A fast Monte-Carlo method with a Reduced Basis of Control Variates applied to Uncertainty Propagation and Bayesian Estimation

The Reduced-Basis Control-Variate Monte-Carlo method was introduced recently in [S. Boyaval and T. Leli\`evre, CMS, 8 2010] as an improved Monte-Carlo method, for the fast estimation of many parametrized expected values at many parameter values. We provide here a more complete analysis of the method including precise error estimates and convergence results. We also numerically demonstrate that it can be useful to some parametrized frameworks in Uncertainty Quantification, in particular (i) the case where the parametrized expectation is a scalar output of the solution to a Partial Differential Equation (PDE) with stochastic coefficients (an Uncertainty Propagation problem), and (ii) the case where the parametrized expectation is the Bayesian estimator of a scalar output in a similar PDE context. Moreover, in each case, a PDE has to be solved many times for many values of its coefficients. This is costly and we also use a reduced basis of PDE solutions like in [S. Boyaval, C. Le Bris, Nguyen C., Y. Maday and T. Patera, CMAME, 198 2009]. This is the first combination of various Reduced-Basis ideas to our knowledge, here with a view to reducing as much as possible the computational cost of a simple approach to Uncertainty Quantification

Mechanical Thrombectomy for Tandem Occlusions of the Internal Carotid Artery—Results of a Conservative Approach for the Extracranial Lesion

Background: Mechanical thrombectomy (MT) is of clinical benefit for patients with extracranial-intracranial tandem lesions of anterior circulation. However, the optimal approach to the cervical lesion of the internal carotid artery (ICA) during MT has yet to be established. Data on a conservative approach for the proximal lesion during the acute phase are scarce.Methods: A retrospective study on an institutional, prospective database was conducted. We included patients with anterior circulation stroke presenting with a tandem lesion that was approached conservatively during MT.Results: Thirty-five 35 patients were included, of whom 25 (71.4%) had an atheromatous ICA lesion and 10 (28.6%) a dissection. Despite implementing a conservative strategy, acute percutaneous transluminal angioplasty (PTA) and/or stenting was necessary in 8 (22.9%) and 3 patients (8.6%), respectively. Of 27 surviving patients, 7 (25.9%) underwent delayed treatment of the ICA lesion. No new embolic events occurred between MT and delayed treatment. A favorable clinical outcome (mRS ≤ 2) was achieved in 15/35 patients (45.7%) and was associated with higher baseline ASPECTS (OR 1.62, 95% CI 1.08–2.45, p = 0.002) and successful recanalization (OR 9.39, 95% CI 1.92–45.80, p = 0.0005). Successful recanalization (TICI ≥ 2B) itself was observed in 54.3% of patients and was more likely with acute treatment of the proximal ICA lesion (OR 6.3, 95% CI 11–35.67, p = 0.03) and, more importantly, by the use of distal access catheters (OR 16.25, 95% CI 3.06–86.41, p = 0.0001).Conclusion: A conservative approach for ICA lesions during MT is feasible and offers favorable outcomes and successful recanalization for a significant proportion of patients. However, acute treatment of the cervical lesion is often necessary (31.4%) to make the distal occlusion accessible. Clinical outcome is influenced by the size of the baseline ischemic core and by successful recanalization; the latter is strongly favored by the use of distal access catheters to pass the proximal lesion. The fact that acute treatment of the ICA lesion favored intracranial recanalization but had no effect on clinical outcome is probably due to sample size, emphasizing the need for large scale, randomized studies to determine the optimal treatment strategy for this pathology

Diagnostic and therapeutic implications of intracranial thrombus characteristics in the acute phase of ischemic stroke

Une recanalisation suffisante n’est obtenue par la thrombectomie que dans 70-80% des cas et bien souvent après plusieurs tentatives. Mieux adapter le traitement au thrombus pourrait permettre d’améliorer ce résultat. Les connaissances actuelles sur le thrombus intracrânien présentent des applications limitées tant sur le versant diagnostic que thérapeutique. C’est pour cela que nous avons souhaité étudier : 1) la variabilité au cours du temps de l’aspect du thrombus intracrânien en IRM à la phase aigüe de l’infarctus cérébral ; 2) la réponse à différentes techniques de thrombectomie en fonction du type de thrombi.La probabilité d’observer un Susceptibility Vessel Sign (SVS) sur la séquence T2* augmente en fonction du temps entre le début des symptômes et la réalisation de l’IRM; mettant en évidence l’existence de phénomènes dynamiques modifiant la composition du thrombus lors de sa période d’incubation au site d’occlusion. Les thrombus SVS-, correspondant à des thrombus riches en fibrine, élastiques et difficiles à extraire semblent plus fréquents lors de la fenêtre thérapeutique précoce. Ces variations seront confirmées par une corrélation radio-histologique. D’autre part, un retrait rapide du stent lors de la thrombectomie permet d’augmenter les chances de recanalisation complète au premier passage en lors d’expériences in vitro sur thrombus riche en fibrine (RR=4.00; 1.11-14.35; Pint=0.048) comme in vivo sur thrombus SVS- (RR 95%IC = 4.30 [1.80-10.24]). Cette technique s’avère également efficace quel que soit le type de thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) et in vivo dans une large série de 320 patients (OR, 2.88 [1.81-4.59]). Une étude randomisée est nécessaire pour confirmer ces résultats.Sufficient recanalization is achieved by thrombectomy only in 70-80% of cases and often after several attempts. Better adaptation of the treatment to the thrombus could improve this result. Current knowledge of intracranial thrombus is limited in both diagnostic and therapeutic applications. For this reason, we wished to study: 1) the variability over time of the appearance of intracranial thrombus on MRI in the acute phase of cerebral infarction; 2) the response to different thrombectomy techniques depending on the type of thrombi.The probability of observing a Susceptibility Vessel Sign (SVS) on the T2* sequence increases with the time between the onset of symptoms and MRI images acquisition, highlighting the existence of dynamic phenomena modifying the composition of the thrombus during its incubation period at the occlusion site. SVS- thrombi, corresponding to fibrin-rich thrombi, which are elastic and difficult to extract, seem to be more frequent during the early therapeutic window. These variations will be confirmed by a radio-histological correlation. On the other hand, rapid removal of the stent during thrombectomy increases the chances of complete recanalization after a single pass in both in vitro experiments with fibrin-rich thrombus (RR=4.00; 1.11-14.35; Pint=0.048) and in vivo with SVS- thrombus (RR 95%IC = 4.30 [1.80-10.24]). This technique was also effective regardless of the type of thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) and in vivo in a large series of 320 patients (OR, 2.88 [1.81-4.59]). A randomized trial is needed to confirm these results

Implications diagnostiques et thérapeutiques des caractéristiques du thrombus intracrânien à la phase aigüe de l'infarctus cérébral

Sufficient recanalization is achieved by thrombectomy only in 70-80% of cases and often after several attempts. Better adaptation of the treatment to the thrombus could improve this result. Current knowledge of intracranial thrombus is limited in both diagnostic and therapeutic applications. For this reason, we wished to study: 1) the variability over time of the appearance of intracranial thrombus on MRI in the acute phase of cerebral infarction; 2) the response to different thrombectomy techniques depending on the type of thrombi.The probability of observing a Susceptibility Vessel Sign (SVS) on the T2* sequence increases with the time between the onset of symptoms and MRI images acquisition, highlighting the existence of dynamic phenomena modifying the composition of the thrombus during its incubation period at the occlusion site. SVS- thrombi, corresponding to fibrin-rich thrombi, which are elastic and difficult to extract, seem to be more frequent during the early therapeutic window. These variations will be confirmed by a radio-histological correlation. On the other hand, rapid removal of the stent during thrombectomy increases the chances of complete recanalization after a single pass in both in vitro experiments with fibrin-rich thrombus (RR=4.00; 1.11-14.35; Pint=0.048) and in vivo with SVS- thrombus (RR 95%IC = 4.30 [1.80-10.24]). This technique was also effective regardless of the type of thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) and in vivo in a large series of 320 patients (OR, 2.88 [1.81-4.59]). A randomized trial is needed to confirm these results.Une recanalisation suffisante n’est obtenue par la thrombectomie que dans 70-80% des cas et bien souvent après plusieurs tentatives. Mieux adapter le traitement au thrombus pourrait permettre d’améliorer ce résultat. Les connaissances actuelles sur le thrombus intracrânien présentent des applications limitées tant sur le versant diagnostic que thérapeutique. C’est pour cela que nous avons souhaité étudier : 1) la variabilité au cours du temps de l’aspect du thrombus intracrânien en IRM à la phase aigüe de l’infarctus cérébral ; 2) la réponse à différentes techniques de thrombectomie en fonction du type de thrombi.La probabilité d’observer un Susceptibility Vessel Sign (SVS) sur la séquence T2* augmente en fonction du temps entre le début des symptômes et la réalisation de l’IRM; mettant en évidence l’existence de phénomènes dynamiques modifiant la composition du thrombus lors de sa période d’incubation au site d’occlusion. Les thrombus SVS-, correspondant à des thrombus riches en fibrine, élastiques et difficiles à extraire semblent plus fréquents lors de la fenêtre thérapeutique précoce. Ces variations seront confirmées par une corrélation radio-histologique. D’autre part, un retrait rapide du stent lors de la thrombectomie permet d’augmenter les chances de recanalisation complète au premier passage en lors d’expériences in vitro sur thrombus riche en fibrine (RR=4.00; 1.11-14.35; Pint=0.048) comme in vivo sur thrombus SVS- (RR 95%IC = 4.30 [1.80-10.24]). Cette technique s’avère également efficace quel que soit le type de thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) et in vivo dans une large série de 320 patients (OR, 2.88 [1.81-4.59]). Une étude randomisée est nécessaire pour confirmer ces résultats

Implications diagnostiques et thérapeutiques des caractéristiques du thrombus intracrânien à la phase aigüe de l'infarctus cérébral

Sufficient recanalization is achieved by thrombectomy only in 70-80% of cases and often after several attempts. Better adaptation of the treatment to the thrombus could improve this result. Current knowledge of intracranial thrombus is limited in both diagnostic and therapeutic applications. For this reason, we wished to study: 1) the variability over time of the appearance of intracranial thrombus on MRI in the acute phase of cerebral infarction; 2) the response to different thrombectomy techniques depending on the type of thrombi.The probability of observing a Susceptibility Vessel Sign (SVS) on the T2* sequence increases with the time between the onset of symptoms and MRI images acquisition, highlighting the existence of dynamic phenomena modifying the composition of the thrombus during its incubation period at the occlusion site. SVS- thrombi, corresponding to fibrin-rich thrombi, which are elastic and difficult to extract, seem to be more frequent during the early therapeutic window. These variations will be confirmed by a radio-histological correlation. On the other hand, rapid removal of the stent during thrombectomy increases the chances of complete recanalization after a single pass in both in vitro experiments with fibrin-rich thrombus (RR=4.00; 1.11-14.35; Pint=0.048) and in vivo with SVS- thrombus (RR 95%IC = 4.30 [1.80-10.24]). This technique was also effective regardless of the type of thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) and in vivo in a large series of 320 patients (OR, 2.88 [1.81-4.59]). A randomized trial is needed to confirm these results.Une recanalisation suffisante n’est obtenue par la thrombectomie que dans 70-80% des cas et bien souvent après plusieurs tentatives. Mieux adapter le traitement au thrombus pourrait permettre d’améliorer ce résultat. Les connaissances actuelles sur le thrombus intracrânien présentent des applications limitées tant sur le versant diagnostic que thérapeutique. C’est pour cela que nous avons souhaité étudier : 1) la variabilité au cours du temps de l’aspect du thrombus intracrânien en IRM à la phase aigüe de l’infarctus cérébral ; 2) la réponse à différentes techniques de thrombectomie en fonction du type de thrombi.La probabilité d’observer un Susceptibility Vessel Sign (SVS) sur la séquence T2* augmente en fonction du temps entre le début des symptômes et la réalisation de l’IRM; mettant en évidence l’existence de phénomènes dynamiques modifiant la composition du thrombus lors de sa période d’incubation au site d’occlusion. Les thrombus SVS-, correspondant à des thrombus riches en fibrine, élastiques et difficiles à extraire semblent plus fréquents lors de la fenêtre thérapeutique précoce. Ces variations seront confirmées par une corrélation radio-histologique. D’autre part, un retrait rapide du stent lors de la thrombectomie permet d’augmenter les chances de recanalisation complète au premier passage en lors d’expériences in vitro sur thrombus riche en fibrine (RR=4.00; 1.11-14.35; Pint=0.048) comme in vivo sur thrombus SVS- (RR 95%IC = 4.30 [1.80-10.24]). Cette technique s’avère également efficace quel que soit le type de thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) et in vivo dans une large série de 320 patients (OR, 2.88 [1.81-4.59]). Une étude randomisée est nécessaire pour confirmer ces résultats

Implications diagnostiques et thérapeutiques des caractéristiques du thrombus intracrânien à la phase aigüe de l'infarctus cérébral

Sufficient recanalization is achieved by thrombectomy only in 70-80% of cases and often after several attempts. Better adaptation of the treatment to the thrombus could improve this result. Current knowledge of intracranial thrombus is limited in both diagnostic and therapeutic applications. For this reason, we wished to study: 1) the variability over time of the appearance of intracranial thrombus on MRI in the acute phase of cerebral infarction; 2) the response to different thrombectomy techniques depending on the type of thrombi.The probability of observing a Susceptibility Vessel Sign (SVS) on the T2* sequence increases with the time between the onset of symptoms and MRI images acquisition, highlighting the existence of dynamic phenomena modifying the composition of the thrombus during its incubation period at the occlusion site. SVS- thrombi, corresponding to fibrin-rich thrombi, which are elastic and difficult to extract, seem to be more frequent during the early therapeutic window. These variations will be confirmed by a radio-histological correlation. On the other hand, rapid removal of the stent during thrombectomy increases the chances of complete recanalization after a single pass in both in vitro experiments with fibrin-rich thrombus (RR=4.00; 1.11-14.35; Pint=0.048) and in vivo with SVS- thrombus (RR 95%IC = 4.30 [1.80-10.24]). This technique was also effective regardless of the type of thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) and in vivo in a large series of 320 patients (OR, 2.88 [1.81-4.59]). A randomized trial is needed to confirm these results.Une recanalisation suffisante n’est obtenue par la thrombectomie que dans 70-80% des cas et bien souvent après plusieurs tentatives. Mieux adapter le traitement au thrombus pourrait permettre d’améliorer ce résultat. Les connaissances actuelles sur le thrombus intracrânien présentent des applications limitées tant sur le versant diagnostic que thérapeutique. C’est pour cela que nous avons souhaité étudier : 1) la variabilité au cours du temps de l’aspect du thrombus intracrânien en IRM à la phase aigüe de l’infarctus cérébral ; 2) la réponse à différentes techniques de thrombectomie en fonction du type de thrombi.La probabilité d’observer un Susceptibility Vessel Sign (SVS) sur la séquence T2* augmente en fonction du temps entre le début des symptômes et la réalisation de l’IRM; mettant en évidence l’existence de phénomènes dynamiques modifiant la composition du thrombus lors de sa période d’incubation au site d’occlusion. Les thrombus SVS-, correspondant à des thrombus riches en fibrine, élastiques et difficiles à extraire semblent plus fréquents lors de la fenêtre thérapeutique précoce. Ces variations seront confirmées par une corrélation radio-histologique. D’autre part, un retrait rapide du stent lors de la thrombectomie permet d’augmenter les chances de recanalisation complète au premier passage en lors d’expériences in vitro sur thrombus riche en fibrine (RR=4.00; 1.11-14.35; Pint=0.048) comme in vivo sur thrombus SVS- (RR 95%IC = 4.30 [1.80-10.24]). Cette technique s’avère également efficace quel que soit le type de thrombus, in vitro (RR=1.83; 95%CI, 1.12-2.99) et in vivo dans une large série de 320 patients (OR, 2.88 [1.81-4.59]). Une étude randomisée est nécessaire pour confirmer ces résultats

Follow-up of intracranial aneurysms treated with stent-assisted coiling: Comparison of contrast-enhanced MRA, time-of-flight MRA, and digital subtraction angiography

International audienceBackground and purposeData about non-invasive follow-up of aneurysm after stent-assisted coiling is scarce. We aimed to compare time-of-flight (TOF) magnetic resonance angiography (MRA) (3D-TOF-MRA) and contrast-enhanced MRA (CE-MRA) at 3-Tesla, with digital subtraction angiography (DSA) for evaluating aneurysm occlusion and parent artery patency after stent-assisted coiling.Materials and methodsIn this retrospective single-center study, patients were included if they had an intracranial aneurysm treated by stent-assisted coiling between March 2008 and June 2015, followed with both MRA sequences (3D-TOF-MRA and CE-MRA) at 3-Tesla and DSA, performed in an interval < 48 hours.ResultsThirty-five aneurysms were included. Regarding aneurysm occlusion evaluation, agreement with DSA was better for CE-MRA (K = 0.53) than 3D-TOF-MRA (K = 0.28). Diagnostic accuracies for aneurysm remnant depiction were similar for 3D-TOF-MRA and CE-MRA (P = 1). Both 3D-TOF-MRA (K = 0.05) and CE-MRA (K = −0.04) were unable to detect pathological vessel compared to DSA, without difference in accuracy (P = 0.68). For parent artery occlusion detection, agreement with DSA was substantial for 3D-TOF-MRA (K = 0.64) and moderate for CE-MRA (K = 0.45), with similar good diagnostic accuracies (P = 1).ConclusionAfter stent-assisted coiling treatment, 3D-TOF-MRA and CE-MRA demonstrated good accuracy to detect aneurysm remnant (but tended to overestimation). Although CE-MRA agreement with DSA was better, there was no statistical difference between 3D-TOF-MRA and CE-MRA accuracies. Both MRAs were unable to provide a precise evaluation of in-stent status but could detect parent vessel occlusion

Follow-up of intracranial aneurysms treated by flow diverter: comparison of three-dimensional time-of-flight MR angiography (3D-TOF-MRA) and contrast-enhanced MR angiography (CE-MRA) sequences with digital subtraction angiography as the gold standard

International audienceBackground and purpose: Follow-up of intracranial aneurysms treated by flow diverter with MRI is complicated by imaging artifacts produced by these devices. This study compares the diagnostic accuracy of three-dimensional time-of-flight MR angiography (3D-TOF-MRA) and contrast-enhanced MRA (CE-MRA) at 3 T for the evaluation of aneurysm occlusion and parent artery patency after flow diversion treatment, with digital subtraction angiography (DSA) as the gold standard.Materials and methods: Patients treated with flow diverters between January 2009 and January 2013 followed by MRA at 3 T (3D-TOF-MRA and CE-MRA) and DSA within a 48 h period were included in a prospective single-center study. Aneurysm occlusion was assessed with full and simplified Montreal scales and parent artery patency with three-grade and two-grade scales.Results: Twenty-two patients harboring 23 treated aneurysms were included. Interobserver agreement using simplified scales for occlusion (Montreal) and parent artery patency were higher for DSA (0.88 and 0.61) and CE-MRA (0.74 and 0.55) than for 3D-TOF-MRA (0.51 and 0.02). Intermodality agreement was higher for CE-MRA (0.88 and 0.32) than for 3D-TOF-MRA (0.59 and 0.11). CE-MRA yielded better accuracy than 3D-TOF-MRA for aneurysm remnant detection (sensitivity 83% vs 50%; specificity 100% vs 100%) and for the status of the parent artery (specificity 63% vs 32%; sensitivity 100% vs 100%).Conclusions: At 3 T, CE-MRA is superior to 3D-TOF-MRA for the evaluation of aneurysm occlusion and parent artery patency after flow diversion treatment. However, intraluminal evaluation remains difficult with MRA regardless of the sequence used

Parenchymal FLAIR hyperintensity before thrombolysis is a prognostic factor of ischemic stroke outcome at 3 Tesla

International audienceBACKGROUND: The goal of the present study was to determine whether the presence or absence of parenchymal FLAIR hyperintensity alone, before thrombolysis, might be a predictive factor of ischemic stroke outcomes after the acute phase of stroke and at 3 months. MATERIALS AND METHODS: We retrospectively included 84 patients with an ischemic stroke between November 2007 and March 2012, who underwent 3T MRI, were treated by thrombolysis, and had medical follow-up at 3 months. Two readers analyzed parenchymal FLAIR visibility. Logistic regressions were performed for NIHSS difference (NIHSS at admission - NIHSS at the end of hospitalization) and for 3 months modified Ranking Score (mRS). Predictive values of positive parenchymal FLAIR for identifying poor outcome at discharge and at 3 months were estimated. RESULTS: Parenchymal FLAIR positivity was not predictive of NIHSS difference but it predicted poor outcome at 3 months (sensitivity: 0.49 [0.37-0.60], specificity: 0.69 [0.46-0.91], positive predictive value: 0.87 [0.76-0.98] and negative predictive value: 0.24 [0.12-0.36]). CONCLUSIONS: At 3 Tesla, the presence of a parenchymal hyperintense FLAIR signal before thrombolysis is predictive of a poor clinical outcome at 3 months

Patient and aneurysm factors associated with aneurysm rupture in the population of the ARETA study

International audienceIdentifying patients with intracranial aneurysms (IA) who have a high risk of rupture is critical to determine optimal management. ARETA (Analysis of Recanalization after Endovascular Treatment of intracranial Aneurysm) is a prospective, multicenter study, dedicated to evaluating endovascular treatment of IA. We aimed to identify factors associated with ruptured status, using this very large series of patients with ruptured and unruptured aneurysms