Letteratura scientifica selezionata sul tema "Tache focale"

«J’vais bien, j’suis pas malade !», disent-ils fièrement, droit dans les yeux, comme s’il fallait déplacer la mire, ou changer de focale… Santé : «État de bien-être physique, psychique et social», dit l’OMS. Sans doute, la parole se gagne-t-elle, c’est l’un des objets de la consultation proposée aux jeunes des Bosquets de Montfermeil, ou du Bois-du-Temple, de la Forestière, du Chêne Pointu, autres appellations bucoliques de quartiers de Clichy-sous-Bois. Voilà donc ce qui peut être observé, et donc dit, au Point Santé de la mission locale, après cinq années d’exercice.

A 58-year-old male patient presented with advanced hepatocellular carcinoma underwent transarterial chemoembolization (TACE) for hepatic focal lesions followed by TACE for a solitary hilar nodal metastasis combined with regorafenib therapy. One month later, the patient developed progressive jaundice. Work-up showed obstructive jaundice with intrahepatic biliary radicles dilatation. The diagnosis and treatment was achieved by combining endoscopic retrograde cholangiopancreatography and endoscopic ultrasonography and showed uncommon cause of obstructive jaundice due to common bile duct compression by a choledocho-nodal fistula following TACE of a metastatic hilar lymph node.

A short ischemic event (ischemic preconditioning (IPC)) can result in subsequent resistance to severe ischemic injury (ischemic tolerance (IT)). The expression and neuroprotective role of tumor necrosis factor (TNF- α) have been described in models of IPC and we have showed the participation of its processing enzyme, the TNF- α convertase enzyme (TACE) in this process. We have now decided to explore the expression and localization of TNF receptors (TNFR) as well as other signalling mechanisms involved in IT. A period of 10 mins of temporary middle cerebral artery occlusion (tMCAO) was used for focal IPC. To evaluate the ability of IPC to produce IT, permanent MCAO was performed 48 hours after IPC. Ischemic preconditioning produced a reduction in infarct volume, as we showed previously. Ischemic preconditioning caused upregulation of neuronal TNFR1 that was reduced by the selective TACE inhibitor BB1101. Intracerebral administration of TNFR1 antisense oligodeoxynucleotide, which caused a reduction in TNFR1 expression, inhibited the IPC-induced protective effect, showing that TNFR1 upregulation is implicated in IT. Moreover, treatment with BB1101, TNFR1 antisense and lactacystin—a specific proteasome inhibitor—blocked IPC-induced NF- κB. Immunohistochemical studies showed the expression of TACE and TNFR1 in neurons. In summary, these data show that IPC produces neuronal upregulation of TACE and TNFR1, and that the pathway TACE/TNF- α/TNFR1/NF- κB is involved in IT.

106 Background: The objective of this work was to develop recommendations for the organization and delivery of focal tumor ablation services. New, minimally-invasive ablation technologies such as radiofrequency ablation (RFA), microwave ablation (MWA), and transcatheter arterial chemoembolization (TACE) offer treatment options for patients with a variety of cancers. These emerging therapies can improve patient care (minimize side-effects, offer more rapid recovery with comparable or enhanced outcomes) compared to traditional approaches. However, they are often resource intensive, necessitating a planned system-level approach to ensure appropriate access to high quality services while optimizing care and resource utilization. Methods: This work was led by an Advisory Committee with regional, clinical, administrative and patient representatives and was based on best available evidence, current practice in Ontario, Canada, and guidance from other jurisdictions and experts in the field. A variety of data sources (clinical, system, provider), consultation with external stakeholders and consensus building supported the final recommendations. Results: Thirteen recommendations were developed. Clinical criteria are detailed for RFA for liver, kidney and lung tumors and TACE for hepatocellular carcinoma. MWA is not recommended for lung, liver or kidney tumors. System recommendations include infrastructure (capital equipment, multidisciplinary management and case conference review), the importance of volume-related expertise, and oversight for funding and collaborative planning. Results were broadly disseminated through 12 stakeholder groups connecting with over 40,000 individuals. Conclusions: A systematic approach to understanding opportunities and challenges for focal tumor ablation therapies resulted in multi-level recommendations spanning clinical criteria through to quality oversight. These recommendations will support improvements in care delivery in daily practice and at the system level.

Contrast enhancement at the margins/rim of embolization areas in hepatocellular-carcinoma (HCC) lesions treated with transarterial chemoembolization (TACE) might be an early prognostic indicator for HCC recurrence. The aim of this study was to evaluate the predictive value of rim perfusion for TACE recurrence as determined by perfusion CT (PCT). A total of 52 patients (65.6 ± 9.3 years) underwent PCT directly before, immediately after (within 48 h) and at follow-up (95.3 ± 12.5 days) after TACE. Arterial-liver perfusion (ALP), portal-venous perfusion (PVP) and hepatic-perfusion index (HPI) were evaluated in normal liver parenchyma, and on the embolization rim as well as the tumor bed. A total of 42 lesions were successfully treated, and PCT measurements showed no residually vascularized tumor areas. Embolization was not entirely successful in 10 patients with remaining arterialized focal nodular areas (ALP 34.7 ± 10.1 vs. 4.4 ± 5.3 mL/100 mL/min, p < 0.0001). Perfusion values at the TACE rim were lower in responders compared to normal adjacent liver parenchyma and edges of incompletely embolized tumors (ALP liver 16.3 ± 10.1 mL/100 mL/min, rim responder 8.8 ± 8.7 mL/100 mL/min, rim non-responder 23.4 ± 8.6 mL/100 mL/min, p = 0.005). At follow-up, local tumor relapse was observed in 17/42, and 15/42 showed no recurrence (ALP 39.1 ± 10.1 mL/100 mL/min vs. 10.0 ± 7.4 mL/100 mL/min, p = 0.0008); four patients had de novo disseminated disease and six patients were lost in follow-up. Rim perfusion was lower compared to adjacent recurring HCC and not different between groups. HCC lesions showed no rim perfusion after TACE, neither immediately after nor at follow-up at three months, both for mid-term responders and mid-term relapsing HCCs, indicating that rim enhancement is not a sign of reactive hyperemia and not predictive of early HCC recurrence.

Hepatocellular carcinoma (HCC) is a common malignancy worldwide. HCC-related mortality is high because most cases are diagnosed at an advanced stage. HCCs are relatively resistant to radiation and the liver is unable to tolerate the radiation doses required to achieve tumoricidal effects by standard external-beam radiation. Focal radiation techniques employing a 3D approach have been shown to safely permit higher levels of radiation to targeted regions within the liver. Delivery of therapy through hepatic artery branches preferentially affects HCC tumors and spares the surrounding liver parenchyma. Selective targeting of radionuclides to tumors has been shown to achieve high radiation dose ratios. Transarterial radionuclide therapies have been developed with the objective of achieving selective intra-arterial delivery of radiotherapy, including radioactive iodine-131 (131I), rhenium-188 (188Re), yttrium-90 (90Y) (resin or glass microspheres), and others. These treatments have been used to treat HCC via a selective transarterial approach as an alternative to TACE. Portal vein thrombosis (PVT) is a relative contraindication to transarterial chemoembolization (TACE); in contrast, high specific activity radiomicrospheres do not occlude a significant portion of the hepatic arterial vascular bed and can therefore be used in patients with PVT. The devices, toxicities, and results with use of the available radioembolic devices are reviewed in this article.

La performance des cibles du Laser LMJ est très sensible à l'uniformité de la tache focale du laser. La technique utilisée à ce jour pour éviter les inhomogénéités est de rendre le faisceau partiellement incohérent, ce qui a pour conséquence la fluctuation de points chauds (speckles) au cours du temps, avec un effet de moyenne. De nombreux travaux ont d'ores et déjà été menés concernant l'étude de ces points chauds dans le cadre d'un faisceau unique au plan focal. Dans cette thèse, on s'intéresse à ces points chauds lorsqu'il sont issus de la superposition de faisceaux multiples, et plus particulièrement aux points chauds dans le cas de la configuration du LMJ. On a établi une équation analytique permettant de calculer la taille des points chauds dans le cas d'un speckle généré par des faisceaux multiples. Cette formule est en parfait accord avec les différents résultats obtenus par simulations numériques grâce au code PARAX. On a ainsi pu prédire la taille du grain de speckle LMJ en fonction de différentes configurations LMJ telle qu'une configuration à deux ou trois cônes et pour des choix de polarisations différents. Il en ressort que l'impact de la polarisation est assez faible sur les caractéristiques du speckle LMJ. Toutefois la double polarisation est la plus adaptée aux critères d'uniformité requis pour une bonne interaction laser-plasma. D'autre part on a montré que les grains de speckle LMJ sont de l'ordre de la longueur d'onde.Dans la seconde partie de cette thèse, on a établi les formules des contraste, temps de vie, trajectoires et vitesses des points chauds deux techniques de lissage : Lissage par Dispersion Spectrale Transverse (LDST) et Longitudinal (LDSL). Ces derniers sont respectivement utilisés sur le NIF et prochainement sur le LMJ. On a ainsi montré que quels que soient le nombre de cône et le choix des polarisations faites sur le LMJ, la durée de vie d'un point chaud LMJ est environ de 2 ps et le contraste intégré sur des temps infinis est approximativement de 15%. Les vitesses sont également très faibles (10-6c) et faiblement influencées par le choix des polarisations
The future French Laser Megajoule (LMJ) is a multiple laser beam facility built to achieve Inertial confinement Fusion (ICF). It is mainly designed for an indirect drive scheme using X-rays conversion. In this scheme, the target in the center of the hohlraum is irradiated and then compressed by the X-rays more uniformly than what it would be in a direct drive schemes. However, a high of uniformity is still needed to reach ignition since the propagation of intense laser beams in an under-critical plasma can generate laser-plasma instabilities (LPI). The control of LPI is of crucial importance for the success of ICF. By breaking both spatial and temporal coherences, the use of optical smoothing techniques, such as smoothing by spectral dispersion (SSD), often dramatically reduces LPI and also ensures the reproducibility of laser conditions from one shot to another. An accurate description of the speckle pattern in the hohlraum is thus of great interest for ICF experiments.We focus our attention on the spatial and then temporal properties of the speckles pattern generated by multiple laser beams. At first, we establish equations for the 3D speckle size based on autocorrelation functions. Numerical simulations of the propagation of multiple laser beams in vacuum are then performed with the PARAX code in configurations where the paraxial approximation can be used. The case of speckle patterns in the LMJ configuration in the zone where all the beams overlap is eventually studied. We show that such speckles have an ellipsoidal shape. Finally, influence of the polarization of the beams on the shape, size and abundance of the speckles is also investigated. In a second part we study the important aspect of temporal smoothing techniques like the movement of the speckles. This work is also triggered by the development of a statistical model that describes the motion of hot spots in order to evaluate the contrast, the trajectory and the velocity of LMJ hot spots. We address these quantities in the case of a speckle pattern generated by multiple laser beams thanks to the autocorrelation function in intensity

La localisation et la caractérisation des événements sismiques sont essentielles pour comprendre l'origine des événements. Une fois l'origine des évènements et leur localisation déterminés, il est possible de déterminer le niveau de risque sismique dans certaines régions ou encore de comprendre l'impact de l'activité humaine. Il existe de nombreuses méthodes pour localiser les événements et elles utilisent les enregistrements sismiques (i.e., sismogrammes). Elles se basent soit sur les temps d'arrivées soit sur une partie ou la totalité du signal. Dans cette thèse, nous nous intéressons à une méthode en particulier qui est le renversement temporel ou textit{time reversal}. C'est une méthode qui utilise la totalité du signal enregistré. Le principe est de rétropropager les signaux renversés temporellement, les ondes ainsi générées vont venir former une tache à la position de la source appelée tache focale. Le renversement temporel a des conditions d'application spécifique i) les récepteurs doivent former une surface fermée appelée miroir ii) celui ne doit pas impacter le trajet des ondes iii) le modèle de vitesse doit être connu iv) le milieu est non atténuant. Dans cette thèse, nous nous intéressons d'abord à l'interprétation théorique de la tache focale c'est-à-dire à son sens physique. Pour cela, nous nous sommes appuyés sur un code de simulation d'onde existant (SPECFEM2D) et sur la théorie de l'homogénéisation du point source. Nous avons montré mathématiquement et numériquement sur plusieurs exemples que la tache focale est une somme de deux points-sources homogénéisés. Ce résultat est la contribution principale de cette thèse et ouvre une perspective majeure qui est de déterminer les paramètres de la source en faisant un nouveau problème inverse avec comme données la tache focale. Cependant les conditions du renversement temporel rendent son application dans des cas pratiques difficiles, surtout le besoin d'un miroir fermé. Nous avons donc essayé de quantifier l'impact d'un miroir incomplet sur le renversement temporel en gardant en tête l'idée de l'application. Pour cela nous nous sommes placés dans un cas géologiquement réaliste : le champ de gaz de Groningen. Les résultats ont montré que le miroir incomplet a un impact important sur la simulation, mais dans tous les cas une tache focale plus ou moins déformée est obtenue. De plus, nous nous illustrons l'impact positif des hétérogénéités sur la reconstruction du champ d'onde par renversement temporel. Ces résultats ouvrent des perspectives sur l'intégration des données de surface pour améliorer la reconstruction du champ d'onde quand le miroir est incomplet ou encore sur la complétion du miroir
The localization and the characterization of seismic events are essential to understand the origin of the earthquake. Once it has been determined, it is possible to generate maps of seismic risks of different areas and also to understand the impact of human activities. Several ways exist to locate seismic events, they use seismic recordings (i.e., seismograms). In those recordings, some methods use the time arrivals of particular waves and other parts or the entire signal. In this thesis, we are interested in one method: time reversal. This method used the entire signal. The principle is to backpropagate the recordings reversed in time. The generated waves focus on the source location and create a focal spot. The time reversal has four terms of application i) the receivers form a closed surface, called time reversal mirror, ii) the time reversal mirror does not perturb the wave propagation, iii) the medium is well known. Errors on the velocity model or interface positions would generate modifications in the wave path as compared to the path in the forward process, iv) the anelasticity is negligible. Anelastic attenuation would make a first-order time derivative appear in the wave equation so that the time reversibility would not be verified. In this thesis, we are first interested in the theoretical interpretation of the focal spot, that is to say in its physical meaning. To do so, we have used an existing software of wave propagation (SPECFEM2D) and we lean on the theory of point source homogenization. We have shown mathematically and numerically in several examples that the focal spot is a sum of the displacement generated by two homogenized point sources. This result is the main contribution of the thesis and opens a significant perspective which is to determine the source parameters by doing an inverse problem with the focal spot as the input data. However, the conditions of time reversal make its application difficult in practical cases. It is almost impossible to have a close mirror of receivers. We have tried to quantify the impact of an incomplete mirror on time reversal simulation. To do so, we use a realistic geological case: the Groningen gas field. The results show that the incomplete mirror has a huge impact on the time reversal wavefield but in every case, we tested, a focal spot is obtained. The focal spots are in these cases deformed. Therefore, we illustrate the positive impact of the heterogeneities on the wavefield reconstruction. These results open multiple perspectives such as the integration of surface data to improve the wavefield reconstruction when the mirror is open or such as the completion of the mirror

Dans le contexte de la fusion par confinement inertiel (FCI), le lissage optique est une technique utilisée pour obtenir une irradiation laser aussi homogène que possible, en modifiant les propriétés de cohérence temporelle et spatiale des faisceaux laser. L'utilisation du lissage optique est une nécessité sur les lasers de puissance comme le Laser MégaJoule (LMJ) pour limiter le développement des instabilités paramétriques issues de l'intéraction laser-plasma, et parmi elles, la rétrodiffusion Brillouin stimulée (RBS). Ces instabilités entraînent des défauts d'irradiation sur cible et peuvent aussi être une source d'endommagement dans la chaîne optique. Cependant ces techniques peuvent entraîner d'autres problèmes au niveau de la chaîne laser, tels que la conversion de modulation de phase en modulation d'amplitude (FM-AM), néfastes au bon déroulement des expériences et pouvant également endommager les chaînes laser.On comprend donc qu'il est nécessaire de trouver un compromis autour du lissage optique. L’évolution du compromis du lissage est cependant compliquée car la quantification des gains et des pertes est très difficile à établir. Ainsi, tant que la quantification n’est pas faite, le compromis n’évolue pas : le lasériste souhaite toujours moins de lissage et « l’expérimentateur » toujours plus de lissage mais aucun des deux ne peut apporter suffisamment d’éléments quantitatifs pour faire pencher la balance. Cette thèse propose donc de poser les premières briques permettant d'arriver à ce compromis pour le LMJ, à l'aide d'études théoriques et numériques.Nous comparons soigneusement le lissage longitudinal (LSSD) et transversal (TSSD) par dispersion spectrale dans une configuration de lissage idéale pour chaque cas. Avec des codes 3D, nous avons simulé la RBS dans un plasma d'or, typique des expériences de FCI et favorable au développement de la RBS. Nous montrons que, contrairement aux idées reçues, l'évolution temporelle de la RBS présente certaines différences entre les deux systèmes de lissage. Premièrement, les valeurs asymptotiques des niveaux de saturation ne sont pas tout à fait les mêmes. Avec une simple description des rayons et le calcul du gain RBS pour chaque rayon, nous avons pu expliquer cette différence. En outre, la dynamique de la RBS est également quelque peu différente. Nous avons montré que la dynamique RBS est déterminée par l'évolution temporelle des propriétés des surintensités et en particulier par la longueur d'interaction effective entre la lumière rétrodiffusée Brillouin et les points chauds. Cette longueur d'interaction effective dépend à la fois de la vitesse longitudinale et de la longueur des points chauds. En effet, la synchronisation des longueurs d'interaction effectives des deux schémas de lissage synchronise également la croissance des courbes de rétrodiffusion avant saturation.Nous montrons, également qu'il est possible de faire évoluer les paramètres de lissage du LMJ en illustrant une nouvelle façon de réduire la conversion FM-AM inévitablement présente dans les lasers de forte puissance. En répartissant le spectre total habituellement utilisé par un quadruplet (regroupement de 4 faisceaux), en deux parties de spectres identiques plus petits sur les faisceaux de gauche et de droite, la conversion FM en AM est considérablement réduite de 30% à 5% tout en maintenant la performance de lissage pour la RBS. Nous avons également montré que le temps de cohérence qui en résulte n'a aucun effet sur le niveau maximal de RBS atteint. De la même façon, il faudra étudier l'impact de ces évolutions sur d'autres instabilités telles que le diffusion Raman stimulée ou le transfert d'énergie par croisement de faisceaux
In the context of inertial confinement fusion (ICF), optical smoothing is a technique used to obtain the most homogeneous laser irradiation possible, by modifying the temporal and spatial coherence properties of the laser beams. The use of optical smoothing is a necessity on high-power lasers such as the Laser Mégajoule (LMJ) to limit the development of parametric instabilities resulting from laser-plasma interaction, and among them, stimulated Brillouin backscattering (SBS). These instabilities lead to target irradiation defects and can also be a source of damage in the optical lines. However, these techniques can lead to other problems in the laser lines, such as the conversion of phase modulation to amplitude modulation (FM-to-AM), which is harmful to the proper conduct of the experiments and can also damage the laser optics.It is therefore a necessity to find a compromise around optical smoothing. The evolution of the smoothing compromise is however complicated because the quantification of gains and losses is very difficult to establish. Thus, as long as quantification is not done, the compromise does not evolve: the laserist always wants less smoothing and the experimentalist always more smoothing, but neither of them can bring enough quantitative elements to tip the balance. This thesis therefore proposes to lay the first groundwork for reaching this compromise for the LMJ, using theoretical and numerical studies.We carefully compare longitudinal (LSSD) and transverse (TSSD) smoothing by spectral dispersion in an ideal smoothing configuration for each case. With 3D codes, we simulated SBS in a gold plasma, typical of ICF experiments and favourable to the development of SBS. We show that, contrary to popular belief, the temporal evolution of SBS shows some differences between the two smoothing schemes. First, the asymptotic values of saturation levels are not quite the same. With a simple description using light rays and the calculation of the SBS gain for each ray, we were able to explain this difference. In addition, the dynamics of SBS are also somewhat different. We have shown that the SBS dynamics is determined by the temporal evolution of the properties of the hot-spots and in particular by the effective interaction length between the Brillouin backscattered light and the hot-spots. This effective interaction length depends on both the longitudinal velocity and the length of the hot-spots. Indeed, the synchronization of the effective interaction lengths of the two smoothing schemes also synchronizes the growth of the backscatter curves before saturation.We also show that it is possible to change the smoothing parameters of the LMJ by illustrating a new way to reduce the FM-to-AM conversion inevitably present in high-power lasers. By splitting the total spectrum usually used by a quadruplet (grouping of 4 beams) into two parts of smaller identical spectra on the left and right beams, the FM-to-AM conversion is significantly reduced from 30% to 5% while maintaining the smoothing performance for SBS. We have also shown that the resulting coherence time of the laser has no effect on the maximum level of SBS achieved. Similarly, the impact of these developments on other instabilities such as stimulated Raman scattering or crossed beam energy transfer will also need to be investigated