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<p>Vocal fold vibration results in voice production. Optimal hydration levels contribute to self-sustained vocal fold vibration and preservation of voice quality. Adequate hydration is implicated as a factor in maintaining voice and preventing voice problems. Voice problems affect up to one third of adults during their lifetime. But whether altered hydration state adversely affects vocal fold biology and biomechanics is still unclear. To untangle the effects of systemic dehydration on vocal fold biology, we developed a water restriction protocol on lab animals that can translate to humans. Our results showed that dehydration induced by restricted water access downregulated the gene expression of IL-1α and desmoglein-1, upregulated the gene expression level of hyaluronidase-2, and downregulated hyaluronic acid (HA).</p> <p>Clinically, hydration treatments are hypothesized to maintain the viscoelastic properties of vocal folds. However, our understanding of the relationship between vocal fold tissue hydration level and biomechanical properties is still evolving. To investigate the effects of dehydration on biomechanical properties we used an ex vivo experimental design. We hypothesized that the optimal stiffness of vocal folds would be impacted after dehydration via losing both water and HA, but that the stiffness properties would recover through rehydration. To test this hypothesis, we experimentally treated porcine vocal fold samples using two different approaches: 1) immersion in hypertonic solution (15% NaCl in ddH2O) and PBS sequentially to mimic dehydration and rehydration, and 2) incubation with hyaluronidase (Hyal) to mimic HA loss during dehydration. Our results showed that loss of water increased tissue stiffness and could be recovered through rehydration in a certain degree. In addition, loss of HA increased tissue stiffness. </p> <p>In While dehydration decreases total body blood volume, different tissues and organs of the body may be impacted in different ways from dehydration. Therefore, it is important to investigate the hemodynamic alterations during changes to hydration status. Magnetic resonance angiography (MRA) and ultrasound imaging were employed to identify the delicate vascular geometry and hemodynamics of the laryngeal blood supply. Animals underwent both MRA and ultrasound imaging at baseline, dehydration and rehydration time points. Our results showed that dehydration impacted the blood supply to larynx. This blood supply was restored through rehydration treatment.</p> <p>Overall, this research has been successful in establishing a mild dehydration animal model, providing evidence from gene and protein levels that dehydration affects cytokine production and extracellular matrix components (ECM) in vocal fold, demonstrating the vocal fold tissue biomechanical behavior after dehydration and loss of HA, and offering a combination application of MRA and ultrasound imaging to study vascular geometry and hemodynamics of the blood supply to the vocal fold region.</p>

Heart disease is one of the primary causes of morbidity and mortality for the adult population over the age of 65. Furthermore, ailments such as hypertension can affect as many as 50% of the adult population over the age of 45. If left untreated, these ailments eventually precipitate the onset of diastolic dysfunction and heart failure. Diastolic dysfunction is the alteration or impairment of performance in either the left or right ventricle of the heart. Although there has been a marked increase in study of this disease, there is still an apparent difficulty to diagnose patients. Flow visualization techniques have been commonly employed to study the development of these diseases as they relate to the filling process of the ventricles. One method, Echo Particle Image Velocimetry (Echo-PIV) is a relatively new method for cardiac flow chamber visualization, with the potential to provide physicians with a cost-effective and safe method for obtaining high temporal resolution recordings for extending knowledge on the filling processes in cardiac chamber flow. This work presents a new approach to extending the capabilities of Echo-PIV for more accurate measurement of cardiac flows for patients with poor quality recordings. Currently, much of the literature notes that temporal resolution and poor acoustic windows results in exclusion from study. These recordings are more representative of the contrast-enhancement studies used by physicians to better identify chamber walls. When applying standard PIV cross-correlation techniques, measurements tend to fail due to image noise and artifacts. By implementing a Moving Ensemble (MWE) with Product of Correlation (PoC) processing scheme, measurement accuracy, reliability, and robustness can be obtained for measurement in left ventricular filling assessment. / Master of Science

Since early 1960s, ultrasound has become one of the most widely used medical imaging device as a diagnostic tool or an image guider for surgical intervention because of its high portability, non-ionization, non-invasiveness and low cost. Although continuous improvements in commercial equipments have been underway for many years, almost all systems are developed with pulse-echo geometry. In this research, a newly invented ultrasound sensor array was incorporated into the developments of a projection imaging system. Three C-scan prototypes, which included prototypes #1, #2 and an ultrasound mammography system, were constructed. Systematic and Evaluative studies included ultrasound CT, 3-D ultrasound, and multi-modality investigations were also performed. Furthermore, a new analytical method to model ultrasound forward scattering distribution (FSD) was developed by employing a specific annular apparatus. After applying this method, the scattering-corrected C-scan images revealed more detail structures as compared to unprocessed images. This new analytical modelling approach is believed to be effective for most imaging systems operating in projection geometry. In summary, while awaiting additional clinical validation, the C-scan ultrasound prototypes with the state-of-the-art PE-CMOS sensor arrays can provide veritable value and holds real and imminent promise in medical diagnostic imaging. Potential future uses of C-scan ultrasound include but not limit to computerized tomography, biopsy guidance, therapeutic device placing, foreign object detection, pediatric imaging, breast imaging, prostate imaging, human extremities imaging and live animal imaging. With continuous research and development, we believe that C-scan ultrasound has the potential to make a significant impact in the field of medical ultrasound imaging. / Ph. D.

Der zunehmende Einsatz regenerativer Energiequellen erfordert die Nutzung von Energiezwischenspeichern, die umweltfreundlich, günstig und skalierbar sein sollten. Die Zink-Luft-Flussbatterie (ZLFB) kann perspektivisch diese Anforderungen erfüllen, wobei zur Bereitstellung der gespeicherten Energie eine Suspension aus Zinkpartikeln in einem gelierten Elektrolyt durch eine elektrochemische Zelle gepumpt wird. Um die Strömungsstruktur der ZLFB auszulegen und Fehlfunktionen zu vermeiden, ist ein grundlegendes Verständnis der Rheologie der Zinksuspension notwendig. Außerdem kann über die Einstellung einer geeigneten Strömung die bei der Entladung erreichte elektrische Leistungsdichte gesteigert werden. Bereits die Flüssigphase der Zinksuspension weist eine komplexe nicht-Newtonsche Rheologie auf, welche durch die Zugabe der Partikel komplexer wird. Für das grundlegende Verständnis der Rheologie werden daher Modellexperimente durchgeführt, wobei in dieser Arbeit ein L-förmiger Kanal mit Strömungsaufweitung untersucht wurde, um die komplexen strömungsmechanischen Eigenschaften der Zinksuspension abzubilden. Zur Erfassung des Strömungsfeldes ist eine Ortsauflösung von 1 … 2 mm in einem Messbereich von 20 × 15 mm2 erforderlich. Ultraschall ist prinzipiell geeignet, um das Strömungsfeld in der opaken Suspension zu erfassen, wobei die wesentliche Herausforderung in den starken Wellenfrontverzerrungen besteht, welche durch die Zinkpartikel eingebracht werden. Es konnte gezeigt werden, dass die Ultrasound Imaging Velocimetry (UIV) robuster gegenüber diesen Störungen ist, als die Ultraschall-Doppler-Velozimetrie (UDV). Die UIV wurde daher mittels Geschwindigkeitsnormal an die messtechnischen Randbedingungen der Zinksuspension angepasst und charakterisiert. Bei einer Ortsauflösung von 1,6 mm wurde eine Gesamtmessunsicherheit von 2,5 % axial und 4,1 % lateral zur Schallausbreitungsrichtung erreicht. Das im Modellexperiment gemessene Strömungsfeld weist eine Totzone an der Strömungsumlenkung auf, deren Auftreten durch eine von der Scherhistorie abhängige Viskosität erklärt werden kann. Dieser Effekt wird als Thixotropie bezeichnet. Durch die In-situ-Messung der Strömung in einer aktiven ZLFB kann eine Korrelation von Strömung und elektrischer Leistung erfolgen und die erzielte Leistungsdichte perspektivisch durch eine Anpassung der Strömung gesteigert werden. Bei der Messung im 2,6 mm hohen Anodenspalt muss aufgrund der komplexen Rheologie der Suspension und der daraus resultierenden hohen Geschwindigkeitsgradienten eine Ortsauflösung von unter 100 µm bei gleichzeitig kleiner Ultraschallfrequenz realisiert werden, da der Ultraschall für hohe Frequenzen nicht in die Zinksuspension eindringt. Um dieses Ziel zu erreichen, wurde die Super Resolution Ultrasound Particle Tracking Velocimetry (SRPTV) genutzt, welche Ortsauflösungen unterhalb des Beugungslimits ermöglicht. Einzelne nichtlineare Streupartikel werden mittels Harmonic Imaging isoliert abgebildet und verfolgt, wobei die durch die Zinkpartikel eingebrachten Wellenfrontstörungen durch einen kohärenzgewichteten Strahlformer kompensiert werden. Es wurde eine Ortsauflösung von 67 µm axial und 30 µm lateral zur Schallausbreitungsrichtung bei einer Anregungswellenlänge von 330 µm erreicht. Trotz der stark streuenden Zinksuspension, konnte so eine Messung in der aktiven ZLFB mit einer maximalen Messunsicherheit von 12,5 % durchgeführt werden. Dabei wurde eine Wandgleitgeschwindigkeit von 3 mm s−1 bei einer maximalen Geschwindigkeit von etwa 8 mm s−1 festgestellt. Die SRPTV kann darüber hinaus in anderen technischen Prozessen eingesetzt werden, in denen Suspensionsströmungen in kleinen Geometrien auftreten.:Symbolverzeichnis xiii Abkürzungsverzeichnis xv 1 Einleitung 1 1.1 Motivation und Zielstellung 1 1.2 Stand der Technik 4 1.3 Lösungsansatz und Struktur der Arbeit 8 2 Theoretische Grundlagen 11 2.1 Grundlagen der Schallausbreitung 11 2.1.1 Schallausbreitung in homogenen Medien 11 2.1.2 Schallausbreitung in inhomogenen Medien 13 2.2 Ultraschall Bildgebung 14 2.2.1 Phased-Array-Prinzip 15 2.2.2 Plane wave imaging 16 2.2.3 Grenzen der Schallfeldfokussierung 16 2.3 Messung von Strömungsfeldern 17 2.3.1 Ultraschall-Doppler-Velozimetrie 18 2.3.2 Ultrasound Imaging Velocimetry 19 2.3.3 Ultrasound Particle Tracking Velocimetry 19 2.4 Nichtlineare akustische Effekte 20 2.4.1 Beschreibung von Linearität 20 2.4.2 Interaktion von nichtlinearen Streupartikeln und Schallwelle 20 2.4.3 Harmonic Imaging 21 3 Experimentelle Grundlagen 25 3.1 Charakterisierung der Zinksuspension 25 3.1.1 Zusammensetzung der Zinksuspension 25 3.1.2 Bestimmung von Dämpfung und Schallgeschwindigkeit 26 3.1.3 Bestimmung der spezifischen akustischen Impedanz 29 3.2 Messtechnik 30 3.2.1 Ultraschallforschungsplattform: Phased Array Ultrasound Dopp- ler Velocimeter 30 3.2.2 Ultraschallwandler 32 4 Verfahren zur Strömungsmessung im Modellexperiment 37 4.1 Experimenteller Aufbau 37 4.2 Untersuchung geeigneter Verfahren zur Messung von Strömungsfel- dern in der Zinksuspension 38 4.3 Optimierung der Signalverarbeitung und Charakterisierung der Messei- genschaften 44 4.3.1 Geschwindigkeitsnormal 44 4.3.2 Optimierung der Messsystemparameter 45 4.3.3 Charakterisierung der Messeigenschaften 48 4.3.4 Validierung 49 4.4 Messung der Suspensionsströmung im Modellexperiment 55 4.4.1 Messergebnisse 55 4.4.2 Vergleich von Simulation und Messung 58 4.5 Fazit 61 5 Verfahren zur In-situ-Strömungsmessung in einer Zink-Luft-Flussbatterie 63 5.1 Experimenteller Aufbau 63 5.2 Strömungsmessung unterhalb des Beugungslimits - Super Resolution Ultrasound Particle Tracking Velocimetry (SRPTV) 65 5.2.1 Nutzung nichtlinearer Streupartikel 68 5.2.2 Trennung von linearem und nichtlinearem Signalanteil 72 5.2.3 Strahlformung mit Kompensation der Streuung 76 5.2.4 Particle Tracking 80 5.3 Charakterisierung der Messeigenschaften 81 5.3.1 Vorgehen zur Charakterisierung der Messeigenschaften 82 5.3.2 Untersuchung der Positionsunsicherheit 83 5.3.3 Untersuchung der Geschwindigkeitsunsicherheit 92 5.4 Messung an einer aktiven Zink-Luft-Flussbatterie 95 5.4.1 Aufbau und Durchführung 95 5.4.2 Messergebnisse 97 5.4.3 Vergleich von Simulation und Messung 97 5.5 Fazit 102 6 Zusammenfassung und Ausblick 103 6.1 Erkenntnisse und Fortschritt 103 6.1.1 Ultrasound Imaging Velocimetry 103 6.1.2 Super Resolution Ultrasound Particle Tracking Velocimetry 104 6.1.3 Fazit 106 6.2 Ausblick und weiterführende Arbeiten 106 6.2.1 Messtechnik 106 6.2.2 Anwendung 107 Literaturverzeichnis 109 Publikationsverzeichnis 117 Artikel in Zeitschriften mit peer-review 117 Tagungsbeiträge 117 Patente 119 / For the efficient use of renewable energies, energy storage systems are required that are environmentally friendly, low priced and scalable. The zinc-air flow battery (ZAB), which is operated by pumping an opaque suspension of zinc particles in an gelled electrolyte through an electrochemical cell, is a promising candidate as energy storage system for these requirements. To design the fluidic structures and avoid malfunction, a fundamental understanding of the rheology of the zinc suspension is required. Additionally, the electrical performance of the cell can be imporved by optimizing the flow in the electrochemical cell. The liquid phase of the suspension itself has complex non-Newtonian properties, which are even more complex when the particles are considered. For the fundamental understanding of the suspension rheology, model experiments are conducted. In this work an L-shaped channel with a widening is used to represent relevant effects from the complex rheology of the suspension. To measure the flow field, a spatial resolution of 1 … 2 mm and a measurement area of 20 × 15 mm2 are required. Ultrasound can be used to measure the flow in opaque liquids, but wavefront distortions are introduced by the zinc particles. Established measurement methods for homogeneous opaque fluids, the Ultrasound Imaging Velocimetry (UIV) and the Ultrasound Doppler Velocimetry (UDV), were compared for the application at the suspension. The UIV has a 50 % lower random deviation, which makes it more suitable for the flow measurement in the suspension and it was adapted to the measurement conditions in the suspension. At a spatial resolution of 1.66 mm, a velocity uncertainty of 2.5 % axial and 4.1 % lateral to the ultrasound propagation were achieved. The application of the UIV to the suspension flow in the model experiment revealed a thixotropic behavior of the fluid, which resulted in a dead flow zone opposite to the inlet of the channel. The in situ measurement of the flow in an active ZAB, allows to correlate electrical performance and flow and thereby an improvement of the cell performance by adapting the flow. For the measurement in the anodic channel with a width of 2.6 mm, a spatial resolution of 100 µm is required because of the high velocity gradients due to the non-Newtonian rheology of the suspension. The high spatial resolution has to be achieved at low ultrasound frequencies, since the ultrasound does not penetrate into the suspension for high frequencies. To achieve this, the Super Resolution Ultrasound Particle Tracking Velocimetry (SRPTV) was used, which allows a spatial resolution beyond the diffraction limit. Harmonic Imaging is used to image isolated non-linear tracer particles, which are tracked for velocity estimation. The speckle and image distortion due to the induced wavefront distortions are compensated with a coherence weighting beamformer. A spatial resolution of 67 µm axial and 30 µm lateral to the ultrasound propagation were achieved. Despite the strong scattering of the ultrasound at the zinc particles, a maximum velocity uncertainty of 12.5 % referred to the maximum velocity was achieved for the measurement in the active ZAB. A slip velocity of 3 mm at a maximum velocity of 8 mm was observed. The SRPTV can be applied to other technical processes, where suspension flows in small geometries play an important role.:Symbolverzeichnis xiii Abkürzungsverzeichnis xv 1 Einleitung 1 1.1 Motivation und Zielstellung 1 1.2 Stand der Technik 4 1.3 Lösungsansatz und Struktur der Arbeit 8 2 Theoretische Grundlagen 11 2.1 Grundlagen der Schallausbreitung 11 2.1.1 Schallausbreitung in homogenen Medien 11 2.1.2 Schallausbreitung in inhomogenen Medien 13 2.2 Ultraschall Bildgebung 14 2.2.1 Phased-Array-Prinzip 15 2.2.2 Plane wave imaging 16 2.2.3 Grenzen der Schallfeldfokussierung 16 2.3 Messung von Strömungsfeldern 17 2.3.1 Ultraschall-Doppler-Velozimetrie 18 2.3.2 Ultrasound Imaging Velocimetry 19 2.3.3 Ultrasound Particle Tracking Velocimetry 19 2.4 Nichtlineare akustische Effekte 20 2.4.1 Beschreibung von Linearität 20 2.4.2 Interaktion von nichtlinearen Streupartikeln und Schallwelle 20 2.4.3 Harmonic Imaging 21 3 Experimentelle Grundlagen 25 3.1 Charakterisierung der Zinksuspension 25 3.1.1 Zusammensetzung der Zinksuspension 25 3.1.2 Bestimmung von Dämpfung und Schallgeschwindigkeit 26 3.1.3 Bestimmung der spezifischen akustischen Impedanz 29 3.2 Messtechnik 30 3.2.1 Ultraschallforschungsplattform: Phased Array Ultrasound Dopp- ler Velocimeter 30 3.2.2 Ultraschallwandler 32 4 Verfahren zur Strömungsmessung im Modellexperiment 37 4.1 Experimenteller Aufbau 37 4.2 Untersuchung geeigneter Verfahren zur Messung von Strömungsfel- dern in der Zinksuspension 38 4.3 Optimierung der Signalverarbeitung und Charakterisierung der Messei- genschaften 44 4.3.1 Geschwindigkeitsnormal 44 4.3.2 Optimierung der Messsystemparameter 45 4.3.3 Charakterisierung der Messeigenschaften 48 4.3.4 Validierung 49 4.4 Messung der Suspensionsströmung im Modellexperiment 55 4.4.1 Messergebnisse 55 4.4.2 Vergleich von Simulation und Messung 58 4.5 Fazit 61 5 Verfahren zur In-situ-Strömungsmessung in einer Zink-Luft-Flussbatterie 63 5.1 Experimenteller Aufbau 63 5.2 Strömungsmessung unterhalb des Beugungslimits - Super Resolution Ultrasound Particle Tracking Velocimetry (SRPTV) 65 5.2.1 Nutzung nichtlinearer Streupartikel 68 5.2.2 Trennung von linearem und nichtlinearem Signalanteil 72 5.2.3 Strahlformung mit Kompensation der Streuung 76 5.2.4 Particle Tracking 80 5.3 Charakterisierung der Messeigenschaften 81 5.3.1 Vorgehen zur Charakterisierung der Messeigenschaften 82 5.3.2 Untersuchung der Positionsunsicherheit 83 5.3.3 Untersuchung der Geschwindigkeitsunsicherheit 92 5.4 Messung an einer aktiven Zink-Luft-Flussbatterie 95 5.4.1 Aufbau und Durchführung 95 5.4.2 Messergebnisse 97 5.4.3 Vergleich von Simulation und Messung 97 5.5 Fazit 102 6 Zusammenfassung und Ausblick 103 6.1 Erkenntnisse und Fortschritt 103 6.1.1 Ultrasound Imaging Velocimetry 103 6.1.2 Super Resolution Ultrasound Particle Tracking Velocimetry 104 6.1.3 Fazit 106 6.2 Ausblick und weiterführende Arbeiten 106 6.2.1 Messtechnik 106 6.2.2 Anwendung 107 Literaturverzeichnis 109 Publikationsverzeichnis 117 Artikel in Zeitschriften mit peer-review 117 Tagungsbeiträge 117 Patente 119

Humans make use of more than just the audio signal to perceive speech. Behavioral and neurological research has shown that a person's knowledge of how speech is produced influences what is perceived. With methods for collecting articulatory data becoming more ubiquitous, methods for extracting useful information are needed to make this data useful to speech scientists, and for speech technology applications. This dissertation presents feature extraction methods for ultrasound images of the tongue and for data collected with an Electro-Magnetic Articulograph (EMA). The usefulness of these features is tested in several phoneme classification tasks. Feature extraction methods for ultrasound tongue images presented here consist of automatically tracing the tongue surface contour using a modified Deep Belief Network (DBN) (Hinton et al. 2006), and methods inspired by research in face recognition which use the entire image. The tongue tracing method consists of training a DBN as an autoencoder on concatenated images and traces, and then retraining the first two layers to accept only the image at runtime. This 'translational' DBN (tDBN) method is shown to produce traces comparable to those made by human experts. An iterative bootstrapping procedure is presented for using the tDBN to assist a human expert in labeling a new data set. Tongue contour traces are compared with the Eigentongues method of (Hueber et al. 2007), and a Gabor Jet representation in a 6-class phoneme classification task using Support Vector Classifiers (SVC), with Gabor Jets performing the best. These SVC methods are compared to a tDBN classifier, which extracts features from raw images and classifies them with accuracy only slightly lower than the Gabor Jet SVC method.For EMA data, supervised binary SVC feature detectors are trained for each feature in three versions of Distinctive Feature Theory (DFT): Preliminaries (Jakobson et al. 1954), The Sound Pattern of English (Chomsky and Halle 1968), and Unified Feature Theory (Clements and Hume 1995). Each of these feature sets, together with a fourth unsupervised feature set learned using Independent Components Analysis (ICA), are compared on their usefulness in a 46-class phoneme recognition task. Phoneme recognition is performed using a linear-chain Conditional Random Field (CRF) (Lafferty et al. 2001), which takes advantage of the temporal nature of speech, by looking at observations adjacent in time. Results of the phoneme recognition task show that Unified Feature Theory performs slightly better than the other versions of DFT. Surprisingly, ICA actually performs worse than running the CRF on raw EMA data.

Although the drug-eluting stent (DES) has dramatically reduced the rate of coronary restenosis, it still occurs in up to 20% of patients with a DES. Monitoring drug delivery could be one way to decrease restenosis rates. We demonstrate real-time photoacoustic imaging and spectroscopy (PAIS) using a wavelength-tunable visible laser and clinical ultrasound scanner to track cardiac drug delivery. The photoacoustic signal was initially calibrated using porcine myocardial samples soaked with a known concentration of a drug surrogate (Dil). Next, an in situ coronary artery was perfused with DiI for 20 min and imaged to monitor dye transport in the tissue. Finally, a partially DiI-coated stent was inserted into the porcine brachiocephalic trunk for imaging. The photoacoustic signal was proportional to the DiI concentration between 2.4 and 120 mu g/ml, and the dye was detected over 1.5 mm from the targeted coronary vessel. Photoacoustic imaging was also able to differentiate the DiI-coated portion of the stent from the uncoated region. These results suggest that PAIS can track drug delivery to cardiac tissue and detect drugs loaded onto a stent with sub-mm precision. Future work using PAIS may help improve DES design and reduce the probability of restenosis. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

This dissertation presents a new 2D ultrasound-based visual servoing method. The main goal is to automatically guide a robotized 2D ultrasound probe held by a medical robot in order to reach a desired cross-section ultrasound image of an object of interest. This method allows to control both the in-plane and out-of-plane motions of a 2D ultrasound probe. It makes direct use of the 2D ultrasound image in the visual servo scheme, where the feed-back visual features are combinations of image moments. To build the servo scheme, we develop the analytical form of the interaction matrix that relates the image moments time variation to the probe velocity. That modeling is theoretically verified on simple shapes like spherical and cylindrical objects. In order to be able to automatically position the 2D ultrasound probe with respect to an observed object, we propose six relevant independent visual features to control the 6 degrees of freedom of the robotic system. Then, the system is endowed with the capability of automatically interacting with objects without any prior information about their shape, 3D parameters, nor 3D location. To do so, we develop on-line estimation methods that identify the parameters involved in the built visual servo scheme. We conducted both simulation and experimental trials respectively on simulated volumetric objects, and on both objects and soft tissues immersed in a water-filled tank. Successful results have been obtained, which show the validity of the developed methods and their robustness to different errors and perturbations especially those inherent to the ultrasound modality. Keywords: Medical robotics, visual servoing, 2D ultrasound imaging, kinematics modeling, model-free servoing.

Οι καρδιαγγειακές παθήσεις αποτελούν σήμερα την πρώτη αιτία θανάτου στις αναπτυγμένες χώρες. Οι αιτίες που τις προκαλούν συνδέονται πολύ συχνά με τις ιδιότητες και την γενική κατάσταση των τοιχωμάτων των μεγάλων αρτηριών. Η υπερηχητική απεικόνιση των τελευταίων είναι εξαιρετικά σημαντική για τη διάγνωση πιθανών παθολογικών καταστάσεων, καθώς χαρακτηρίζεται από χαμηλό κόστος και ελάχιστη επιβάρυνση για τον οργανισμό του ασθενούς, ενώ μπορεί να πραγματοποιείται σε πραγματικό χρόνο. Επιπλέον, οι υπερηχητικές τεχνικές απεικόνισης επιτρέπουν την παρακολούθηση της κίνησης των αρτηριακών τοιχωμάτων, από την οποία μπορούν να εξαχθούν αρκετά ασφαλή συμπεράσματα για την κατάστασή τους. Για την παρακολούθηση της κίνησης των αρτηριακών τοιχωμάτων έχουν χρησιμοποιηθεί διάφορες μέθοδοι, με κυριότερες αυτές που βασίζονται στο φαινόμενο Doppler (Tissue Doppler Imaging), τις διαφορικές μεθόδους οπτικής ροής και τις μεθόδους ταύτισης περιοχών (block matching). Οι μέθοδοι Doppler είναι εξαιρετικά ακριβείς, μόνο όμως κοντά στη διεύθυνση της υπερηχητικής δέσμης. Οι μέθοδοι οπτικής ροής μπορούν να χρησιμοποιηθούν σε διδιάστατες απεικονίσεις με αρκετά ικανοποιητική ακρίβεια, αδυνατούν ωστόσο να παρακολουθήσουν μεγάλες μετατοπίσεις. Από την άλλη πλευρά, οι μέθοδοι ταύτισης περιοχών δεν παρουσιάζουν τα παραπάνω προβλήματα, υστερούν όμως σε ακρίβεια. Μια σχετικά νέα τεχνική με ευρεία εφαρμογή στην ιατρική απεικόνιση είναι τα ενεργά περιγράμματα (active contours). Πρόκειται για παραμετρικές καμπύλες που κινούνται στο επίπεδο της εικόνας έτσι ώστε να ελαχιστοποιείται ένα ενεργειακό συναρτησιακό και επιτρέπουν την ανίχνευση αντικειμένων στην εικόνα. Στις κλασικές μεθόδους των ενεργών περιγραμμάτων, η αρχική καμπύλη πρέπει να ορίζεται κοντά στο προς ανίχνευση αντικείμενο. Για την αντιμετώπιση του προβλήματος αυτού έχουν προταθεί διάφορες βελτιώσεις του κλασικού μοντέλου των ενεργών περιγραμμάτων, όπως η εισαγωγή της λεγόμενης «δύναμης μπαλονιού». Τα ενεργά περιγράμματα μπορούν να χρησιμοποιηθούν και για παρακολούθηση κίνησης σε ακολουθίες εικόνων, καθώς μπορούν να προσαρμόζονται στα εξέχοντα χαρακτηριστικά των κινούμενων δομών. Ωστόσο, στην υπερηχητική απεικόνιση των αρτηριακών τοιχωμάτων, η περιπλοκότητα της κίνησής τους και ο έντονος θόρυβος καθιστούν ιδιαίτερα δύσκολη την άμεση εφαρμογή των ενεργών περιγραμμάτων για την παρακολούθηση κίνησης. Στόχος της παρούσας εργασίας είναι ο συνδυασμός των ενεργών περιγραμμάτων και των μεθόδων ταύτισης περιοχών για την αυτοματοποίηση της παρακολούθησης κίνησης σε ακολουθίες εικόνων των τοιχωμάτων αρτηριών (συγκεκριμένα της καρωτιδικής και της βραχιακής) και για τη βελτίωση της επαναληψιμότητας των σχετικών μετρήσεων. Αρχικά, εφαρμόστηκαν οι μέθοδοι ταύτισης περιοχών ενός επιπέδου (Single Level Block Matching) και πολλών επιπέδων (Multilevel Block Matching) για την παρακολούθηση της κίνησης των αρτηριακών τοιχωμάτων από ακολουθίες εγκάρσιων τομών της καρωτιδικής και της βραχιακής αρτηρίας. Μια κλειστή καμπύλη ορίστηκε από το χρήστη στο πρώτο πλαίσιο της ακολουθίας, έτσι ώστε να αντιστοιχεί κατά προσέγγιση στο περίγραμμα των ορίων του αρτηριακού τοιχώματος και καταγράφηκε η επιφάνεια που περικλείεται από την καμπύλη αυτή κατά τη διάρκεια ενός καρδιακού κύκλου. Η μετατόπιση των σημείων της καμπύλης από πλαίσιο σε πλαίσιο εκτιμήθηκε με τις μεθόδους ταύτισης περιοχών. Η μορφή της γραφικής παράστασης της επιφάνειας αυτής σε συνάρτηση με το χρόνο (δηλαδή τον αριθμό του πλαισίου) αποτελεί έναν πολύ καλό δείκτη της κατάστασης της αρτηρίας. Η αυτοματοποίηση της διαδικασίας λήψης των παραπάνω μετρήσεων μπορεί να επιτευχθεί αν η επιλογή της αρχικής κλειστής καμπύλης δεν βασίζεται στην εκτίμηση του χρήστη αλλά στην ανίχνευση των τοιχωμάτων με ενεργά περιγράμματα. Το κλασικό μοντέλο των ενεργών περιγραμμάτων και το μοντέλο της «δύναμης μπαλονιού» εφαρμόστηκαν για αυτό το σκοπό στο πρώτο πλαίσιο των ακολουθιών εικόνων των αρτηριών. Διαπιστώθηκε ότι το μοντέλο της δύναμης μπαλονιού δίνει ικανοποιητικά αποτελέσματα ανίχνευσης των αρτηριακών τοιχωμάτων και μάλιστα με ικανοποιητική επαναληψιμότητα, καθώς το αποτέλεσμα της ανίχνευσης δεν διαφοροποιούνταν σημαντικά από την επιλογή της αρχικής κλειστής καμπύλης του ενεργού περιγράμματος, αρκεί η ακτίνα της τελευταίας να είναι τέτοια ώστε η καμπύλη να βρίσκεται εξ ολοκλήρου στο εσωτερικό της αρτηρίας. Στη συνέχεια, η καμπύλη που προέκυψε από την ανίχνευση των τοιχωμάτων χρησιμοποιήθηκε ως αρχική καμπύλη για την παρακολούθηση κίνησης με τις μεθόδους ταύτισης περιοχών. Τα αποτελέσματα που προέκυψαν δεν διαφέρουν σημαντικά σε σχέση με την περίπτωση όπου ο ορισμός της καμπύλης στο πρώτο πλαίσιο γίνεται από το χρήστη. Συνεπώς, η ανίχνευση των αρτηριακών τοιχωμάτων με ενεργά περιγράμματα μπορεί να χρησιμοποιηθεί για να βελτιώσει την επαναληψιμότητα των μετρήσεων για την παρακολούθηση κίνησης και να συμβάλει στην αυτοματοποίηση της διαδικασίας λήψης τους. / Cardiovascular diseases are the leading cause of death today in developed countries. Their causes are very frequently related with the status of artery walls. Ultrasonic imaging is very important for the diagnosis of possible arterial pathology, because it is of low cost, safe for the patient and can be performed in real time. Ultrasonic imaging also allows arterial wall motion tracking, which can provide critical diagnostic information. Motion tracking methods include Tissue Doppler Imaging (TDI), differential optical flow methods and block matching. Tissue Doppler Imaging offers excellent accuracy, restricted however to directions close to the direction of the ultrasonic beam. Optical flow methods can be used in two dimensions with considerable accuracy, but they fail in cases of fast moving structures. In the case of block matching, no such problems have to be dealt with, however with significant cost in accuracy. Active contours, a relatively new technique widely used in medical imaging, are parameterized curves moving on the image plane in order to minimize an energy functional and allowing object detection. Classical active contour methods require that the initial curve of the model is defined close to the object to be detected. In order to avoid this, several techniques have been proposed, such as the so-called “balloon force”. Active contours can also be used for motion tracking in series of image frames, provided that they can fit to salient features of moving structures. In arterial wall ultrasonic imaging however, motion complexity and noise obstruct motion tracking with active contours. In the current study active contours and block matching methods are combined to improve reproducibility of motion tracking measurements in series of artery wall images (namely for the carotid and brachial artery). Single level and multilevel block matching methods were used for artery wall motion tracking. A closed curve was defined by the user in the first frame of the image series, both for the carotid and brachial artery. This curve is a rough estimation of the arterial wall contour. The area enclosed by the curve is recorded throughout a cardiac cycle. Curve movement is estimated with block matching methods. The graph pattern of enclosed area versus time (i.e. frame number) is a very good indicator for the status of the artery. The above process can be automatized if the initial closed curve is produced by object detection with active contours and not by estimation. The active contours classical model and the balloon force model were used for artery wall detection in the first frame of the artery image series. The balloon force model yielded satisfactory wall detection results with considerable reproducibility. The choice of the dimensions of the initial contour of the model did not affect the final result considerably, provided that the initial contour is fully placed inside the arterial lumen. The curve that resulted from object detection was used to initialize the motion tracking process with block matching methods. In this way, similar motion tracking results can be obtained for the artery image series, but with much improved reproducibility.

Cette étude s’inscrit dans le cadre de l’inspection en service des soudures des réacteurs nucléaires de génération IV, en vue de contribuer à la démonstration de sûreté. La structure anisotrope et hétérogène des soudures multipasses en acier inoxydable austénitique rend leur contrôle ultrasonore difficile. Ainsi, afin d'interpréter correctement les signaux mesurés et de caractériser les défauts potentiels, une description de la soudure est utilisée. Elle constitue la connaissance a priori introduite dans la méthode de l'Energie Topologique. L’étude réalisée se décline en deux temps : le développement de la méthode en milieu borné et sa comparaison avec le Matched Field Processing, puis son application au cas de soudures réelles. L'extension de la méthode de l'Energie Topologique aux milieux bornés isotropes et homogènes vise à tirer parti des réflexions multiples. Plusieurs solutions du problème numérique de propagation, obtenues pour différentes conditions aux frontières, sont judicieusement associées afin de sélectionner les échos de diffraction porteurs d'information. Selon le type de défaut à imager des énergies topologiques spécifiques sont définies. La technique est introduite analytiquement avant d'être validée numériquement puis expérimentalement.Dans un second temps, la méthode est appliquée au milieu complexe de la soudure. La procédure est testée expérimentalement sur des soudures réelles afin d'évaluer les performances en localisation. Cependant, en raison de la variabilité de la structure, la qualité de l'image peut se dégrader selon les cas d'étude. La possibilité de générer des sources arbitraires permet de pallier en grande partie cette difficulté. / The present study has been done as part of the in-service inspection of weld structure belonging to generation IV nuclear reactors. It aims at checking both the safety and integrity of these components. The anisotropic and heterogeneous structure of austenitic stainless steel welds disturbs the ultrasonic non destructive testing. Thus, a weld description model is necessary to properly analyze the ultrasonic measured signals and to characterize potential flaws. The weld model makes a priori knowledge up in the Topological Energy method. The study is divided into two parts: development of the method in a bounded medium and comparison with the Matched Field Processing method, and then its application to real weld structures.The work firstly focuses on expanding the Topological Energy method to isotropic and homogeneous bounded medium to take advantage of multiple reflections between the flaw and edges. For that, different conditions are numerically applied to boundaries. By adding up these conditions it becomes possible to select the appropriate scattering signal. Modified topological energies are defined according to the type of analyzed flaws. The approach is analytically demonstrated before being validated firstly from synthetical data and then from experimental data.The second part deals with the application of the method to the complex weld structure. The process is experimentally tested on welds in order to evaluate efficiency of flaws localization. However, the image's quality can be deteriorated because of variability of the structure. By generating arbitrary ultrasonic source this difficulty is mostly overcame.