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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Penumbra

Brizendine, Elizabeth Katherine 08 1900 (has links)
This thesis consists of a collection of poems. The poems entail a discussion of the weight of human decisions with regards to gender, sexuality, music, religion, and environment. A great deal of these pieces are in conversation with a type of death or an eclipsed ending in order to examine the outcome of each varied individual response to mortality.
12

THE INFLUENCE OF MACHINE MODEL AND OPTIMIZATION PARAMETERS ON THE GENERATION OF NARROW SEGMENTS IN STEP AND SHOOT INTENSITY MODULATED RADIOTHERAPY PLANS FOR SIMPLIFIED GEOMETRIES

Motmaen, Dadgar Maryam 10 1900 (has links)
<p>Generation of narrow segments is a matter of concern in step-and-shoot intensity modulated radiotherapy for several reasons. The measurement, calculation and delivery of dose from narrow segments may be complicated due to: the dosimetric properties of the detector; the effect of beam penumbra and heterogeneities within the patient; and the requirement for high geometric delivery precision respectively. The main purpose of this thesis was to investigate the parameters affecting the generation of narrow beam segments in IMRT optimization. Parameters such as effective source size, Gaussian height and width, density of the target volume, and gap between the tumor and normal tissue were varied to determine their influence on the number of narrow leaf pair separations. The gradient and penumbra were also examined. Two simple geometric models (thick model and thin model) with different dimensions were used. In the thick model, two 6-MV photon beams were incident on the target at right angles. A rectangular target was centered in a phantom with dimensions 20.25 cm×5.25 cm×20.25 cm. In the thin model, one 6-MV photon beam was normally incident on a 20.25 cm×1.25 cm×20.25 cm slab phantom. The relationship between the penumbra and number of narrow separated leaf pairs were examined for the thick model. The results did not show a consistent pattern. For the thin model, creating a gap between the target and the OAR decreased the total number of narrowly separated leaf pairs along the interface but increased the average dose delivered to the OAR. By varying the OAR max dose or the gap between the target and OAR, a peak was created in the dose profiles to compensate the penumbra. As gradient increased the peak height increased to compensate the dose fall-off. The width of the peak at half maximum changed with gradient but not in a predictable fashion.</p> / Master of Science (MSc)
13

Highly Physical Solar Radiation Pressure Modeling During Penumbra Transitions

Robertson, Robert Voorhies 09 June 2015 (has links)
Solar radiation pressure (SRP) is one of the major non-gravitational forces acting on spacecraft. Acceleration by radiation pressure depends on the radiation flux; on spacecraft shape, attitude, and mass; and on the optical properties of the spacecraft surfaces. Precise modeling of SRP is needed for dynamic satellite orbit determination, space mission design and control, and processing of data from space-based science instruments. During Earth penumbra transitions, sunlight is passing through Earth's lower atmosphere and, in the process, its path, intensity, spectral composition, and shape are significantly affected. This dissertation presents a new method for highly physical SRP modeling in Earth's penumbra called Solar radiation pressure with Oblateness and Lower Atmospheric Absorption, Refraction, and Scattering (SOLAARS). The fundamental geometry and approach mirrors past work, where the solar radiation field is modeled using a number of light rays, rather than treating the Sun as a single point source. This dissertation aims to clarify this approach, simplify its implementation, and model previously overlooked factors. The complex geometries involved in modeling penumbra solar radiation fields are described in a more intuitive and complete way to simplify implementation. Atmospheric effects due to solar radiation passing through the troposphere and stratosphere are modeled, and the results are tabulated to significantly reduce computational cost. SOLAARS includes new, more efficient and accurate approaches to modeling atmospheric effects which allow us to consider the spatial and temporal variability in lower atmospheric conditions. A new approach to modeling the influence of Earth's polar flattening draws on past work to provide a relatively simple but accurate method for this important effect. Previous penumbra SRP models tend to lie at two extremes of complexity and computational cost, and so the significant improvement in accuracy provided by the complex models has often been lost in the interest of convenience and efficiency. This dissertation presents a simple model which provides an accurate alternative to the full, high precision SOLAARS model with reduced complexity and computational cost. This simpler method is based on curve fitting to results of the full SOLAARS model and is called SOLAARS Curve Fit (SOLAARS-CF). Both the high precision SOLAARS model and the simpler SOLAARS-CF model are applied to the Gravity Recovery and Climate Experiment (GRACE) satellites. Modeling results are compared to the sub-nm/s^2 precision GRACE accelerometer data and the results of a traditional penumbra SRP model. These comparisons illustrate the improved accuracy of the SOLAARS and SOLAARS-CF models. A sensitivity analyses for the GRACE orbit illustrates the significance of various input parameters and features of the SOLAARS model on results. The SOLAARS-CF model is applied to a study of penumbra SRP and the Earth flyby anomaly. Beyond the value of its results to the scientific community, this study provides an application example where the computational efficiency of the simplified SOLAARS-CF model is necessary. The Earth flyby anomaly is an open question in orbit determination which has gone unsolved for over 20 years. This study quantifies the influence of penumbra SRP modeling errors on the observed anomalies from the Galileo, Cassini, and Rosetta Earth flybys. The results of this study prove that penumbra SRP is not an explanation for or significant contributor to the Earth flyby anomaly. / Ph. D.
14

Regeneration in the adult brain after focal cerebral ischemia : exploration of neurogenesis and angiogenesis

Jiang, Wei January 2006 (has links)
Background: Ischemic stroke ranks as the third major cause of clinical mortality and the leading cause of handicap in adults. Each year, stroke occurs in about 30,000 Swedes. The severity of an acute ischemic stroke depends mainly on the degree and duration of local cerebral blood flow (lCBF) reduction. Prompt reperfusion improves neurological deficits, spontaneous electrical activity, energy metabolism, cerebral protein synthesis (CPS), and tissue repair, among which cell proliferation (neurogenesis, gliosis) and revascularization (angiogenesis) may have important functional and therapeutic implications. Aims of the thesis: (1) To establish the photothrombotic ring stroke(PRS) model with late spontaneous reperfusion in adult mice; (2) To explore angiogenesis and neurogenesis in adult brain after focal cerebral ischemia. Materials and Methods: The PRS model in C57 BL adult mice and the middle cerebral artery suture occlusion (MCAO) model in adult Wistar rats were used. The 5-bromodeoxyuridine (BrdU) was delivered into animal after stroke induction to label DNA duplication. CBF, CPS and adenosine triphosphate (ATP) were measured by laser-Doppler flowmetry (LDF), [14C]–Iodoantipyrine and [3H]-Leucine double tracer autoradiography, and bioluminescence, respectively. Immunocytochemistry / immunofluoresence were performed to detect different proteins. The cell marker colocalization was analyzed by three-dimension (3-D) confocal. The cell counting was performed with a stereological counting system. Results: The PRS model was established in adult mice by irradiating the exposed skull with a 514.5 nm argon laser ring beam (3 mm diameter, 0.21 mm thick) at an intensity of 0.65 W/cm2 for 60s, with concurrent erythrosin B (4.25 mg/kg) intravenous infusion for 15s. The central cortical region within the ring locus was progressively encroached by an annular ring-shaped perfusion deficit, where lCBF LDF declined promptly to 43% of the baseline value at 30 min post irradiation. The lCBF-IAP amounted to 46-17-58 ml/100g/min, where CPS varied from 57-38-112% at 4h-48h-7days post ischemia. ATP declined at 4h, achieved its maximum level at 48h and was markedly reduced at 7 days postischemia. Morphologically, at 4h some neurons in the region at-risk appeared swollen, at 48h the majority were severely swollen, eosinophilic and pyknotic. Tissue morphology became partly restored at 7 days post stroke, when numerous cortical cells were immunolabeled by BrdU or the mitosis-specific marker phosphorylated histone H3 (Phos-H3). Some of these cells were even doubly immunopositive to the neuron-specific marker Neu N and the astrocyte marker GFAP, as analyzed by 3-D confocal. In adult rats exposed to MCAO, widespread BrdU-immunolabeled cells appeared in the cortex, ipsilateral striatum and dentate gyrus of the hippocampus. Some of which were doubleimmunolabeled by the neuron specific markers Map-2, β-tubulin III and Neu N as analyzed by 3-D confocal. As early as 24h postischemia, BrdU-immunopositive endothelial cells were aligned as microvessels, some of which exhibited distinguishable lumens in the ischemic boundary zone, where VEGF-A, B, C proteins and their receptors flt-1, fik-1, flt-4 were overexpressed at 72h after MCAO. Conclusion: PRS model in adult mice elicits a dynamic deterioration and then restoration of local CBF, CPS, ATP and tissue morphology in the spontaneously reperfused cerebral cortex at 7d after stroke, where cortical neurogenesis and gliosis occurred. In adult rats with MCAO, neurogenesis occurred at 30 and 60d in the penumbral cortex and striatum. Angiogenesis occurred as early as 24h, which contributed to the spontaneous reperfusion frequently observed in this setting of acute ischemic stroke.
15

Evolution des lésions ischémiques aiguës en IRM de diffusion / Evolution of acute ischemic diffusion-weighted lesions

Tisserand, Marie 30 September 2015 (has links)
Après traitement d’un AIC par thrombolyse, les lésions ischémiques en diffusion peuvent être réversibles, stables et/ou progresser. Cette thèse a pour objectif d’étudier en IRM ces phénomènes de réversibilité et de progression, de mieux comprendre leur physiopathologie, et d’appréhender le rôle pronostic du volume des lésions en diffusion. La réversibilité en diffusion a été rapportée après recanalisation artérielle, chez l’animal et chez l’homme. Dans notre cohorte de 155 patients, nous avons étudié ce phénomène par une analyse voxel à voxel sur des IRM avant et 24h après thrombolyse. Nous avons montré que la réversibilité des anomalies en diffusion à 24h était fréquente et surtout persistait sur une IRM plus tardive (médiane 54h) pour plus de 70% des voxels [58.0-85.9], suggérant que ce phénomène n’était pas transitoire. De plus, seule la réversibilité permanente était associée à une amélioration neurologique à 24h (OR=1.15, CI95%[ 1.03-1.27], P=0.008 par mL). La substance blanche a été décrite comme plus résistante à l’ischémie sur des modèles murins. Chez l’homme, nous avons confirmé la prédominance en substance blanche des phénomènes de réversibilité, avec une probabilité de régression plus importante pour un voxel de substance blanche que pour un voxel de substance grise. Ces résultats pourraient aider à identifier avant décision thérapeutique les lésions potentiellement réversibles, c'est-à-dire celles prédominant en substance blanche. Même s’il existe une association entre le volume de lésion en diffusion avant traitement et le pronostic fonctionnel à 3 mois, la réversibilité des lésions pourrait remettre en cause les seuils de volume au-delà desquels une revascularisation pourrait être futile. En effet, en limitant la progression des anomalies en diffusion et en favorisant leur régression, la revascularisation pourrait aussi avoir un impact sur le pronostic fonctionnel des patients avec un large volume lésionnel (≥70mL). Dans une population de 267 patients avec un infarctus de l’artère cérébrale moyenne traités par thrombolyse, 54 avaient un volume en diffusion ≥70mL, dont 12(22%) avaient un pronostic fonctionnel favorable à 3 mois. L’odds-ratio de la recanalisation pour le pronostic fonctionnel favorable dans le groupe ≥70mL était de 4.87 [1.15-20.73], P=0.03 en faveur d’un impact positif de la recanalisation même dans ce groupe. En l’absence de reperfusion, les anomalies en diffusion progressent au sein de la pénombre ischémique. Selon le modèle « core/pénombre », cette progression lésionnelle ne doit pas s’accompagner d’une aggravation neurologique. Nous avons formulé l’hypothèse que si elle survenait au-delà de la pénombre (dans des zones asymptomatiques), elle s’accompagnerait d’une détérioration neurologique. La détérioration neurologique précoce non expliquée (absence de transformation hémorragique, d’œdème malin ou d’autre cause identifiable) est observée chez 7% de nos 309 patients thrombolysés. Nous avons validé l’hypothèse initiale d’une progression des anomalies en diffusion au-delà de la pénombre chez ces patients. Par une analyse voxel à voxel, elle était présente chez 9 cas/10 (7-137mL; > 10mL chez 8 cas), et son volume était significativement supérieur à celui des 30 contrôles sans détérioration précoce (P=0.047). De plus, sa topographie était congruente avec les fonctions neurologiques qui s’étaient détériorées. L’ensemble de ces résultats participe à une meilleure compréhension de l’évolution des lésions ischémiques aiguës en IRM de diffusion et offre des perspectives pour adapter la prise en charge individuelle afin d’améliorer le pronostic fonctionnel. / Within the first 24 hours after IV-rtPA, diffusion-weighted ischemic lesions can reverse, remain stable or grow. The aim of this thesis is to study these reversal and growth phenomena, to better understand their pathophysiology and to gain insight into the prognostic value of diffusion lesion volume. Diffusion lesion reversal was reported in animals and humans after arterial recanalization. In our sample of 155 patients, we studied this phenomenon with MRI performed before and 24 hours after thrombolysis using a voxel-based approach. First, we demonstrated that 24 hours diffusion reversal was frequent and sustained on a late MRI (median 54h) for over two-thirds of the voxels. Second, sustained reversal was associated with 24hr neurological improvement (OR=1.15, IC95%[ 1.03-1.27], P=0.008 per 1mL). Animal studies have suggested that white matter is more resistant to ischemia than gray matter. In humans, we confirmed that diffusion lesion reversal was more frequent in white matter than in gray matter and disclosed that white matter voxels were more prone to reverse than gray matter voxels. The amount of white matter in the initial diffusion lesion may therefore be a significant determinant of reversibility. Large diffusion lesion volume is associated with poor outcome. However, revascularization therapy can prevent infarct growth or even promote lesion reversal. It is still unclear whether these treatments are beneficial in patients with large diffusion volumes (≥70mL). In our series including 267 patients with middle cerebral artery stroke treated with thrombolysis, 54 patients had a ≥70mL diffusion volume, of which 12(22%) had a 3 month favorable outcome. Odds-ratio of recanalization for favorable outcome in the ≥70mL group was 4.87 [1.15-20.73], P=0.03 supporting a benefit of recanalization in this subgroup. Diffusion lesions growth is usually located within the ischemic penumbra. We hypothesized that if it occurred beyond its boundaries, it would translate into neurological deterioration. Unexplained early neurological deterioration is frequent (70% of early neurological deteriorations, 7% in our series of 309 thrombolysed patients) and its causes are not well-known (no symptomatic intra cerebral hemorrhage, malignant edema or post-stroke seizure). We confirmed our hypothesis in these patients with diffusion growth beyond the penumbra. This growth occurred in 9 of the 10 studied patients (7-137mL; > 10mL in 8 patients) and it was significantly larger than in the 30 controls with early neurological deterioration (P=0.047). Moreover its topography matched the neurological items that deteriorated. All together, these results contribute to a better understanding of acute ischemic lesions using diffusion-weighted imaging and may offer perspectives to adapt individual patient care.
16

Evolution des lésions ischémiques aiguës en IRM de diffusion / Evolution of acute ischemic diffusion-weighted lesions

Tisserand, Marie 30 September 2015 (has links)
Après traitement d’un AIC par thrombolyse, les lésions ischémiques en diffusion peuvent être réversibles, stables et/ou progresser. Cette thèse a pour objectif d’étudier en IRM ces phénomènes de réversibilité et de progression, de mieux comprendre leur physiopathologie, et d’appréhender le rôle pronostic du volume des lésions en diffusion. La réversibilité en diffusion a été rapportée après recanalisation artérielle, chez l’animal et chez l’homme. Dans notre cohorte de 155 patients, nous avons étudié ce phénomène par une analyse voxel à voxel sur des IRM avant et 24h après thrombolyse. Nous avons montré que la réversibilité des anomalies en diffusion à 24h était fréquente et surtout persistait sur une IRM plus tardive (médiane 54h) pour plus de 70% des voxels [58.0-85.9], suggérant que ce phénomène n’était pas transitoire. De plus, seule la réversibilité permanente était associée à une amélioration neurologique à 24h (OR=1.15, CI95%[ 1.03-1.27], P=0.008 par mL). La substance blanche a été décrite comme plus résistante à l’ischémie sur des modèles murins. Chez l’homme, nous avons confirmé la prédominance en substance blanche des phénomènes de réversibilité, avec une probabilité de régression plus importante pour un voxel de substance blanche que pour un voxel de substance grise. Ces résultats pourraient aider à identifier avant décision thérapeutique les lésions potentiellement réversibles, c'est-à-dire celles prédominant en substance blanche. Même s’il existe une association entre le volume de lésion en diffusion avant traitement et le pronostic fonctionnel à 3 mois, la réversibilité des lésions pourrait remettre en cause les seuils de volume au-delà desquels une revascularisation pourrait être futile. En effet, en limitant la progression des anomalies en diffusion et en favorisant leur régression, la revascularisation pourrait aussi avoir un impact sur le pronostic fonctionnel des patients avec un large volume lésionnel (≥70mL). Dans une population de 267 patients avec un infarctus de l’artère cérébrale moyenne traités par thrombolyse, 54 avaient un volume en diffusion ≥70mL, dont 12(22%) avaient un pronostic fonctionnel favorable à 3 mois. L’odds-ratio de la recanalisation pour le pronostic fonctionnel favorable dans le groupe ≥70mL était de 4.87 [1.15-20.73], P=0.03 en faveur d’un impact positif de la recanalisation même dans ce groupe. En l’absence de reperfusion, les anomalies en diffusion progressent au sein de la pénombre ischémique. Selon le modèle « core/pénombre », cette progression lésionnelle ne doit pas s’accompagner d’une aggravation neurologique. Nous avons formulé l’hypothèse que si elle survenait au-delà de la pénombre (dans des zones asymptomatiques), elle s’accompagnerait d’une détérioration neurologique. La détérioration neurologique précoce non expliquée (absence de transformation hémorragique, d’œdème malin ou d’autre cause identifiable) est observée chez 7% de nos 309 patients thrombolysés. Nous avons validé l’hypothèse initiale d’une progression des anomalies en diffusion au-delà de la pénombre chez ces patients. Par une analyse voxel à voxel, elle était présente chez 9 cas/10 (7-137mL; > 10mL chez 8 cas), et son volume était significativement supérieur à celui des 30 contrôles sans détérioration précoce (P=0.047). De plus, sa topographie était congruente avec les fonctions neurologiques qui s’étaient détériorées. L’ensemble de ces résultats participe à une meilleure compréhension de l’évolution des lésions ischémiques aiguës en IRM de diffusion et offre des perspectives pour adapter la prise en charge individuelle afin d’améliorer le pronostic fonctionnel. / Within the first 24 hours after IV-rtPA, diffusion-weighted ischemic lesions can reverse, remain stable or grow. The aim of this thesis is to study these reversal and growth phenomena, to better understand their pathophysiology and to gain insight into the prognostic value of diffusion lesion volume. Diffusion lesion reversal was reported in animals and humans after arterial recanalization. In our sample of 155 patients, we studied this phenomenon with MRI performed before and 24 hours after thrombolysis using a voxel-based approach. First, we demonstrated that 24 hours diffusion reversal was frequent and sustained on a late MRI (median 54h) for over two-thirds of the voxels. Second, sustained reversal was associated with 24hr neurological improvement (OR=1.15, IC95%[ 1.03-1.27], P=0.008 per 1mL). Animal studies have suggested that white matter is more resistant to ischemia than gray matter. In humans, we confirmed that diffusion lesion reversal was more frequent in white matter than in gray matter and disclosed that white matter voxels were more prone to reverse than gray matter voxels. The amount of white matter in the initial diffusion lesion may therefore be a significant determinant of reversibility. Large diffusion lesion volume is associated with poor outcome. However, revascularization therapy can prevent infarct growth or even promote lesion reversal. It is still unclear whether these treatments are beneficial in patients with large diffusion volumes (≥70mL). In our series including 267 patients with middle cerebral artery stroke treated with thrombolysis, 54 patients had a ≥70mL diffusion volume, of which 12(22%) had a 3 month favorable outcome. Odds-ratio of recanalization for favorable outcome in the ≥70mL group was 4.87 [1.15-20.73], P=0.03 supporting a benefit of recanalization in this subgroup. Diffusion lesions growth is usually located within the ischemic penumbra. We hypothesized that if it occurred beyond its boundaries, it would translate into neurological deterioration. Unexplained early neurological deterioration is frequent (70% of early neurological deteriorations, 7% in our series of 309 thrombolysed patients) and its causes are not well-known (no symptomatic intra cerebral hemorrhage, malignant edema or post-stroke seizure). We confirmed our hypothesis in these patients with diffusion growth beyond the penumbra. This growth occurred in 9 of the 10 studied patients (7-137mL; > 10mL in 8 patients) and it was significantly larger than in the 30 controls with early neurological deterioration (P=0.047). Moreover its topography matched the neurological items that deteriorated. All together, these results contribute to a better understanding of acute ischemic lesions using diffusion-weighted imaging and may offer perspectives to adapt individual patient care.
17

Energy and intensity modulated radiation therapy with electrons

Olofsson, Lennart January 2005 (has links)
In recent years intensity modulated radiation therapy with photons (xIMRT) has gained attention due to its ability to reduce the dose in the tissues close to the tumour volume. However, this technique also results in a large low dose volume. Electron IMRT (eIMRT) has the potential to reduce the integral dose to the patient due to the dose fall off in the electron depth dose curves. This dose fall off makes it possible to modulate the dose distribution in the direction of the beam by selecting appropriate electron energies. The use of a computer based energy selection method was examined in combination with the IMRT technique to optimise the electron dose distribution. It is clearly illustrated that the energy optimisation procedure reduces the dose to lung and heart in a breast cancer treatment. To shape the multiple electron subfields (beamlets) that are used in eIMRT, an electron multi leaf collimator (eMLC) is needed. However, photons produced in a conventional electron treatment head could penetrate such an added eMLC, thus producing an undesirable dose contribution. The leakage levels normally achieved are acceptable for standard single electron field treatments but could become unacceptably high in eIMRT treatments where a lot of small subfields are combined. To limit this photon contribution, the photon MLC (xMLC) was used to shield off large parts of the photon leakage. The effect of this xMLC shielding on the reduction of photon leakage, the electron beam penumbras, and electron output (dose level), was studied using Monte Carlo methods for different electron treatment head designs. The use of helium as a mean to reduce the electron scatter in the treatment head, and thus the perturbating effect of the xMLC on electron beam penumbra and output, was also investigated. This thesis shows that the effect of the xMLC shielding on the electron beam penumbra and output can be made negligible while still obtaining a significantly reduced x-ray leakage dose contribution. The result is a large gain in radiation protection of the patient and a better dynamic range for the eIMRT dose optimisation. For this optimisation a computer based electron energy selection method was developed and tested on two clinical cases.
18

Le corps féminin et la tyrannie de la beauté dans Truismes de Marie Darrieussecq et Clara et la pénombre de José Carlos Somoza

Séguin, Marie-Hélène 02 1900 (has links) (PDF)
Notre mémoire porte sur la représentation du corps féminin dans deux œuvres littéraires : Truismes de Marie Darrieussecq (1996) et Clara et la pénombre de José Carlos Somoza (2003). À l'aide des théories féministes, nous tentons d'analyser ce que la beauté représente comme tyrannie pour les personnages féminins, qui doivent se plier aux standards esthétiques irréalistes imposés par la société dans laquelle ils évoluent. Ces normes correspondent à celles de la culture occidentale patriarcale actuelle, c'est-à-dire au corps construit, proche de l'objet artificiel. Dans cette optique, l'aspect naturel du corps est évacué; ce qui rappelle l'animalité est considéré comme laid. Le but de notre mémoire est de faire ressortir les similitudes et les différences entre les deux romans, qui proposent chacun une forme de matérialité différente : le corps animal et le corps-objet. Les études féministes ont montré que la femme a été reléguée à la matérialité en vertu de la dichotomie corps/esprit dans les conceptions judéo-chrétiennes. Dès lors, l'esthétique du corps est devenue pour elle un gage de valeur sociale. Fortement encouragée par la société à se plier aux critères de beauté, la femme doit livrer un combat perpétuel contre elle-même, physiquement et mentalement, afin d'y correspondre. Autrement; elle risque le rejet, le mépris et les mauvais traitements. Nous analysons donc le travail que les protagonistes font pour se conformer aux standards esthétiques et comment cette obligation d'être belle est aliénante pour elles. Nous constatons également qu'elles demeurent toutes deux marchandises, avec le manque de droits, de libertés et d'identité que cet état implique. Toutefois, elles résistent finalement à leur condition esthétique aliénante, en commençant par le refus de n'être que matérialité. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Corps, Femme, Beauté, Aliénation, Animal, Objet, Résistance, Truismes, Marie Darrieussecq, Clara et la pénombre, José Carlos Somoza
19

Evolution des lésions ischémiques aiguës en IRM de diffusion / Evolution of acute ischemic diffusion-weighted lesions

Tisserand, Marie 30 September 2015 (has links)
Après traitement d’un AIC par thrombolyse, les lésions ischémiques en diffusion peuvent être réversibles, stables et/ou progresser. Cette thèse a pour objectif d’étudier en IRM ces phénomènes de réversibilité et de progression, de mieux comprendre leur physiopathologie, et d’appréhender le rôle pronostic du volume des lésions en diffusion. La réversibilité en diffusion a été rapportée après recanalisation artérielle, chez l’animal et chez l’homme. Dans notre cohorte de 155 patients, nous avons étudié ce phénomène par une analyse voxel à voxel sur des IRM avant et 24h après thrombolyse. Nous avons montré que la réversibilité des anomalies en diffusion à 24h était fréquente et surtout persistait sur une IRM plus tardive (médiane 54h) pour plus de 70% des voxels [58.0-85.9], suggérant que ce phénomène n’était pas transitoire. De plus, seule la réversibilité permanente était associée à une amélioration neurologique à 24h (OR=1.15, CI95%[ 1.03-1.27], P=0.008 par mL). La substance blanche a été décrite comme plus résistante à l’ischémie sur des modèles murins. Chez l’homme, nous avons confirmé la prédominance en substance blanche des phénomènes de réversibilité, avec une probabilité de régression plus importante pour un voxel de substance blanche que pour un voxel de substance grise. Ces résultats pourraient aider à identifier avant décision thérapeutique les lésions potentiellement réversibles, c'est-à-dire celles prédominant en substance blanche. Même s’il existe une association entre le volume de lésion en diffusion avant traitement et le pronostic fonctionnel à 3 mois, la réversibilité des lésions pourrait remettre en cause les seuils de volume au-delà desquels une revascularisation pourrait être futile. En effet, en limitant la progression des anomalies en diffusion et en favorisant leur régression, la revascularisation pourrait aussi avoir un impact sur le pronostic fonctionnel des patients avec un large volume lésionnel (≥70mL). Dans une population de 267 patients avec un infarctus de l’artère cérébrale moyenne traités par thrombolyse, 54 avaient un volume en diffusion ≥70mL, dont 12(22%) avaient un pronostic fonctionnel favorable à 3 mois. L’odds-ratio de la recanalisation pour le pronostic fonctionnel favorable dans le groupe ≥70mL était de 4.87 [1.15-20.73], P=0.03 en faveur d’un impact positif de la recanalisation même dans ce groupe. En l’absence de reperfusion, les anomalies en diffusion progressent au sein de la pénombre ischémique. Selon le modèle « core/pénombre », cette progression lésionnelle ne doit pas s’accompagner d’une aggravation neurologique. Nous avons formulé l’hypothèse que si elle survenait au-delà de la pénombre (dans des zones asymptomatiques), elle s’accompagnerait d’une détérioration neurologique. La détérioration neurologique précoce non expliquée (absence de transformation hémorragique, d’œdème malin ou d’autre cause identifiable) est observée chez 7% de nos 309 patients thrombolysés. Nous avons validé l’hypothèse initiale d’une progression des anomalies en diffusion au-delà de la pénombre chez ces patients. Par une analyse voxel à voxel, elle était présente chez 9 cas/10 (7-137mL; > 10mL chez 8 cas), et son volume était significativement supérieur à celui des 30 contrôles sans détérioration précoce (P=0.047). De plus, sa topographie était congruente avec les fonctions neurologiques qui s’étaient détériorées. L’ensemble de ces résultats participe à une meilleure compréhension de l’évolution des lésions ischémiques aiguës en IRM de diffusion et offre des perspectives pour adapter la prise en charge individuelle afin d’améliorer le pronostic fonctionnel. / Within the first 24 hours after IV-rtPA, diffusion-weighted ischemic lesions can reverse, remain stable or grow. The aim of this thesis is to study these reversal and growth phenomena, to better understand their pathophysiology and to gain insight into the prognostic value of diffusion lesion volume. Diffusion lesion reversal was reported in animals and humans after arterial recanalization. In our sample of 155 patients, we studied this phenomenon with MRI performed before and 24 hours after thrombolysis using a voxel-based approach. First, we demonstrated that 24 hours diffusion reversal was frequent and sustained on a late MRI (median 54h) for over two-thirds of the voxels. Second, sustained reversal was associated with 24hr neurological improvement (OR=1.15, IC95%[ 1.03-1.27], P=0.008 per 1mL). Animal studies have suggested that white matter is more resistant to ischemia than gray matter. In humans, we confirmed that diffusion lesion reversal was more frequent in white matter than in gray matter and disclosed that white matter voxels were more prone to reverse than gray matter voxels. The amount of white matter in the initial diffusion lesion may therefore be a significant determinant of reversibility. Large diffusion lesion volume is associated with poor outcome. However, revascularization therapy can prevent infarct growth or even promote lesion reversal. It is still unclear whether these treatments are beneficial in patients with large diffusion volumes (≥70mL). In our series including 267 patients with middle cerebral artery stroke treated with thrombolysis, 54 patients had a ≥70mL diffusion volume, of which 12(22%) had a 3 month favorable outcome. Odds-ratio of recanalization for favorable outcome in the ≥70mL group was 4.87 [1.15-20.73], P=0.03 supporting a benefit of recanalization in this subgroup. Diffusion lesions growth is usually located within the ischemic penumbra. We hypothesized that if it occurred beyond its boundaries, it would translate into neurological deterioration. Unexplained early neurological deterioration is frequent (70% of early neurological deteriorations, 7% in our series of 309 thrombolysed patients) and its causes are not well-known (no symptomatic intra cerebral hemorrhage, malignant edema or post-stroke seizure). We confirmed our hypothesis in these patients with diffusion growth beyond the penumbra. This growth occurred in 9 of the 10 studied patients (7-137mL; > 10mL in 8 patients) and it was significantly larger than in the 30 controls with early neurological deterioration (P=0.047). Moreover its topography matched the neurological items that deteriorated. All together, these results contribute to a better understanding of acute ischemic lesions using diffusion-weighted imaging and may offer perspectives to adapt individual patient care.
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Law in 3-Dimensions

2013 March 1900 (has links)
This project, overall, involves a theory of law as dimensions. Throughout the history of the study of law, many different theoretical paradigms have emerged proffering different and competing ways to answer the question ‘what is law’? Traditionally, many of these paradigms have been at irreconcilable odds with one another. Notwithstanding this seeming reality, the goal of this project was to attempt to take three of the leading paradigms in legal theory and provide a way to explain how each might fit into a single coherent theory of law. I set out to accomplish this by drawing on the field of theoretical physics and that field’s use of spatial dimensions in explaining various physical phenomena. By engaging in a dimensional analysis of law, I found that I was able to place each paradigm within its own dimension with that dimension being defined by a specific element of time, and in doing so much of the conflict between the paradigms came to be ameliorated. The project has been divided into two main parts. PART I discusses the fundamentals of legal theory (Chapter 1) and the fundamentals of dimensions (Chapter 2). These fundamentals provide a foundation for a dimensional analysis of law which takes place throughout PART II. In Chapter 3, I argue that the three fundamental theses of Positivism coalesce with the 1st-dimension of law, which is defined as law as it exists at any one point in time. From there, I argue in Chapter 4 that the 2nd-dimension of law, being law as it exists between two points in time (i.e. when cases are adjudicated), is characterized by Pragmatism. I then turn, in Chapter 5, to argue that the 3rd-dimension of law, being law as it exists from the very first point in legal time to the ever changing present day, coalesces with the fundamental theses of Naturalism. Ultimately then, I argue that a theory of law as dimensions, through the vantage points of the specific elements of time, provides a more complete account of the nature of law.

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