Cerebral hemodynamics on MR perfusion images before and after bypass surgery in patients with giant intracranial aneurysms

Preoperative assessment of the anatomy and dynamics of cerebral circulation for patients with giant intracranial aneurysm can improve both outcome prediction and therapeutic approach. The aim of our study was to use perfusion MR imaging to evaluate cerebral hemodynamics in such patients before and after extraintracranial high-flow bypass surgery. METHODS: Five patients with a giant aneurysm of the intracranial internal carotid artery underwent MR studies before, 1 week after, and 1 month after high-flow bypass surgery. We performed MR and digital subtraction angiography, and conventional and functional MR sequences (diffusion and perfusion). Surgery consisted of middle cerebral artery (MCA)-internal carotid artery bypass with saphenous vein grafts (n = 4) or MCA-external carotid artery bypass (n = 1). RESULTS: In four patients, MR perfusion study showed impaired hemodynamics in the vascular territory supplied by the MCA of the aneurysm side, characterized by significantly reduced mean cerebral blood flow (CBF), whereas mean transit time (MTT) and regional cerebral blood volume (rCBV) were either preserved, reduced, or increased. After surgery, angiography showed good canalization of the bypass graft. MR perfusion data obtained after surgery showed improved cerebral hemodynamics in all cases, with a return of CBF index (CBFi), MTT, and rCBV to nearly normal values. CONCLUSION: Increased MTT with increased or preserved rCBV can be interpreted as a compensatory vasodilatory response to reduced perfusion pressure, presumably from compression and disturbed flow in the giant aneurysmal sac. When maximal vasodilation has occurred, however, the brain can no longer compensate for diminished perfusion by vasodilation, and rCBV and CBFi diminish. Bypass surgery improves hemodynamics, increasing perfusion pressure and, thus, CBFi. Perfusion MR imaging can be used to evaluate cerebral hemodynamics in patients with intracranial giant aneurysm.BACKGROUND AND PURPOSE: Preoperative assessment of the anatomy and dynamics of cerebral circulation for patients with giant intracranial aneurysm can improve both outcome prediction and therapeutic approach. The aim of our study was to use perfusion MR imaging to evaluate cerebral hemodynamics in such patients before and after extraintracranial high-flow bypass surgery. METHODS: Five patients with a giant aneurysm of the intracranial internal carotid artery underwent MR studies before, 1 week after, and 1 month after high-flow bypass surgery. We performed MR and digital subtraction angiography, and conventional and functional MR sequences (diffusion and perfusion). Surgery consisted of middle cerebral artery (MCA)-internal carotid artery bypass with saphenous vein grafts (n = 4) or MCA-external carotid artery bypass (n = 1). RESULTS: In four patients, MR perfusion study showed impaired hemodynamics in the vascular territory supplied by the MCA of the aneurysm side, characterized by significantly reduced mean cerebral blood flow (CBF), whereas mean transit time (MTT) and regional cerebral blood volume (rCBV) were either preserved, reduced, or increased. After surgery, angiography showed good canalization of the bypass graft. MR perfusion data obtained after surgery showed improved cerebral hemodynamics in all cases, with a return of CBF index (CBFi), MTT, and rCBV to nearly normal values. CONCLUSION: Increased MTT with increased or preserved rCBV can be interpreted as a compensatory vasodilatory response to reduced perfusion pressure, presumably from compression and disturbed flow in the giant aneurysmal sac. When maximal vasodilation has occurred, however, the brain can no longer compensate for diminished perfusion by vasodilation, and rCBV and CBFi diminish. Bypass surgery improves hemodynamics, increasing perfusion pressure and, thus, CBFi. Perfusion MR imaging can be used to evaluate cerebral hemodynamics in patients with intracranial giant aneurysm

Relationship between supratentorial arachnoid cyst and chronic subdural hematoma: neuroradiological evidence and surgical treatment.

Arachnoid cysts are relatively common congenital intracranial mass lesions that arise during the development of the meninges. They can be complicated by the formation of an ipsilateral chronic subdural hematoma (CSDH) after minor cranial trauma. Treatment of these coexisting conditions remains controversial. In this study the authors describe the anatomical, clinical, and neuroradiological features and outcome in a series of patients whose CSDH associated with arachnoid cysts were managed surgically by draining the hematoma alone and leaving the cyst intact. The authors based this surgical management on histological and neuroradiological observations concerning these associated medical conditions. A series of 8 patients with CSDHs associated with arachnoid cysts underwent surgery to drain the hematoma though a bur hole. The arachnoid cyst was left intact. Postoperative follow-up included CT scanning and T1- and T2-weighted MR imaging. Results. Clinical, anatomical, and radiological observations suggest that because separate membranes cover arachnoid cysts and the related hematoma, arachnoid cysts remain unaffected by the subdural bleeding. In the present study, these observations received support from the neuroimaging appearances, suggesting that arachnoid cysts related to hematoma contained only blood breakdown products from the hematoma that had filtered through the reciprocal dividing membranes

Resignificación política de los contextos urbanos. Redes de reproducción social compartida

[spa] Esta tesis se centra en el problema de la justicia urbana desde una perspectiva feminista que explora la reproducción social y atiende a cómo las experiencias sociales de las personas, en particular la forma en que experimentan la vulnerabilidad moldea sus percepciones y define la relación entre imaginarios comunitarios, utopías, deseos y la vida cotidiana. Estos cuatro elementos son fundamentales para entender los proyectos comunitarios de reapropiación de espacios y tiempos que he analizado a través de una metodología etnográfica. La noción de justicia urbana que se analiza en este trabajo nos permite identificar su alcance y sus limitaciones respecto a su carácter transformador y su resistencia a las dinámicas de la ciudad neoliberal. A partir de esta reflexión y de mi propia posición situada y crítica en el mundo, me propongo analizar las experiencias e imaginarios comunitarios y las utopías cotidianas en distintos barrios de grandes ciudades, vinculándolos con los conceptos de deseo y reproducción social desde las voces y vivencias de sus protagonistas. De esta manera, busco profundizar en la idea de justicia urbana que se trasluce en sus testimonios. El objetivo es desafiar la lógica del sistema simbólico-material heteropatriarcal y neoliberal, construyendo un discurso que reconozca la multiplicidad y la diferencia y la posibilidad real de crear espacios de convivencia liberadores que son ejemplos de justicia urbana. Para desarrollar un análisis crítico de los conceptos que sustentan esta investigación, situaré este estudio en el marco de la obra de Henri Lefebvre sobre el espaciotiempo urbano y el derecho a la ciudad, adoptando una perspectiva feminista que ponga atención a las necesidades y los cuidados. Exploraré los espacios-tiempos inesperados como un posible motor para la creación de utopías cotidianas, es decir, lugares donde lo utópico se entrelaza con lo ordinario, dando lugar a prácticas diarias innovadoras e imprevistas. Los cuerpos que transitan por estos espacios utópicos son los principales agentes de cambio social, gracias a las relaciones y experiencias que los exponen a una constante reeducación del deseo y el vínculo social. Estas relaciones, estructuradas en redes de reproducción social compartida, configuran nuestro mapa urbano cotidiano, lleno de experiencias transformadoras que desafían el paradigma económico-social dominante de la ciudad neoliberal. Para esta investigación, he analizado distintas experiencias comunitarias en barrios con distinto perfil sociodemográfico, en cada una de estas ciudades: Barcelona, Madrid y Roma. Estos lugares son ejemplos de espacios autogestionados y de actividades socioculturales que han surgido en y desde los márgenes. La elección de estos casos se debe a su historia de lucha, sus patrones migratorios, su composición de clases y la forma en que estos factores se relacionan con el territorio y la arquitectura de cada barrio. Mi trabajo se divide en dos partes principales: una revisión de archivos municipales y un trabajo de campo en el que observé los espacios autogestionados que surgieron a partir de procesos de reapropiación en cada uno de los barrios estudiados y a los que se refiere el análisis etnográfico. Mi conclusión es que necesitamos dar visibilidad a estas experiencias, auténticas utopías cotidianas, que confrontan con las dinámicas mercantilizadas de la gentrificación que son los auténticos obstáculos para la justicia urbana y la igualdad de género.[cat] Aquesta tesi es centra en el problema de la justícia urbana des d'una perspectiva feminista que explora la reproducció social i atén com les experiències socials de les persones, en particular la manera com experimenten la vulnerabilitat modela les seves percepcions i defineix la relació entre imaginaris comunitaris, utopies, desitjos i la vida quotidiana. Aquests quatre elements són fonamentals per entendre els projectes comunitaris de reapropiació d’espais i temps que he analitzat a través d'una metodologia etnogràfica. La noció de justícia urbana que s'analitza en aquest treball ens permet identificar-ne l'abast i les limitacions respecte al caràcter transformador i la seva resistència a les dinàmiques de la ciutat neoliberal. A partir d'aquesta reflexió i de la meva pròpia posició situada i crítica al món, em proposo analitzar les experiències i imaginaris comunitaris i les utopies quotidianes a diferents barris de grans ciutats, vinculant-los amb els conceptes de desig i reproducció social des de les veus i vivències dels seus protagonistes. D'aquesta manera, busco aprofundir en la idea de justícia urbana que es trasllueix als seus testimonis. L'objectiu és desafiar la lògica del sistema simbòlic-material heteropatriarcal i neoliberal, tot construint un discurs que reconegui la multiplicitat i la diferència i la possibilitat real de crear espais de convivència alliberadors que són exemples de justícia urbana. Per desenvolupar una anàlisi crítica dels conceptes que sustenten aquesta investigació, situaré aquest estudi en el marc de l'obra d'Henri Lefebvre sobre l'espaitemps urbà i el dret a la ciutat, adoptant una perspectiva feminista que posi atenció a les necessitats i els cures. Exploraré els espais-temps inesperats com un possible motor per a la creació d'utopies quotidianes, és a dir, llocs on allò utòpic s'entrellaça amb allò ordinari, donant lloc a pràctiques diàries innovadores i imprevistes. Els cossos que transiten per aquests espais utòpics són els principals agents de canvi social, gràcies a les relacions i experiències que els exposen a una reeducació constant del desig i el vincle social. Aquestes relacions, estructurades en xarxes de reproducció social compartida, configuren el nostre mapa urbà quotidià, ple d'experiències transformadores que desafien el paradigma economicosocial dominant de la ciutat neoliberal. Per a aquesta investigació, he analitzat diferents experiències comunitàries a barris amb un perfil sociodemogràfic diferent, a cadascuna d'aquestes ciutats: Barcelona, Madrid i Roma. Aquests llocs són exemples d'espais autogestionats i d'activitats socioculturals que han sorgit ai des dels marges. L'elecció d'aquests casos és deguda a la seva història de lluita, els patrons migratoris, la composició de classes i la manera com aquests factors es relacionen amb el territori i l'arquitectura de cada barri. El meu treball es divideix en dues parts principals: una revisió d'arxius municipals i un treball de camp on vaig observar els espais autogestionats que van sorgir a partir de processos de reapropiació a cadascun dels barris estudiats i als quals es refereix l'anàlisi etnogràfica.La meva conclusió és que necessitem donar visibilitat a aquestes experiències, autèntiques utopies quotidianes, que confronten amb les dinàmiques mercantilitzades de la gentrificació que són els autèntics obstacles per a la justícia urbana i la igualtat de gènere

Diffusion MRI Findings in Encephalopathy Induced by Immunosuppressive Therapy after Liver Transplantation

Neurological complications are common after liver transplantation, as they affect up to one-third of the transplanted patients and are associated with significant morbidity. The introduction of calcineurin inhibitors, cyclosporine A and tacrolimus, in immunosuppressive regimens significantly improved the outcome of solid-organ transplantation even though immunosuppression-associated neurotoxicity remains a significant complication, particularly occurring in about 25% of cases after liver transplantation. The immunosuppressant cyclosporine A and tacrolimus have been associated with the occurrence of major neurological complications, diffuse encephalopathy being the most common. The biochemical and pathogenetic basis of calcineurin inhibitors-induced neurotoxicity are still unclear although several mechanisms have been suggested. Early recognition of symptoms could help reduce neurotoxic event. The aim of the study was to evaluate cerebral changes through MRI, in particular with diffusion-weighted images (DWI) and apparent diffusion coefficient (ADC) maps, in two patients undergoing liver transplantation after immunosuppressive therapy. We describe two patients in which clinical pictures, presenting as a severe neurological condition, early after orthotopic liver transplantation during immunosuppression therapy, showed a different evolution in keeping with evidence of focal-multifocal lesions at DWI and ADC maps. At clinical onset, DWI showed hyperintensity of the temporo-parieto-occipital cortex with normal ADC values in the patient with following good clinical recovery and decreased values in the other one; in the latter case, MRI abnormalities were still present after ten days, until the patient's exitus. The changes in DWI with normal ADC may be linked to brain edema with a predominant vasogenic component and therefore reversible, while the reduction in ADC is due to cytotoxic edema and linked to more severe, nonreversible, clinical picture. Brain MRI and particularly DWI and ADC maps provide not only a good and early representation of neurological complications during immunosuppressant therapy but can also provide a useful prognostic tool on clinical outcome of the patient

Optimal Control for Articulated Soft Robots

Soft robots can execute tasks with safer interactions. However, control techniques that can effectively exploit the systems' capabilities are still missing. Differential dynamic programming (DDP) has emerged as a promising tool for achieving highly dynamic tasks. But most of the literature deals with applying DDP to articulated soft robots by using numerical differentiation, in addition to using pure feed-forward control to perform explosive tasks. Further, underactuated compliant robots are known to be difficult to control and the use of DDP-based algorithms to control them is not yet addressed. We propose an efficient DDP-based algorithm for trajectory optimization of articulated soft robots that can optimize the state trajectory, input torques, and stiffness profile. We provide an efficient method to compute the forward dynamics and the analytical derivatives of series elastic actuators (SEA)/variable stiffness actuators (VSA) and underactuated compliant robots. We present a state-feedback controller that uses locally optimal feedback policies obtained from DDP. We show through simulations and experiments that the use of feedback is crucial in improving the performance and stabilization properties of various tasks. We also show that the proposed method can be used to plan and control underactuated compliant robots, with varying degrees of underactuation effectively.Comment: 14 pages, 15 figures, IEEE Transaction on Robotics (TRO

Asymmetric posterior reversible encephalopathy syndrome in patient with hyperplastic anterior choroidal artery

We describe a case of asymmetric PRES due to the presence of hyperplastic anterior choroidal artery (AChA) in a man affected by sever hypertension. Posterior reversible encephalopathy syndrome (PRES) has become synonymous with a unique pattern of brain vasogenic edema and predominates in the parietal and occipital regions, accompanied by clinical neurological alterations. Sever hypertension is a risk factor that exceeds the limits of brain autoregulation, leading to breakthrough brain edema. In our knowledge this is the first case reported in literature, in which a similar vascular abnormality is linked to a PRES syndrome

A robust iterative learning control for continuous-time nonlinear systems with disturbances

In this paper, we study the trajectory tracking problem using iterative learning control for continuous-time nonlinear systems with a generic fixed relative degree in the presence of disturbances. This class of controllers iteratively refine the control input relying on the tracking error of the previous trials and some properly tuned learning gains. Sufficient conditions on these gains guarantee the monotonic convergence of the iterative process. However, the choice of the gains is heuristically hand-tuned given an approximated system model and no information on the disturbances. Thus, in the cases of inaccurate knowledge of the model or iteration-varying measurement errors, external disturbances, and delays, the convergence condition is unlikely to be verified at every iteration. To overcome this issue, we propose a robust convergence condition, which ensures the applicability of the pure feedforward control even if other classical conditions are not fulfilled for some trials due to the presence of disturbances. Furthermore, we quantify the upper bound of the nonrepetitive disturbance that the iterative algorithm is able to handle. Finally, we validate the convergence condition simulating the dynamics of a two degrees of freedom underactuated arm with elastic joints, where one is active, and the other is passive, and a Franka Emika Panda manipulator

Fishing for Data: Modeling, Optimal Planning, and Iterative Learning Control for Flexible Link Robots

In this work, we address the problem of precise motion planning and control of flexible-link robots for throwing small objects. Thanks to lightweight materials and elastic bodies, flexible robots can perform fast motions with few actuators. However, they need a planning and control strategy capable of exploiting the robot’s elasticity, negotiating with the system’s underactuation, and compensating for the model’s uncertainties. To solve this challenging task, we 1) compare multiple discrete models for continuum robots’ dynamics and, after selecting a lumped-parameter (LPs) model, experimentally identify its parameters; 2) plan the robot motion via a differential-dynamic-programming-based strategy tailored for flexible-link robots; and 3) employ an iterative learning control (ILC) approach to close the reality-gap. Combining these three steps allows us to execute precise throwing tasks with flexible-link robots. The strategy’s effectiveness has been validated via simulations and experiments with varying trajectories and payloads. We applied the aforementioned approach to realize a throwing motion with a fishing rod for environmental monitoring

The role of time-resolved imaging of contrast kinetics (TRICKS) magnetic resonance angiography (MRA) in the evaluation of head-neck vascular anomalies: A preliminary experience

Objectives: In this preliminary report, we describe our experience with time-resolved imaging of contrast kinetics-MR angiography (TRICKS-MRA) in the assessment of head-neck vascular anomalies (HNVAs). Methods: We prospectively studied six consecutive patients with clinically suspected or diagnosed HNVAs. All of them underwent TRICKS-MRA of the head and neck as part of the routine for treatment planning. A digital subtraction angiography (DSA) was also performed. Results: TRICKS-MRA could be achieved in all cases. Three subjects were treated based on TRICKS-MRA imaging findings and subsequent DSA examination. In all of them, DSA confirmed the vascular architecture of HNVAs shown by TRICKS-MRA. In the other three patients, a close follow up to assess the evolution of the suspected haemangioma was preferred. Conclusions: TRICKS sequences add important diagnostic information in cases of HNVAs, helpful for therapeutic decisions and post-treatment follow up. We recommend TRICKSMRA use (if technically possible) as part of routine MRI protocol for HNVAs, representing a possible alternative imaging tool to conventional DSA