Background and Purpose: This study aims to demonstrate that the so-called Islamic legacy calendar... more Background and Purpose: This study aims to demonstrate that the so-called Islamic legacy calendars are of the Gregorian-like type far from corresponding to the properties of the synodic lunar month. This unexpected result provided the first stone from which the search for a coherent definition of legacy criterion has been undertaken in this work. Material and Methods: To this end, distributions of time lag (∆t 0), the time distance between the lunar conjunction (LC) and the first lunar day of the month, were processed and used to estimate the 1 st −Day rejection index (R I) for four computerized calendar paradigms used in Lausanne city, between1938 and 2038. Those estimates measured the deviations from the lunar synodic properties caused by the underlying hypotheses. In addition, new synoptic figures of the projected 2023/1444H Ramadan calendars in twelve pilot cities were computed to highlight the fundamental reason for mismatch along with specific assessment. Those figures also aimed to illustrate the competitive effects of four environmental parameters on final issues, namely: LC, latitude, time zone and season. Results: Several results were found: R I was ranging between 45% and 90% while the corresponding rejection thresholds were between 8h and 18h. The synoptic figures, while fully explaining the similarities and differences between the calendars in and between cities with all their respective 1 st −Day dates being summarized in "Confusion Tables", they also contributed to demonstrate that all the residual flaws of the Islamic calendars were caused by explicit and implicit assumptions of unfounded "day reference times" (DRT), as if the lunar context was assimilated to a Gregorian-like one. Conclusion: The results were finally analyzed within the framework of the "inclusive science approach" (ISA) and a new proposal was made in favor of a "single and universal" Islamic calendar legacy definition, which conforms on the one hand, to the properties of the lunar synodic month and on the other hand, to lunar Islamic requirements.
Journal of NeuroInterventional Surgery, Feb 15, 2016
Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular a... more Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning. Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) aneurysm occlusion. We included 12 consecutive patients with sidewall aneurysms located in the internal carotid or vertebral artery. The measured porosity of the 12 deployed virtual FDSs was 83±3% (mean±SD). Nine aneurysms were occluded during the 12 months' follow-up, whereas three were not. A significant (p=0.05) area under the curve (AUC) was found for spatiotemporal mean velocity reduction in the aneurysms: AUC=0.889±0.113 (mean±SD) corresponding to a minimum velocity reduction threshold of 0.353 for occlusion to occur. The 95% CI of the AUC was 0.66 to 1.00. The sensitivity and specificity of the method were ∼99% and ∼67%, respectively. For both wall shear stress and pressure reductions in aneurysms no thresholds could be determined: AUC=0.63±0.16 (p=0.518) and 0.67±0.165 (p=0.405), respectively. For successful FDS treatment the post-stent average velocity in sidewall intracranial aneurysms must be reduced by at least one-third from the initial pre-stent conditions.
Inlet boundary conditions (BCs) are important inputs of computational fluid dynamics (CFD) in int... more Inlet boundary conditions (BCs) are important inputs of computational fluid dynamics (CFD) in intracranial aneurysms (IAs). We performed sensibility analysis of CFD to different inlet BCs applied to illustrative patient-specific aneurysm-vessel geometry. BCs corresponding to generic and patient-specific pulsatile flow curves were applied to three vascular geometry models of carotid ophthalmic aneurysm-vessel geometry, in which the inlet lengths were different. CFD outcomes were compared to high frame rate Digital Subtraction Angiography (DSA) sequences. The streamlines were found to match contrast agent (CA) motion pattern in the case where the non-truncated inlet vessel model was coupled to generic Womersley BC solution. Even though dynamic pressure loss (55%) was equal for all models and different BCs, the minimum distance to wall of the fastest velocity fields for the non-truncated model was significantly larger (p=0.002) and mean vorticity sign was different. Significant difference in spatial distributions of wall shear stress (WSS) and oscillating shear stress index (OSI) was found in aneurysm between Womersley and Plugflow BC conditions, only. Reliable CFD for carotid ophthalmic aneurysm would require avoiding truncation of the inlet vessel to be independent of the solution applied to generate CFD.
Journal of neurointerventional surgery, Jan 3, 2014
Flow diverter stents (FDS) have been effectively used for the endovascular treatment of sidewall ... more Flow diverter stents (FDS) have been effectively used for the endovascular treatment of sidewall intracranial aneurysms (IAs). Unlike standard endovascular treatments used to exclude directly the aneurysm bulge from the parent vessel, FDS induce reduction in the intra-aneurysmal flow and promote progressive and stable thrombosis therein. The advent of FDS has therefore increased the need for understanding of IA hemodynamics. We proposed the use of the most recently evolved four-dimensional (4D) flow MRI technique to evaluate qualitatively and quantitatively post-FDS flow modification in 10 patients. We report intra-aneurysmal velocity measurements and the influence of metal artifacts induced by the stent. An index was defined to quantitatively measure flow changes-namely, the proportional velocity reduction ratio (PVRR)-with ranges from 34.6% to 71.1%. Furthermore, we could compare streamlines characterizing the post-stent flow patterns in five patients in whom the intra-aneurysmal ...
We investigated the flow modifications induced by a large panel of commercial-off-the-shelf (COTS... more We investigated the flow modifications induced by a large panel of commercial-off-the-shelf (COTS) intracranial stents in an idealized sidewall intracranial aneurysm (IA). Flow velocities in IA silicone model were assessed with and without stent implantation using particle imaging velocimetry (PIV). The use of the recently developed multi-time-lag method has allowed for uniform and precise measurements of both high and low velocities at IA neck and dome, respectively. Flow modification analysis of both regular (RSs) and flow diverter stents (FDSs) was subsequently correlated with relevant geometrical stent parameters. Flow reduction was found to be highly sensitive to stent porosity variations for regular stents RSs and moderately sensitive for FDSs. Consequently, two distinct IA flow change trends, with velocity reductions up to 50 % and 90%, were identified for high-porosity RS and low-porosity FDS, respectively. The intermediate porosity (88%) regular braided stent provided the l...
Le modele de risques SPiCE-R definit une correlation binaire entre une liste de risques generique... more Le modele de risques SPiCE-R definit une correlation binaire entre une liste de risques generiques et les processus de la norme ISO/IES TR 15504, La vraisemblance d'un risque donne depend des ecarts entre le niveau de capacite requis et le niveau de capacite effectivement atteint pour les processus qui lui sont correles. Des facteurs de risque de processus sont utilises pour moduler l'influence des ecarts sur differents attributs de processus, fies concepts de la methode d'evaluation de risques SPRIME, le projet SPEC et la taxinomie des risques definie par le Software Engineering Institute ont ete utilises pour definir la matrice reliant risques et processus. La methode de calcul de la vraisemblance des risques definit le calcul des probabilites oriente processus et met en correspondance les resultats avec l'echelle de probabilite recommandee dans les normes de l'industrie spatiale. La methode suit une mise en oeuvre quantitative de l'approche ebauchee dans l...
The three reactions pp! … 0 … 0 … 0 , … 0 … 0 · and … 0 ·· in proton-antiproton annihilation in ∞... more The three reactions pp! … 0 … 0 … 0 , … 0 … 0 · and … 0 ·· in proton-antiproton annihilation in ∞ight at 900 MeV=c are used to search for isoscalar 0 ++ and 2 ++ mesons in the mass range 1000i 2000 MeV, in particular the f0(1710). The description of both … 0 … 0 … 0 and … 0 ·· data sets requires an isoscalar tensor resonance decaying into … 0 … 0 and ·· with a mass of (1867§ 46) MeV and a width of (385§ 58) MeV. The ratio of partial widths i (··)=i (…… )i s 0:27§ 0:10. The analyses of both … 0 … 0 … 0 and … 0 ·· show no signal for the f0(1710). The … 0 ·· data set shows a strong signal of the f 0 2(1525) suggesting a large OZI rule violation for tensor meson production in pp annihilation. The … 0 … 0 … 0 data set also requires the f2(1565). The signal for the f2(1810) reported by earlier experiments is conflrmed neither in … 0 … 0 … 0 nor in … 0 ··. The analysis of … 0 … 0 · leads to an isovector tensor state decaying into … 0 · with a mass of (1698§ 44) MeV and a width of (265§ 55)...
Journal of neurointerventional surgery, Jan 15, 2016
Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular a... more Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning. Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) a...
The morphological and hemodynamic evaluations of neurovascular diseases treated with stents would... more The morphological and hemodynamic evaluations of neurovascular diseases treated with stents would benefit from noninvasive imaging techniques such as 3D time-of-flight MRI (3D-TOF) and 3D phase contrast MRI (3D-PCMRI). For this purpose, a comprehensive evaluation of the stent artifacts and their impact on the flow measurement is critical. The artifacts of a representative sample of neurovascular stents were evaluated in vitro with 3D-TOF and 3D-PCMRI sequences. The dependency of the artifacts with respect to the orientation was analyzed for each stent design as well as the impact on the flow measurement accuracy. Furthermore, the 3D-PCMRI data of four patients carrying intracranial aneurysms treated with flow diverter stents were analyzed as illustrative examples. The stent artifacts were mainly confined to the stent lumen therefore indicating the leading role of shielding effect. The influence of the stent design and its orientation with respect to the transmitting MR coils were hi...
Hemodynamics play a driving role in the life cycle of brain aneurysms from initiation through gro... more Hemodynamics play a driving role in the life cycle of brain aneurysms from initiation through growth until eventual rupture. The specific factors behind aneurysm growth, especially in small aneurysms, are not well elucidated. The goal of this study was to differentiate focal versus general growth and to analyze the hemodynamic microenvironment at the sites of enlargement in small cerebral aneurysms. Small aneurysms showing growth during follow-up were identified from our prospective aneurysm database. Three dimensional rotational angiography (3DRA) studies before and after morphology changes were available for all aneurysms included in the study, allowing for detailed shape and computational fluid dynamic (CFD) based hemodynamic analysis. Six patients fulfilled the inclusion criteria. Two different types of change were observed: focal growth, with bleb or blister formation in three, and global aneurysm enlargement accompanied by neck broadening in other three patients. Areas of foca...
Stroke has become an absolute emergency that is treated by additional endovascular means or by re... more Stroke has become an absolute emergency that is treated by additional endovascular means or by replacing pharmacological options. Modern neuroradiological techniques such as computed tomography (CT) allow us to examine multiple parameters of the diseased brain. These focused on the parenchyma and hemodynamics for pretherapeutic decisions. However, it has become evident that the clot is the current target for interventional measures. Clot length is established as a marker for recanalization. The dense artery sign is known as an acute CT sign of stroke that is readily visible on acute nonenhanced CT. The rationale behind our study was to study if clot density might represent clot vulnerability or resistance to treatment. We conducted a prospective study of all consecutive stroke patients admitted to our hospital over 1 year, who presented with signs of acute middle cerebral artery stroke within the therapeutic window, and who underwent either intravenous or combined intravenous and in...
Recent advances in 3D-PCMRI (phase contrast MRI) sequences allow for measuring the complex hemody... more Recent advances in 3D-PCMRI (phase contrast MRI) sequences allow for measuring the complex hemodynamics in cerebral arteries. However, the small size of these vessels vs spatial resolution can lead to non-negligible partial volume artifacts, which must be taken into account when computing blood flow rates. For this purpose, we combined the velocity information provided by 3D-PCMRI with vessel geometry measured with 3DTOF (time of flight MRI) or 3DRA (3D rotational angiography) to correct the partial volume effects in flow rate assessments. The proposed methodology was first tested in vitro on cylindrical and patient specific vessels subject to fully controlled pulsatile flows. Both 2D- and 3D-PCMRI measurements using various spatial resolutions ranging from 20 to 1.3 voxels per vessel diameter were analyzed and compared with flowmeter baseline. Second, 3DTOF, 2D- and 3D-PCMRI measurements were performed in vivo on 35 patients harboring internal carotid artery (ICA) aneurysms indicat...
Journal of neurointerventional surgery, Jan 15, 2016
Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular a... more Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning. Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) a...
Background and Purpose: This study aims to demonstrate that the so-called Islamic legacy calendar... more Background and Purpose: This study aims to demonstrate that the so-called Islamic legacy calendars are of the Gregorian-like type far from corresponding to the properties of the synodic lunar month. This unexpected result provided the first stone from which the search for a coherent definition of legacy criterion has been undertaken in this work. Material and Methods: To this end, distributions of time lag (∆t 0), the time distance between the lunar conjunction (LC) and the first lunar day of the month, were processed and used to estimate the 1 st −Day rejection index (R I) for four computerized calendar paradigms used in Lausanne city, between1938 and 2038. Those estimates measured the deviations from the lunar synodic properties caused by the underlying hypotheses. In addition, new synoptic figures of the projected 2023/1444H Ramadan calendars in twelve pilot cities were computed to highlight the fundamental reason for mismatch along with specific assessment. Those figures also aimed to illustrate the competitive effects of four environmental parameters on final issues, namely: LC, latitude, time zone and season. Results: Several results were found: R I was ranging between 45% and 90% while the corresponding rejection thresholds were between 8h and 18h. The synoptic figures, while fully explaining the similarities and differences between the calendars in and between cities with all their respective 1 st −Day dates being summarized in "Confusion Tables", they also contributed to demonstrate that all the residual flaws of the Islamic calendars were caused by explicit and implicit assumptions of unfounded "day reference times" (DRT), as if the lunar context was assimilated to a Gregorian-like one. Conclusion: The results were finally analyzed within the framework of the "inclusive science approach" (ISA) and a new proposal was made in favor of a "single and universal" Islamic calendar legacy definition, which conforms on the one hand, to the properties of the lunar synodic month and on the other hand, to lunar Islamic requirements.
Journal of NeuroInterventional Surgery, Feb 15, 2016
Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular a... more Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning. Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) aneurysm occlusion. We included 12 consecutive patients with sidewall aneurysms located in the internal carotid or vertebral artery. The measured porosity of the 12 deployed virtual FDSs was 83±3% (mean±SD). Nine aneurysms were occluded during the 12 months' follow-up, whereas three were not. A significant (p=0.05) area under the curve (AUC) was found for spatiotemporal mean velocity reduction in the aneurysms: AUC=0.889±0.113 (mean±SD) corresponding to a minimum velocity reduction threshold of 0.353 for occlusion to occur. The 95% CI of the AUC was 0.66 to 1.00. The sensitivity and specificity of the method were ∼99% and ∼67%, respectively. For both wall shear stress and pressure reductions in aneurysms no thresholds could be determined: AUC=0.63±0.16 (p=0.518) and 0.67±0.165 (p=0.405), respectively. For successful FDS treatment the post-stent average velocity in sidewall intracranial aneurysms must be reduced by at least one-third from the initial pre-stent conditions.
Inlet boundary conditions (BCs) are important inputs of computational fluid dynamics (CFD) in int... more Inlet boundary conditions (BCs) are important inputs of computational fluid dynamics (CFD) in intracranial aneurysms (IAs). We performed sensibility analysis of CFD to different inlet BCs applied to illustrative patient-specific aneurysm-vessel geometry. BCs corresponding to generic and patient-specific pulsatile flow curves were applied to three vascular geometry models of carotid ophthalmic aneurysm-vessel geometry, in which the inlet lengths were different. CFD outcomes were compared to high frame rate Digital Subtraction Angiography (DSA) sequences. The streamlines were found to match contrast agent (CA) motion pattern in the case where the non-truncated inlet vessel model was coupled to generic Womersley BC solution. Even though dynamic pressure loss (55%) was equal for all models and different BCs, the minimum distance to wall of the fastest velocity fields for the non-truncated model was significantly larger (p=0.002) and mean vorticity sign was different. Significant difference in spatial distributions of wall shear stress (WSS) and oscillating shear stress index (OSI) was found in aneurysm between Womersley and Plugflow BC conditions, only. Reliable CFD for carotid ophthalmic aneurysm would require avoiding truncation of the inlet vessel to be independent of the solution applied to generate CFD.
Journal of neurointerventional surgery, Jan 3, 2014
Flow diverter stents (FDS) have been effectively used for the endovascular treatment of sidewall ... more Flow diverter stents (FDS) have been effectively used for the endovascular treatment of sidewall intracranial aneurysms (IAs). Unlike standard endovascular treatments used to exclude directly the aneurysm bulge from the parent vessel, FDS induce reduction in the intra-aneurysmal flow and promote progressive and stable thrombosis therein. The advent of FDS has therefore increased the need for understanding of IA hemodynamics. We proposed the use of the most recently evolved four-dimensional (4D) flow MRI technique to evaluate qualitatively and quantitatively post-FDS flow modification in 10 patients. We report intra-aneurysmal velocity measurements and the influence of metal artifacts induced by the stent. An index was defined to quantitatively measure flow changes-namely, the proportional velocity reduction ratio (PVRR)-with ranges from 34.6% to 71.1%. Furthermore, we could compare streamlines characterizing the post-stent flow patterns in five patients in whom the intra-aneurysmal ...
We investigated the flow modifications induced by a large panel of commercial-off-the-shelf (COTS... more We investigated the flow modifications induced by a large panel of commercial-off-the-shelf (COTS) intracranial stents in an idealized sidewall intracranial aneurysm (IA). Flow velocities in IA silicone model were assessed with and without stent implantation using particle imaging velocimetry (PIV). The use of the recently developed multi-time-lag method has allowed for uniform and precise measurements of both high and low velocities at IA neck and dome, respectively. Flow modification analysis of both regular (RSs) and flow diverter stents (FDSs) was subsequently correlated with relevant geometrical stent parameters. Flow reduction was found to be highly sensitive to stent porosity variations for regular stents RSs and moderately sensitive for FDSs. Consequently, two distinct IA flow change trends, with velocity reductions up to 50 % and 90%, were identified for high-porosity RS and low-porosity FDS, respectively. The intermediate porosity (88%) regular braided stent provided the l...
Le modele de risques SPiCE-R definit une correlation binaire entre une liste de risques generique... more Le modele de risques SPiCE-R definit une correlation binaire entre une liste de risques generiques et les processus de la norme ISO/IES TR 15504, La vraisemblance d'un risque donne depend des ecarts entre le niveau de capacite requis et le niveau de capacite effectivement atteint pour les processus qui lui sont correles. Des facteurs de risque de processus sont utilises pour moduler l'influence des ecarts sur differents attributs de processus, fies concepts de la methode d'evaluation de risques SPRIME, le projet SPEC et la taxinomie des risques definie par le Software Engineering Institute ont ete utilises pour definir la matrice reliant risques et processus. La methode de calcul de la vraisemblance des risques definit le calcul des probabilites oriente processus et met en correspondance les resultats avec l'echelle de probabilite recommandee dans les normes de l'industrie spatiale. La methode suit une mise en oeuvre quantitative de l'approche ebauchee dans l...
The three reactions pp! … 0 … 0 … 0 , … 0 … 0 · and … 0 ·· in proton-antiproton annihilation in ∞... more The three reactions pp! … 0 … 0 … 0 , … 0 … 0 · and … 0 ·· in proton-antiproton annihilation in ∞ight at 900 MeV=c are used to search for isoscalar 0 ++ and 2 ++ mesons in the mass range 1000i 2000 MeV, in particular the f0(1710). The description of both … 0 … 0 … 0 and … 0 ·· data sets requires an isoscalar tensor resonance decaying into … 0 … 0 and ·· with a mass of (1867§ 46) MeV and a width of (385§ 58) MeV. The ratio of partial widths i (··)=i (…… )i s 0:27§ 0:10. The analyses of both … 0 … 0 … 0 and … 0 ·· show no signal for the f0(1710). The … 0 ·· data set shows a strong signal of the f 0 2(1525) suggesting a large OZI rule violation for tensor meson production in pp annihilation. The … 0 … 0 … 0 data set also requires the f2(1565). The signal for the f2(1810) reported by earlier experiments is conflrmed neither in … 0 … 0 … 0 nor in … 0 ··. The analysis of … 0 … 0 · leads to an isovector tensor state decaying into … 0 · with a mass of (1698§ 44) MeV and a width of (265§ 55)...
Journal of neurointerventional surgery, Jan 15, 2016
Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular a... more Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning. Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) a...
The morphological and hemodynamic evaluations of neurovascular diseases treated with stents would... more The morphological and hemodynamic evaluations of neurovascular diseases treated with stents would benefit from noninvasive imaging techniques such as 3D time-of-flight MRI (3D-TOF) and 3D phase contrast MRI (3D-PCMRI). For this purpose, a comprehensive evaluation of the stent artifacts and their impact on the flow measurement is critical. The artifacts of a representative sample of neurovascular stents were evaluated in vitro with 3D-TOF and 3D-PCMRI sequences. The dependency of the artifacts with respect to the orientation was analyzed for each stent design as well as the impact on the flow measurement accuracy. Furthermore, the 3D-PCMRI data of four patients carrying intracranial aneurysms treated with flow diverter stents were analyzed as illustrative examples. The stent artifacts were mainly confined to the stent lumen therefore indicating the leading role of shielding effect. The influence of the stent design and its orientation with respect to the transmitting MR coils were hi...
Hemodynamics play a driving role in the life cycle of brain aneurysms from initiation through gro... more Hemodynamics play a driving role in the life cycle of brain aneurysms from initiation through growth until eventual rupture. The specific factors behind aneurysm growth, especially in small aneurysms, are not well elucidated. The goal of this study was to differentiate focal versus general growth and to analyze the hemodynamic microenvironment at the sites of enlargement in small cerebral aneurysms. Small aneurysms showing growth during follow-up were identified from our prospective aneurysm database. Three dimensional rotational angiography (3DRA) studies before and after morphology changes were available for all aneurysms included in the study, allowing for detailed shape and computational fluid dynamic (CFD) based hemodynamic analysis. Six patients fulfilled the inclusion criteria. Two different types of change were observed: focal growth, with bleb or blister formation in three, and global aneurysm enlargement accompanied by neck broadening in other three patients. Areas of foca...
Stroke has become an absolute emergency that is treated by additional endovascular means or by re... more Stroke has become an absolute emergency that is treated by additional endovascular means or by replacing pharmacological options. Modern neuroradiological techniques such as computed tomography (CT) allow us to examine multiple parameters of the diseased brain. These focused on the parenchyma and hemodynamics for pretherapeutic decisions. However, it has become evident that the clot is the current target for interventional measures. Clot length is established as a marker for recanalization. The dense artery sign is known as an acute CT sign of stroke that is readily visible on acute nonenhanced CT. The rationale behind our study was to study if clot density might represent clot vulnerability or resistance to treatment. We conducted a prospective study of all consecutive stroke patients admitted to our hospital over 1 year, who presented with signs of acute middle cerebral artery stroke within the therapeutic window, and who underwent either intravenous or combined intravenous and in...
Recent advances in 3D-PCMRI (phase contrast MRI) sequences allow for measuring the complex hemody... more Recent advances in 3D-PCMRI (phase contrast MRI) sequences allow for measuring the complex hemodynamics in cerebral arteries. However, the small size of these vessels vs spatial resolution can lead to non-negligible partial volume artifacts, which must be taken into account when computing blood flow rates. For this purpose, we combined the velocity information provided by 3D-PCMRI with vessel geometry measured with 3DTOF (time of flight MRI) or 3DRA (3D rotational angiography) to correct the partial volume effects in flow rate assessments. The proposed methodology was first tested in vitro on cylindrical and patient specific vessels subject to fully controlled pulsatile flows. Both 2D- and 3D-PCMRI measurements using various spatial resolutions ranging from 20 to 1.3 voxels per vessel diameter were analyzed and compared with flowmeter baseline. Second, 3DTOF, 2D- and 3D-PCMRI measurements were performed in vivo on 35 patients harboring internal carotid artery (ICA) aneurysms indicat...
Journal of neurointerventional surgery, Jan 15, 2016
Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular a... more Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning. Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) a...
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