Nos últimos anos, o treinamento aeróbio vem sendo empregado como forma de recuperação da marcha em pessoas pós-acidente vascular cerebral. O objetivo desta Tese foi avaliar os efeitos do treinamento aeróbio em piscina e em esteira rolante na marcha de indivíduos hemiparéticos crônicos. Participaram 12 pessoas, randomizadas por sorteio para Grupo Piscina e Grupo Esteira. Para as avaliações funcionais, os testes e escalas foram divididos de acordo com a Classificação Internacional de Funcionalidade, Incapacidade e Saúde: Avaliação Fugl-Meyer; a Escala de equilíbrio de Berg, Escala de avaliação do controle postural para pacientes pós-acidente vascular cerebral, Timed Up and Go Test e o Questionário de qualidade de vida SF-36. Na avaliação biomecânica foram avaliados os parâmetros cinemáticos de amplitude de movimento, ângulo mínimo e máximo da articulação do joelho e tornozelo e parâmetros eletromiográficos (EMG) dos músculos tibial anterior, gastrocnêmio lateral, reto da coxa, vasto lateral, bíceps da coxa, semitendíneo. Foi realizada análise de variância para inferir o efeito do treinamento aeróbio em ambos os grupos. Para estudar o comportamento das variáveis eletromiográficas em função das avaliações funcionais foi realizada a análise de regressão linear múltipla. O treinamento aeróbio melhorou o comprometimento sensório-motor, equilíbrio, agilidade e qualidade de vida relacionada à saúde dos participantes de ambos os grupos, como alterações nos padrões eletromiográficos dos músculos na locomoção dos participantes de ambos os grupos. Não houve efeito do treinamento aeróbio para os parâmetros cinemáticos das articulações analisadas. Houve a fraca relação entre os parâmetros EMG e as variáveis funcionais. Os participantes foram beneficiados pela prática do treinamento aeróbio que propiciou a melhora da funcionalidade dos participantes, independente do meio o qual foi realizado / Stroke is the leading cause of adult disability in the world. Clearly, walking retraining is a major goal in a rehabilitation program for person with stroke. Our study was designed to evaluate the effect of a training program involving both treadmill and aquatic walking to reduce the disability due to poor walking performance in chronic stroke persons. Twelve participants were randomly assigned to treadmill group and aquatic group for the 9 week program (3 days/week) progressive graded, high-intensity aerobic treadmill exercise or aquatic exercise. Data from functional assessments were selected according to levels of the International Classification of Functioning, Disability and Health: Fulg-Meyer scale to body function, Brazilian Berg balance scale, Timed and up & go test and The Postural Assessment Scale for Stroke Patients to activity and Medical Outcomes Study short-form 36-item questionnaire (SF-36) to participation. Biomechanical data were the lower limb kinematic variables (peak and minimal angle and maximal range) and surface electromyogram signals was recorded from tibialis anterior, lateral gastrocnemius, rectus femoris, vastus lateralis, biceps femoris and semitendinosus bilaterally during gait. A five-way analysis of variance was performed to test for differences among groups, phases, muscles, sides and gait phases. Multiple linear regression models were ran to examine the relationships between functional assessment and the electromyography variables. The aerobic training improved the functional variables in both groups. The electromyography variables showed influence of the training program in both groups. Weak relationship exists between functional assessment and the electromyography variables. The aerobic training programs in chronic hemiparetic stroke were beneficial and improving functional status in stroke person for both groups

Com a transição epidemiológica no Brasil, as doenças crônicas passaram a ser responsáveis pelo maior número de óbitos entre homens e mulheres. Entre os componentes que definem o estado de saúde humana, alguns do contexto geográfico, como clima local e fatores socioeconômicos, parecem influenciar na mortalidade por doenças do aparelho circulatório, tais como no acidente cerebral vascular (AVC) e na embolia pulmonar (EP). O objetivo principal deste trabalho foi verificar a influência do contexto geográfico (variáveis meteorológicas, índice climático e fatores socioeconômicos) na mortalidade por doenças do aparelho circulatório (AVC e EP) no município de São Paulo, no período de 2002 a 2011. Para analisar a associação da mortalidade com as variáveis meteorológicas foi utilizado um modelo linear generalizado empregando-se o método de Poisson e os modelos de lags distribuídos. Espacialmente a associação da mortalidade com as variáveis socioeconômicas foram testadas utilizando-se os modelos de regressão espacial OLS e GWR. Como resultado encontramos que tanto o frio quanto o calor são fatores de risco para todos os tipos de AVC e EP, com risco maior dependendo do tipo em homens e mulheres. Espacialmente os valores mais elevados do risco relativo (RR) da mortalidade por AVC estavam concentrados nas regiões periféricas do municipio de São Paulo, o que coincidiu com as áreas de menor renda per capita e vegetação e maior porcentagem de população preta. Já com relação à distribuição espacial dos altos valores de RR por EP esses estavam presentes principalmente na região central do município. Concluindo, a nossa pesquisa gerou grande quantidade de resultados que mostram que tanto as variáveis ambientais como socioeconômicas têm influência na mortalidade por algumas doenças do aparelho circulatório. Tendo em vista que o atendimento de urgência para os casos de AVC e EP pode evitar óbitos e sequelas graves, a melhor compreensão da importância do contexto geográfico pode permitir o desenvolvimento de sistemas de alertas junto aos serviços de atendimento de urgência e o direcionamento de campanhas para a prevenção dos fatores de risco evitáveis. / With the epidemiological transition in Brazil, chronic diseases are now responsible for more deaths among men and women. Among the components that define the state of human health, some geographical context, as local climate and socioeconomic factors appear to influence the mortality from circulatory diseases, such as in stroke and pulmonary embolism (PE). The main objective of this study was to investigate the influence of the geographical context (meteorological variables, climate index and socioeconomic factors) in mortality from cardiovascular diseases (stroke and PE) in São Paulo, between 2002 to 2011. In order to analyze the association of mortality with the meteorological variables we used a generalized linear model using the Poisson distribution and distributed lag non linear models. Spatially the association of mortality with socioeconomic variables were tested using the spatial regression models OLS and GWR. As a result we found that both the cold and the heat are risk factors for all types of stroke and PE with a higher risk depending on the type of men and women. Spatially the highest values of relative risk (RR) for stroke mortality were concentrated in the outskirts of the city of São Paulo, which coincided with areas of lower per capita income and vegetation and higher percentage of black population. In relation to spatial distribution of high values of RR PE by these were present mainly in the inner area. In conclusion, our research has generated a lot of results that show that both environmental and socioeconomic variables influence on mortality from some diseases of the circulatory system. In view of the urgent care for stroke and PE cases can avoid serious sequelae and deaths, a better understanding of the importance of geographic context may allow the development of warning systems at the urgent care services and targeting campaigns for the prevention of avoidable risk factors.

Au décours d’un AVC, près de 50% des patients vont développer un trouble de la cognition dans les six premiers mois suivant l’accident. Ces déficits ont la particularité de pouvoir être de natures différentes, en touchant plusieurs domaines cognitifs distincts, parfois simultanément. A l’aide de batteries de tests neuropsychologiques dédiés, ces altérations cognitives ont pu être largement décrites et caractérisées. En revanche, les mécanismes sous-jacents l’apparition de ces troubles sont encore mal compris.Grâce aux possibilités d’analyse structurelle et fonctionnelle du cerveau, l’imagerie par résonance magnétique (IRM) est une technique de plus en plus utilisée pour identifier de nouveaux marqueurs diagnostiques des maladies neurodégénératives. L’objectif principal de de travail de thèse était de mieux comprendre les mécanismes physiopathologiques impliqués dans l’apparition de troubles cognitifs post-AVC à l’aide de méthodologies avancées en IRM.La première étude est une étude transversale comportant un versant pré-clinique chez des rats ischémiés et un versant clinique chez des patients victimes d’un AVC. Chez l’Homme, les résultats ont montré des anomalies morphologiques de l’hippocampe ainsi que des anomalies structurelles du cortex entorhinal chez les patients présentant un déficit cognitif 6 mois après AVC. Chez le rongeur, l’imagerie a montré des déformations des contours de l’hippocampe chez les rats ischémiés présentant des anomalies cognitives 6 mois après occlusion de l’artère cérébrale moyenne.Nous avons ensuite analysé les anomalies de connectivité fonctionnelle spécifiques aux troubles cognitifs survenant dans les 6 mois après un AVC chez l’Homme car certains travaux ont démontré l’importance des anomalies de communication fonctionnelle dans l’apparition des troubles cognitifs post-AVC. Nous avons ainsi identifié un réseau fonctionnel spécifique organisé autour du lobe frontal supérieur et temporal. De plus, chaque fonction cognitive était associée à un motif spécifique de connexions fonctionnelles altérées.Enfin, à l’aide d’algorithmes d’apprentissage machine, nous avons montré que ce réseau fonctionnel impliqué dans la génèse des troubles cognitifs post-AVC était un excellent marqueur prédictif des altérations cognitives chez l’Homme 3 ans après l’AVC.Ainsi, les mesures morphométriques du lobe temporal médian et de connectivité fonctionnelle globale apparaissent comme des marqueurs IRM complémentaires dans la caractérisation des troubles cognitifs post-AVC. L’ensemble de ces résultats suggèrent ainsi que des mécanismes physiopathologiques spécifiques seraient impliqués dans la survenue de des troubles cognitifs, permettant d’envisager dans l’avenir des prises en charge personnalisées pour les fonctions cognitives des patients victimes d’AVC. / After a stroke, nearly 50% of the patients are prompt to develop cognitive disorders in the first 6 months. These deficits can be various, affecting distinct cognitive functions and sometimes simultaneously. Using specific cognitive battery, these disorders can be well described and characterized. However, the mechanisms leading to the development of these cognitive impairments are poorly understood.In that sense, magnetic resonance imaging offers many possibilities for the detection of occurring cognitive disorders after a stroke. The aim of this study of to better define imaging markers that could help to better understand the physiopathology and potentially, using advances methods, predict the long-term outcome of stroke patients.First, a translational study highlighted morphological deformations of hippocampus and structural changes of entorhinal cortex in patients with a cognitive disorder 6 month after stroke compared to patients without. These alterations have also been found in a rat model of ischemia, that presented deformations of hippocampus 6 months after the ischemia compared to control animals.Second, many imaging studies reported that the post-stroke cognitive disorders could be more associated with spread dysfunctions rather than focal alteration at the lesion site. In that sense, we analyzed the functional alterations that could exist in patients with a cognitive disorder 6 months post-stroke compared to patients without. We then identified a functional network that seemed to be organized around regions in superior frontal and temporal lobes. Moreover, each cognitive function presented specific pattern of correlated connections in this network.Lastly, using machine learning algorithms, we showed that this identified functional network 6 months post-stroke can predict the diagnosis of cognitive impairment 30 months later, and also predict alterations of specific cognitive domains at the same time.Then, morphological measures of the medial temporal lobe and the global functional connectivity analyses appeared to be complementary MRI markers for the characterization of patients developing a cognitive disorder after stroke. All these results suggest then that specific physiopathological mechanisms could be involved in the appearance of post-stroke cognitive disorders, permitting to imagine potential new personalized care of post-stroke cognitive disorders.

Introdução: As doenças cerebrovasculares são consideradas atualmente a segunda principal causa de óbito no mundo e a terceira causa de anos de vida perdidos por mortalidade1,2. A aterosclerose de grandes artérias é uma das principais condições subjacentes associadas ao AVC isquêmico (AVCi) e correlaciona-se com maiores taxas de recorrência. A detecção e a estratificação da estenose extracraniana podem ser feitas através do Doppler, da angiotomografia computadorizada (ATC), da angiorressonância magnética (ARM) e da angiografia intra-arterial digital (AIA), sendo esta última considerada o método padrão-ouro. Objetivo: Avaliar a acurácia diagnóstica e a concordância entre os métodos de ATC, ARM com contraste (AM CC) e AIA na análise da estenose extracraniana. Determinar a frequência e caracterizar a estenose extracraniana em população brasileira sintomática. Metodologia: Foram avaliados retrospectivamente os exames AIA, ATC e ARM, de pacientes adultos sintomáticos admitidos na Unidade de Emergência do Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto (UE HCFMRP) no período 03/2014-03/2015, para detecção e estratificação da estenose extracraniana. Foram coletados ainda dados demográficos, clínicos e laboratoriais desses pacientes. Resultados: Observou-se alta acurácia da ATC e da ARM na avaliação de segmentos carotídeos, com sensibilidade de 100% e especificidade variando entre 78% e 100% para estenoses >=50%. Para segmentos vertebrais, observou-se menor acurácia dos métodos, sobretudo da ARM, com valores de sensibilidade e especificidade variando entre 60%-85% e 33-62%, respectivamente, para estenoses >=50%. A prevalência de estenose extracraniana >=50% em nossa população foi de 38,6% e de 23,4% para estenoses >=70%. O segmento vascular mais acometido foi a origem das artérias vertebrais. Os fatores de risco associados a estenose extracraniana foram: sexo masculino, idade avançada, tabagismo e elevada pressão arterial sistólica na admissão. Conclusão: A ATC e ARM representam métodos adequados para investigação de estenoses extracranianas, sobretudo carotídeas. Ambos os métodos, sobretudo a ARM, têm acurácia limitada na avaliação dos óstios vertebrais. / Introduction: Cerebrovascular diseases are considered the second cause of death worldwide and the third cause of years of life lost (YLL)1,2. Large arteries atherosclerosis is one of the main conditions associated with stroke and correlates with higher recurrence rates. Imaging methods such as Doppler, computed tomography angiography (CTA), magnetic resonance angiography (MRA) and intra-arterial angiography (IAA) are available for extra cranial vascular study. Intra-arterial angiography remains the gold standard. Objectives: Evaluate diagnostic accuracy and concordance between CTA, MRA (contrast enhanced) and IAA for extracranial stenosis analysis. Determine frequency and distribution of extra cranial stenosis in a brazilian symptomatic population. Methods: IAA, CTA and MRA exams from adult symptomatic patients admitted between 03/2014 and 03/3015 at the Emergency Unit of Clinics Hospital of Ribeirão Preto\'s School of Medicine were retrospectively reviewed for detection and grading of extra cranial stenosis. Clinical and laboratorial information from patients was obtained. Results: Both CTA and MRA showed high sensitivity (100%) and specificity (78%-100%) in the evaluation of carotid vessels for stenosis >=50%. However, lower sensitivity (60-85%) and specificity (33-62%) were obtained for vertebral segments, Extra cranial stenosis prevalence was 38,6% for stenosis >=50% and 23,4% for stenosis >=70% among our patients. Vertebral artery origins were the most affected segments. Risk factors identified for extra cranial stenosis were: male gender, age, smoking and high systolic blood pressure on admission. Conclusions: CTA and MRA are considered adequate methods for extra cranial stenosis, specially for carotid segments. Both methods have lower accuracy in the investigation of vertebral artery origins.

L’objectif de ce travail était d’’évaluer les effets d’un programme d’incitation et d’éducation à l’activité physique, à domicile chez des patients post-AVC en phase subaiguë, sur la performance au test de marche de 6 minutes (TM6M) et son maintien à six mois de l’arrêt du programme. Il s’agissait d’un essai clinique comparative, prospective, randomisée, en simple aveugle et monocentrique. La population de l’étude était composée de 84 patients post-AVC (Age 61.7 ± 13.2 ans, délai de l’AVC 2.5 ± 1.5 mois). Quarante-deux patients ont été randomisé pour le GE et 42 patients pour le GC. Le GE a suivi un programme d’incitation à l’AP à domicile pendant 6 mois. Trois moyens d’incitation ont été utilisés ; un accéléromètre (Armband Sensewear, Bodymedia), des appels téléphoniques hebdomadaires et des visites à domicile toutes les trois semaines. Également, une séance d’éducation sur l’AP et la fixation des objectives en termes du nombre de pas et de la durée de l’AP a été réalisée avant de commencer le protocole. Le GC a reçu simplement une information sur les bienfaits de l’AP et sur le niveau d’activité à réaliser selon les recommandations de pratique post-AVC. Les critères d’évaluation secondaires ont été l’échelle « fonctionnal ambulation classification » (FAC), l’indice de barthel (IB), l’indice moteur (IM), la qualité de vie (Euroqol-5D), la composition corporelle, le questionnaire « Health Care Comunication Questionnaire » (HCCQ), l’Echelle Visuelle Analogique de la douleur (EVA), le questionnaire Hospital Anxiety and Depression Scale (HADS) et questionnaire Multidimensionnal fatigue Inventory 20 (MFI-20). Les patients ont été évalué avant (T0), après l’intervention (T1) et six mois après l’arrêt du programme (T2). Les résultats montrent une augmentation significative de la distance de marche parcoure entre T0 et T1 pour le GE (18%, p<0.001), malgré cette augmentation, il n’y a pas de différence entre GE et GC à T1 (p=0.30). Une augmentation significative du score de FAC (+0.75, p=0.02) a été constaté pour le GE à T1, cette augmentation était différente entre les deux groupes (p=0.0013). A l’inverse, une diminution significative du score MFI-20 (-4.6, p<0.001) a été constaté pour le GE à T1, cette diminution était différente entre les deux groupes (p<0.001). A T2 les effets du programme sur le périmètre de marche (p=0.75), la capacité fonctionnelle (p=0.17) et la fatigue (p=0,74) se sont maintenus. Aucun effet n’a été constaté pour le reste des variables. De plus, en fin d’intervention le GE atteint les recommandations d’AP par jour, en termes de pas (5955 ± 5475) et de durée (105 ± 75 minutes). / The aim of the study was to evaluate the effect of a home-based physical activity incentive program on the 6 minutes walking distance performance (6MWT) and its evolution, 6 months after the end of the program. This is a comparative, prospective, randomized, single-blind and monocentric clinical trial. Participants were 84 post-stroke patients (average age 61.7 ± 13.2 years, time since stroke 2.5 ± 1.5 months). Forty-two patients were randomly assigned to an experimental group (EG) and the other forty-two to a control group (CG). EG followed a home-based physical activity incentive program for 6 months. Three incentive methods have been used; an accelerometer (Armband Sensewear, Bodymedia), weekly telephone calls, and home visits every three weeks. In addition, educational session about physical activity and information about physical activity recommendations were conducted before the start of the protocol. CG received general information about physical activity benefits and post-stroke practicing activity recommendations. Other assessment criteria were functional ambulatory classification (FAC), barthel index (BI), motricity index (MI), quality of life (Euroqol-5D), body composition, the health care communication questionnaire (HCCQ), visual analog scale of pain (VAS), the hospital anxiety and depression scale (HADS), the multidimensional fatigue inventory 20 questionnaire (MFI-20). Patients were evaluated before intervention (T0), after intervention (T1) and 6 months after the end of the program (T2). Walking distance increased significantly in the EG between T0 and T1 (18%, p<0.001); however, there was not a significantly difference between EG and CG at T1 (p=0.30). The score of FAC increased significantly (+0.75, p=0.02) in EG at T1, but it was different between EG and CG (p=0.0013). Furthermore, MFI-20 score decreased significantly at T1 (-4.6, p<0.001) for the EG, it results was different between both groups (p<0.001). The program effects on walking distance (p=0.75), functional ability (p=0.17), and fatigue (p=0.74) at T2 were maintained. No significant effect of other variables was found. In addition, at the end of the program, the EG achieved the physical activity recommendation per day, step number (5955 ± 5475) and activity duration (105 ± 75 minutes).

Doenças como AVC e Epilepsia estão constantemente associadas à manifestação de comprometimentos cognitivos e demência, tendo como característica principal os déficits de memória. Atualmente,o instrumento Mini Exame do Estado Mental (MEEM) é o teste de rastreio de comprometimento cognitivo mais utilizado no mundo, individualmente ou como parte integrante em baterias de avaliação neuropsicológica. Devido afalta de instrumentos específicos pararastreiode comprometimento cognitivo de indivíduos com sintomas de demênciavítimas de AVC e/ou Epilepsia em Angola, África, fez se necessária aadaptação evalidação de instrumentos confiáveis.O presente estudoteve por objetivo a avaliação clínicada versão brasileira do instrumento MEEM adaptado por Brucki, para uso na população adulta de Angola.Trata-se de um estudo clínico comparado, envolvendo três populações. Foram incluídos neste estudo 85 indivíduos acometidos por AVC, 40 por Epilepsia e como grupo de comparação, 87 indivíduos de 20 a 65 anos de idade, supostamente saudáveis. A escolaridade mínima para inclusão do estudo foi definida em 4 anos de ensino formal. O presente estudo foi desenvolvido em parceria com o Serviço de Neurologia do Hospital Américo Boavida e com a Faculdade de Medicina da Universidade Agostinho Neto (FMUAN), ambos localizados ao norte da cidade de Luanda, capital de Angola, África.Toda a amostra foi submetida à coleta de dados sócio demográficos e avaliação neuropsicológica, através do instrumento MEEM. O instrumento consistiu no rastreio de comprometimento cognitivo, contemplando funções como orientação temporal e espacial, memória, cálculo, linguagem e capacidade construtivavisual.No presente estudo, encontramos dados que apontam um desempenho significativamente pior das funções cognitivas em pacientes acometidos por AVC quando comparados a pacientes com Epilepsia e grupo dossaudáveis. Esses achados confirmam a validade do instrumento MEEM, em função das características apresentadas pela doença, sendo possível discriminar com clareza os grupos AVC, Epilepsia e Controles Saudáveis. Os dados obtidos indicam uma boa qualidade da versão na língua portuguesa angolana, sendo a consistência interna da versão adaptada com ? de Cronbach = 0,736, semelhante aos dados de referência. Este estudo pioneiro preenche uma importante lacuna na produção de conhecimento em Angola, abrindo um leque de possibilidades para outros trabalhos científicos no país, facilitando a aplicação dos resultados tanto na área acadêmica-científica, quanto na clínica. É necessário aos profissionais de saúde que se apropriem de mais conhecimentos, para que possam propor intervenções adequadas, que auxiliam nos direitos de saúde e bem-estarda população angolana. / Diseases such as stroke and epilepsy are constantly associated with the manifestation of cognitive impairment and dementia, having as main feature the memory deficits (Caramelli & Castro, 2005). Currently, the instrument Mini Mental State Examination (MMSE) is the screening test of cognitive impairment most used in the world, individually or as an integrated part in neuropsychological assessment battery (Melo & Barbosa, 2015). Due to the lack of specific instruments for screening cognitive impairment of individuals with dementia symptoms victims of stroke and / or epilepsy in Angola, Africa, it was necessary to adapt and validate reliable instruments. The presentestudy had as objective the clinical evaluationof the brazilian version of the MMSE instrument adapted by Brucki et al. (2003), for use in the adult population of Angola, Africa. It is a comparative clinical study involving three populations. This studyincluded 85 individuals affected by stroke, 40 by Epilepsy, and as a comparison group, 87 individuals, 20 to 65 years of age, who were supposed to be healthy. The minimum schooling for inclusion of the study was defined in 4 years of formal education. Thepresent study was developed in partnership with the Neurology Service of the Américo Boavida Hospital and the Faculty of Medicine of the Agostinho Neto University (FMUAN), both located north of the city of Luanda, the capital of Angola, Africa. All the sample was submitted to the collection of sociodemographic data and neuropsychological evaluation, through the MMSE instrument. The instrument consisted in the screening of cognitive impairment, including functions such as temporal and spatial orientation, memory, calculus, language and visual constructive capacity.In the presente study, we found data that indicate a significantly worse performance of cognitive functions in patients with stroke when compared to patients with epilepsy and healthy group. These findings confirm the validity of theinstrument MMSE in, due to the characteristics of the disease, being possible to discriminate with clarity the groups Stroke, Epilepsy and Healthy Controls. The data obtained indicate a good quality of the Angolan Portuguese language version, being the internal consistency of the adapted versionwhit the Cronbach\'s alpha = 0.736, similar to the reference data.This pioneering study fills animportant gap in knowledge production in Angola, opening up a range of possibilities for other scientific papers in the country, facilitating the application of the results both in the academic and scientific area, as at the clinic. It is necessary that health professional take ownership of more knowledge, so that they can propose appropriate interventions that assist in health and welfare rights of the Angolan population.

Cette thèse s'intéresse à améliorer les codeurs vidéo actuels tels que H.264 MPEG-4/AVC en utilisant avantageusement des informations structurelles contenues dans les images codées. Dans ce contexte, on observe que tous codeurs vidéo utilisent une étape de transformation permettant de décorréler mathématiquement les informations traitées afin d'en diminuer le coût de codage entropique. D'autre part, on remarque que toutes les images traitées qu'elles soient prédites ou non, possèdent des structures géométriques très marquées. Une étude des transformées existantes et possibles pour ces codeurs vidéo montre que peu d'entre elles (DCT, en ondelettes, à recouvrement, DCT sous forme lifting...) permettent de représenter efficacement ces structures géométriques des images. L'état de l'art de ces transformées exploitant les structures géométriques est porté historiquement par les ondelettes de seconde génération comme les contourlets, les bandelettes ou les directionlets. Mais, plusieurs études plus récentes utilisent des approches DCT, basées blocs, avec des orientations afin de mieux représenter ces structures géométriques. L'objectif de notre étude est d'améliorer le codage des images résiduelles H.264/AVC, issues de prédictions spatiales (Intra) ou temporelles (Inter), en utilisant leurs structures géométriques. Une première approche de ce travail de thèse nous a conduits à analyser et exploiter des méthodes connues de l'état de l'art. Pour cela, nous avons déni un schéma sous forme lifting réalisant les opérations de la DCT H.264/AVC. Ce schéma permet de voir cette DCT comme une transformée en ondelettes et donc de disposer d'une approche commune. On peut alors lui appliquer des outils de seconde génération an qu'elle représente au mieux les structures géométriques des images. Et, une version de transformée à recouvrement en pré- et post-traitements a été utilisée dans le codeur H.264/AVC. Une seconde approche de nos recherches a été de dénir une méthode d'orientation par pré- et post-traitements associée à un parcours adapté des coefficients quantifiés produits. Le pré-traitement de cette méthode d'orientation réalise des pseudo-rotations permettant de redresser les blocs des images vers l'horizontale ou la verticale. Cette opération est réalisée par cisaillements, soit par permutations circulaires des pixels, améliorant la décorrélation de la DCT qui suit sans présenter les défauts inhérents aux approches de l'état de l'art. Cette méthode, insérée dans un codeur H.264/AVC, présente de bonnes performances de codage. Cependant, le coût des informations d'orientation, sélectionnées selon un critère débit-distorsion, est élevé dégradant ces performances dans les bas débits, la méthode restant plus efficace que H.264/AVC dans les hauts débits (QP < 30). Les coefficients quantifiés issus de la méthode d'orientation précédente sont ensuite parcourus à la verticale, à l'horizontale ou en zigzag suivant les redressements appliqués ou le type de partitions. Cette adaptation de parcours permet de légèrement conserver du débit améliorant ainsi notre méthode globale qui devient plus efficaces que H.264/AVC dans les moyens débits (QP < 35).

<p>To provide universal multimedia experience, multimedia streaming services need to transparently handle the variation and heterogeneity in operating environment. From the standpoint of streaming application, video adaptation techniques are intended to cope with the environmental variations by utilizing manipulations of the video content itself. Scalable video coding (SVC) schemes, like that suggested by the standards H.264 and its SVC extension, is highly attractive for designing a self-adaptive video streaming system. When SVC is employed in streaming system, the produced video stream can be then easily truncated or tailored to form several sub-streams which can be decoded separately to obtain a range of preferable picture size, quality and frame rate. However, questions about how to perform the adaptation using SVC and how much adaptation SVC enables are still remaining research issues. We still lack a thorough understanding of how to automate the scaling procedure in order to achieve an optimal video Quality-of-Experience for end users.</p><p>Video QoE, depends highly on human perception. In this thesis, we introduce several video QoE studies around the usability of H.264 SVC. Several factors that contribute significantly to the overall QoEs have been identified and evaluated in these studies. As an example of application usage related factor, playback smoothness and application response time are critical performance measures which can benefit from temporal scalability. Targeting on applications that requires frequent interactivity, we propose a transcoding scheme that fully utilizes the benefits of Switching P and Switching I frames specified in H.264 to enhance video stream's temporal scalability.  Focusing on visual quality related factors, a series of carefully designed subjective quality assessment tests have been performed on mobile devices to investigate the effects of multi-dimensional scalability on human quality perception. Our study reveals that QoE degrades non-monotonically with bitrate and that scaling order preferences are content-dependent. Another study find out that the flickering effect caused by frequent switching between layers in SVC compliant bit-streams is highly related to the switching period. When the period is above a certain threshold, the flickering effect will disappear and layer switching should not be considered as harmful. We have also examined user perceived video quality in 3D virtual worlds. Our results show that the avatars' distance to the virtual screen in 3D worlds contribute significant to the video QoE, i.e., for a wide extent of distortion, there exists always a feasible virtual distance from where the distortion is not detectable for most of people, which makes sense to perform video adaptation.</p><p>The work presented in this thesis is supposed to help improving the design of self adaptive video streaming services that can deliver video content independently of network technology and end-device capability while seeking the best possible experience for video.</p> / Ardendo småföretagsdoktorand

Video codec compresses the input video source to reduce storage and transmission bandwidth requirements while maintaining the quality. It is an essential technology for applications, to name a few such as digital television, DVD-Video, mobile TV, videoconferencing and internet video streaming. There are different video codecs used in the industry today and understanding their operation to target certain video applications is the key to optimization. The latest advanced video codec standards have become of great importance in multimedia industries which provide cost-effective encoding and decoding of video and contribute for high compression and efficiency. Currently, H.264 AVC, AVS, and DIRAC are used in the industry to compress video. H.264 codec standard developed by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG). Audio-video coding standard (AVS) is a working group of audio and video coding standard in China. VC-2, also known as Dirac Pro developed by BBC, is a royalty free technology that anyone can use and has been standardized through the SMPTE as VC-2. H.264 AVC, Dirac Pro, Dirac and AVS-P2 are dedicated to High Definition Video, while AVS-P7 is to mobile video. Out of many standards, this work performs a comparative analysis for the H.264 AVC, DIRAC PRO/SMPTE-VC-2 and AVS-P7 standards in low bitrate region and high bitrate region. Bitrate control and constant QP are the methods which are employed for analysis. Evaluation parameters like Compression Ratio, PSNR and SSIM are used for quality comparison. Depending on target application and available bitrate, order of performance is mentioned to show the preferred codec.

The current trend of digital convergence creates the need for the video encoder and decoder system, known as codec in short, that should support multiple video standards on a single platform. In a modern video codec, quantization is a key unit used for video compression. In this thesis, a generalized quantization algorithm and hardware implementation is presented to compute quantized coefficient for six different video codecs including the new developing codec High Efficiency Video Coding (HEVC). HEVC, successor to H.264/MPEG-4 AVC, aims to substantially improve coding efficiency compared to AVC High Profile. The thesis presents a high performance circuit shared architecture that can perform the quantization operation for HEVC, H.264/AVC, AVS, VC-1, MPEG- 2/4 and Motion JPEG (MJPEG). Since HEVC is still in drafting stage, the architecture was designed in such a way that any final changes can be accommodated into the design. The proposed quantizer architecture is completely division free as the division operation is replaced by multiplication, shift and addition operations. The design was implemented on FPGA and later synthesized in CMOS 0.18 μm technology. The results show that the proposed design satisfies the requirement of all codecs with a maximum decoding capability of 60 fps at 187.3 MHz for Xilinx Virtex4 LX60 FPGA of a 1080p HD video. The scheme is also suitable for low-cost implementation in modern multi-codec systems.