσιάστηκαν στα κεφαλαία 5 (Ι) και 6 (ΙΙ) αντίστοιχα. Το ΚΕΦΑΛΑΙΟ 8 οδηγεί τον αναγνώστη στο σύνολο των συμπερασμάτων και τη συσχέτιση τους με την κλινική πράξη. Η διατριβή ολοκληρώνεται με τους περιορισμούς που αναπόφευκτα παρουσιάζονταιIn CHAPTER 1, the reader is introduced the fundamental fluid dynamics principles including the Navier- Stokes set of equations, which together with the mass conservation equation, and following the imposed boundary conditions, they give rise –the Poiseuille’s Law of fluid CHAPTER 2 deals with Magnetic Resonance Angiography and its applications to the human circulatory system. CHAPTER 3 presents the materials and method that were followed in order to calculate WSS equations in clinical practice CHAPTER 4 in a similar way describes the IN-VITRO set up and instrumentation that was used in order to simulate blood flow. CHAPTERS 5 and 6 display all the acquired data from the in-vivo and in-vitro set ups. CHAPTER 7 is divided into two sections. The first refers to the analysis and discussion of the in vivo results and the second refers to the analysis and discussion of the in-vitro results . CHAPTER 8 takes the reader to the sum of all the conclusions. The thesis concludes with a brief presentation of the inevitable limitations of the work and finally with a complete proposal for future works that can bring the study of hemodynamic parameters using MRA to a new era