Publications by authors named "Oliver Beuing"

42 Publications

Rupture risk assessment for multiple intracranial aneurysms: why there is no need for dozens of clinical, morphological and hemodynamic parameters.

Ther Adv Neurol Disord 2020 14;13:1756286420966159. Epub 2020 Dec 14.

Department of Neurosurgery, Otto-von-Guericke University, Magdeburg, Saxony Anhalt, Germany.

Introduction: A multitude of approaches have been postulated for assessing the risk of intracranial aneurysm rupture. However, the amount of potential predictive factors is not applicable in clinical practice and they are rejected in favor of the more practical PHASES score. For the subgroup of multiple intracranial aneurysms (MIAs), the PHASES score might severely underestimate the rupture risk, as only the aneurysm with the largest diameter is considered for risk evaluation.

Methods: In this study, we investigated 38 patients harboring a total number of 87 MIAs with respect to their morphological and hemodynamical characteristics. For the determination of the best suited parameters regarding their predictive power for aneurysm rupture, we conducted three phases of statistical evaluation. The statistical analysis aimed to identify parameters that differ significantly between ruptured and unruptured aneurysms, show smallest possible correlations among each other and have a high impact on rupture risk prediction.

Results: Significant differences between ruptured and unruptured aneurysms were found in 16 out of 49 parameters. The lowest correlation were found for gamma, aspect ratio (AR1), aneurysm maximal relative residence time (Aneurysm_RRT_max) and aneurysm mean relative residence time. The data-driven parameter selection yielded a significant correlation of only two parameters (AR1 and the Aneurysm_RRT_max) with rupture state (area under curve = 0.75).

Conclusion: A high number of established morphological and hemodynamical parameters seem to have no or only low effect on prediction of aneurysm rupture in patients with MIAs. For best possible rupture risk assessment of patients with MIAs, only the morphological parameter AR1 and the hemodynamical parameter Aneurysm_RRT_max need to be included in the prediction model.
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http://dx.doi.org/10.1177/1756286420966159DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7739206PMC
December 2020

Clinical Diffusion Mismatch to Select Pediatric Patients for Embolectomy 6 to 24 Hours After Stroke: An Analysis of the Save ChildS Study.

Neurology 2021 01 3;96(3):e343-e351. Epub 2020 Nov 3.

From the Department of Neuroradiology (P.B.S., M.-N.P., A.B.), Clinic for Radiology & Nuclear Medicine, University Hospital Basel, Switzerland; Department of Diagnostic and Interventional Neuroradiology (P.B.S., U.H., G.B., J.F.), University Medical Center Hamburg-Eppendorf, Hamburg; Departments of Pediatrics (R.S.), and Neurology (J.M.), University Hospital of Muenster; Department of Neuroradiology (R.C.), Alfried-Krupp Hospital, Essen; Department of Neuroradiology (H.H., E.H.), Klinikum Stuttgart, Germany; Department of Neuroradiology (A.G.), Medical University of Innsbruck, Austria; Department for Diagnostic and Interventional Neuroradiology (F.D.), University of Munich (LMU), Campus Grosshadern; Department of Neuroradiology (O.N., M.W.), RWTH Aachen University; Diagnostic and Interventional Neuroradiology (G.B.), Eberhard Karls University Tuebingen; Department of Radiology and Neuroradiology (A.W.), University Hospital Knappschaftskrankenhaus Bochum Langendreer; Department of Neuroradiology (D.K.), University Hospital Carl Gustav Carus, Dresden7; Department of Neuroradiology (U.Y.), Saarland University Hospital, Homburg, Germany; ASST Valcamonica (A.M.), Ospedale di Esine, UOSD Neurologia, Esine, Italy; Division of Neuroradiology and Musculoskeletal Radiology (W.M.), Department of Biomedical Imaging and Image-Guided Therapy, and Department of Biomedical Imaging and Image-Guided Therapy (R.N.), Division of Cardiovascular and Interventional Radiology, Medical University of Vienna, Austria; Department of Radiology and Neuroradiology (U.J.-K.), University Hospital of Schleswig-Holstein, Kiel; Section of Neuroradiology (M.B.), University of Ulm, Guenzburg; Department for Neuroradiology (S.S.), University Hospital Leipzig; Department of Neuroradiology (O.B.), University Hospital of Magdeburg; Department of Diagnostic and Interventional Neuroradiology (F.G.), Hannover Medical School, Germany; Institute of Neuroradiology (J.T.), Kepler University Hospital, Johannes Kepler University Linz, Austria; Institute of Neuroradiology (B.T.), University Hospital Duesseldorf; Department of Neuroradiology at Heidelberg University Hospital (M.M.); Department of Radiology (C.W.), University Hospital Regensburg; Department of Neuroradiology (P.S., A. Kemmling), University Hospital of Luebeck, Germany; Department of Neurology (P.L.M.), Massachusetts General Hospital, Harvard Medical School, Boston; Division of Child Neurology (S.L.), Department of Neurology, Stanford University, CA; Department of Neuroradiology (M.S.), University Hospital of Cologne; Department of Diagnostic and Interventional Radiology and Neuroradiology (A.R.), University Hospital Essen, University of Duisburg-Essen; Institute of Epidemiology and Social Medicine (A. Karch, N.R.), University of Muenster; and Department of Radiology, University of Munich (LMU) (M.W.), Campus Grosshadern, Germany.

Objective: To determine whether thrombectomy is safe in children up to 24 hours after onset of symptoms when selected by mismatch between clinical deficit and infarct.

Methods: A secondary analysis of the Save ChildS Study (January 2000-December 2018) was performed, including all pediatric patients (<18 years) diagnosed with arterial ischemic stroke who underwent endovascular recanalization at 27 European and United States stroke centers. Patients were included if they had a relevant mismatch between clinical deficit and infarct.

Results: Twenty children with a median age of 10.5 (interquartile range [IQR] 7-14.6) years were included. Of those, 7 were male (35%), and median time from onset to thrombectomy was 9.8 (IQR 7.8-16.2) hours. Neurologic outcome improved from a median Pediatric NIH Stroke Scale score of 12.0 (IQR 8.8-20.3) at admission to 2.0 (IQR 1.2-6.8) at day 7. Median modified Rankin Scale (mRS) score was 1.0 (IQR 0-1.6) at 3 months and 0.0 (IQR 0-1.0) at 24 months. One patient developed transient peri-interventional vasospasm; no other complications were observed. A comparison of the mRS score to the mRS score in the DAWN and DEFUSE 3 trials revealed a higher proportion of good outcomes in the pediatric compared to the adult study population.

Conclusions: Thrombectomy in pediatric ischemic stroke in an extended time window of up to 24 hours after onset of symptoms seems safe and neurologic outcomes are generally good if patients are selected by a mismatch between clinical deficit and infarct.

Classification Of Evidence: This study provides Class IV evidence that for children with acute ischemic stroke with a mismatch between clinical deficit and infarct size, thrombectomy is safe.
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http://dx.doi.org/10.1212/WNL.0000000000011107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7884981PMC
January 2021

Late sudden death following subarachnoid hemorrhage during cerebral angiography - Was vasospasm to blame?

Clin Neurol Neurosurg 2020 11 10;198:106232. Epub 2020 Sep 10.

Department of Neurosurgery, Otto-von-Guericke University, Magdeburg, Germany. Electronic address:

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http://dx.doi.org/10.1016/j.clineuro.2020.106232DOI Listing
November 2020

Derivo embolization device in the treatment of unruptured intracranial aneurysms: a prospective multicenter study.

J Neurointerv Surg 2020 Sep 8. Epub 2020 Sep 8.

Department of Intracranial Endovascular Therapy, Alfried Krupp Krankenhaus Essen, Essen, Germany.

Background: Flow diverters (FD) are used regularly for the endovascular treatment of unruptured intracranial aneurysms. We aimed to assess the safety and effectiveness of the Derivo embolization device (DED) with respect to long-term clinical and angiographic outcomes.

Methods: A prospective multicenter trial was conducted at 12 centers. Patients presenting with modified Rankin Score (mRS) of 0-1, treated for unruptured intracranial aneurysms with DED were eligible. Primary endpoint was the mRS assessed at 18 months with major morbidity defined as mRS 3-5. Satisfactory angiographic occlusion was defined as 3+4 on the Kamran scale.

Results: Between July 2014 and February 2018, 119 patients were enrolled. Twenty-three patients were excluded. Ninety-six patients, 71 (74%) female, mean age 54±12.0 years, were included in the analysis. Mean aneurysm size was 14.2±16.9 mm. The mean number of devices implanted per patient was 1.2 (range 1-3). Clinical follow-up at 18 months was available in 90 (94%) patients, resulting in a mean follow-up period of 14.8±5.2 months. At last available follow-up of 96 enrolled patients, 91 (95%) remained mRS 0-1. The major morbidity rate (mRS 3-5) was 3.1% (3/96), major stroke rate was 4.2% (4/96), and mortality was 0%. Follow-up angiographies were available in 89 (93%) patients at a median of 12.4±5.84 months with a core laboratory adjudicated satisfactory aneurysm occlusion in 89% (79/89).

Conclusion: Our results suggest that DED is a safe and effective treatment for unruptured aneurysms with high rates of satisfactory occlusion and comparably low rates of permanent neurological morbidity and mortality.

Trial Registration: DRKS00006103.
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http://dx.doi.org/10.1136/neurintsurg-2020-016303DOI Listing
September 2020

Combining visual analytics and case-based reasoning for rupture risk assessment of intracranial aneurysms.

Int J Comput Assist Radiol Surg 2020 Sep 4;15(9):1525-1535. Epub 2020 Jul 4.

Faculty of Computer Science, Otto-von-Guericke University Magdeburg, Universitätsplatz 2, D-39106, Magdeburg, Germany.

Purpose: Medical case-based reasoning solves problems by applying experience gained from the outcome of previous treatments of the same kind. Particularly for complex treatment decisions, for example, incidentally found intracranial aneurysms (IAs), it can support the medical expert. IAs bear the risk of rupture and may lead to subarachnoidal hemorrhages. Treatment needs to be considered carefully, since it may entail unnecessary complications for IAs with low rupture risk. With a rupture risk prediction based on previous cases, the treatment decision can be supported.

Methods: We present an interactive visual exploration tool for the case-based reasoning of IAs. In presence of a new aneurysm of interest, our application provides visual analytics techniques to identify the most similar cases with respect to morphology. The clinical expert can obtain the treatment, including the treatment outcome, for these cases and transfer it to the aneurysm of interest. Our application comprises a heatmap visualization, an adapted scatterplot matrix and fully or partially directed graphs with a circle- or force-directed layout to guide the interactive selection process. To fit the demands of clinical applications, we further integrated an interactive identification of outlier cases as well as an interactive attribute selection for the similarity calculation. A questionnaire evaluation with six trained physicians was used.

Result: Our application allows for case-based reasoning of IAs based on a reference data set. Three classifiers summarize the rupture state of the most similar cases. Medical experts positively evaluated the application.

Conclusion: Our case-based reasoning application combined with visual analytic techniques allows for representation of similar IAs to support the clinician. The graphical representation was rated very useful and provides visual information of the similarity of the k most similar cases.
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http://dx.doi.org/10.1007/s11548-020-02217-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7420879PMC
September 2020

Does Device Selection Impact Recanalization Rate and Neurological Outcome?: An Analysis of the Save ChildS Study.

Stroke 2020 04 2;51(4):1182-1189. Epub 2020 Mar 2.

Institute of Neuroradiology, University Hospital Duesseldorf, Germany (B.T.).

Background and Purpose- The recent Save ChildS study provides multicenter evidence for the use of mechanical thrombectomy in children with large vessel occlusion arterial ischemic stroke. However, device selection for thrombectomy may influence rates of recanalization, complications, and neurological outcomes, especially in pediatric patients of different ages. We, therefore, performed additional analyses of the Save ChildS data to investigate a possible association of different thrombectomy techniques and devices with angiographic and clinical outcome parameters. Methods- The Save ChildS cohort study (January 2000-December 2018) analyzed data from 27 European and United States stroke centers and included all pediatric patients (<18 years), diagnosed with arterial ischemic stroke who underwent endovascular recanalization. Patients were grouped into first-line contact aspiration (A Direct Aspiration First Pass Technique [ADAPT]) and non-ADAPT groups as well as different stent retriever size groups. Associations with baseline characteristics, recanalization rates (modified Treatment in Cerebral Infarction), complication rates, and neurological outcome parameters (Pediatric National Institutes of Health Stroke Scale after 24 hours and 7 days; modified Rankin Scale and Pediatric Stroke Outcome Measure at discharge, after 6 and 24 months) were investigated. Results- Seventy-three patients with a median age of 11.3 years were included. Currently available stent retrievers were used in 59 patients (80.8%), of which 4×20 mm (width×length) was the most frequently chosen size (36 patients =61%). A first-line ADAPT approach was used in 7 patients (9.6%), and 7 patients (9.6%) were treated with first-generation thrombectomy devices. In this study, a first-line ADAPT approach was neither associated with the rate of successful recanalization (ADAPT 85.7% versus 87.5% No ADAPT) nor with the complication rate or the neurological outcome. Moreover, there were no associations of stent retriever sizes with rates of recanalization, complication rates, or outcome parameters. Conclusions- Our study suggests that neurological outcomes are generally good regardless of any specific device selection and suggests that it is important to offer thrombectomy in eligible children regardless of technique or device selection. Registration- URL: https://www.drks.de/; Unique identifier: DRKS00016528.
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http://dx.doi.org/10.1161/STROKEAHA.119.028221DOI Listing
April 2020

Stent-assisted coiling of broad-necked intracranial aneurysms with a new braided microstent (Accero): procedural results and long-term follow-up.

Sci Rep 2020 01 15;10(1):412. Epub 2020 Jan 15.

Department of Neuroradiology, University Hospital Magdeburg, Leipziger Str. 44, Magdeburg, Germany.

Intracranial stents have expanded endovascular therapy options for intracranial aneurysms. The braided Accero stent is available for clinical use since May 2015. To date, no clinical reports on the stent are available. Purpose of this study was the evaluation of the safety and efficacy of the Accero stent in stent-assisted coiling. All patients, in whom implantation of the stent was performed, were included. Primary endpoints were good clinical outcome (mRS ≤ 2) and aneurysm occlusion grades 1 and 2 (Raymond Roy Occlusion Classification). Secondary endpoints were procedural and device-related complications with permanent disability or death, complications in the course, and the recanalization rate. Between September 2015 and August 2018, thirty-four aneurysms were treated with stent-assisted coiling using the Accero. Sixteen aneurysms were untreated, four of these were ruptured. Mild neurological complications occurred in 2/34 (5.9%) treatments. Two stent occlusions occurred during follow-up. No patient had a poor procedure- or device-related outcome. After an average of 15 months of follow-up, 28/30 aneurysms were completely or near-completely occluded. The Accero stent proved to be safe and effective in the treatment of broad-based intracranial aneurysms. The complication rate and the rate of successful aneurysm occlusions are similar to those of other stents.
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http://dx.doi.org/10.1038/s41598-019-57102-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6962445PMC
January 2020

Reduction of beam hardening artifacts on real C-arm CT data using polychromatic statistical image reconstruction.

Z Med Phys 2020 Feb 9;30(1):40-50. Epub 2019 Dec 9.

Otto-von-Guericke-University Magdeburg, Institute for Medical Engineering, Germany.

Purpose: This work aims at the compensation of beam hardening artifacts by the means of an extended three-dimensional polychromatic statistical reconstruction to be applied for flat panel cone-beam CT.

Methods: We implemented this reconstruction technique as being introduced by Elbakri et al. (2002) [1] for a multi-GPU system, assuming the underlying object consists of several well-defined materials. Furthermore, we assume one voxel can only contain an overlap of at most two materials, depending on its density value. Given the X-ray spectrum, the procedure enables to reconstruct the energy-dependent attenuation values of the volume.

Results: We evaluated the method by using flat-panel cone-beam CT measurements of structures containing small metal objects and clinical head scan data. In comparison with the water-corrected filtered backprojection, as well as a maximum likelihood reconstruction with a consistency-based beam hardening correction, our method features clearly reduced beam hardening artifacts and a more accurate shape of metal objects.

Conclusions: Our multi-GPU implementation of the polychromatic reconstruction, which does not require any image pre-segmentation, clearly outperforms the standard reconstructions of objects, with respect to beam hardening even in the presence of metal objects inside the volume. However, remaining artifacts, caused mainly by the limited dynamic range of the detector, may have to be addressed in future work.
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http://dx.doi.org/10.1016/j.zemedi.2019.10.002DOI Listing
February 2020

Feasibility, Safety, and Outcome of Endovascular Recanalization in Childhood Stroke: The Save ChildS Study.

JAMA Neurol 2020 01;77(1):25-34

Institute of Neuroradiology, University Hospital Duesseldorf, Duesseldorf, Germany.

Importance: Randomized clinical trials have shown the efficacy of thrombectomy of large intracranial vessel occlusions in adults; however, any association of therapy with clinical outcomes in children is unknown.

Objective: To evaluate the use of endovascular recanalization in pediatric patients with arterial ischemic stroke.

Design, Setting, And Participants: This retrospective, multicenter cohort study, conducted from January 1, 2000, to December 31, 2018, analyzed the databases from 27 stroke centers in Europe and the United States. Included were all pediatric patients (<18 years) with ischemic stroke who underwent endovascular recanalization. Median follow-up time was 16 months.

Exposures: Endovascular recanalization.

Main Outcomes And Measures: The decrease of the Pediatric National Institutes of Health Stroke Scale (PedNIHSS) score from admission to day 7 was the primary outcome (score range: 0 [no deficit] to 34 [maximum deficit]). Secondary clinical outcomes included the modified Rankin scale (mRS) (score range: 0 [no deficit] to 6 [death]) at 6 and 24 months and rate of complications.

Results: Seventy-three children from 27 participating stroke centers were included. Median age was 11.3 years (interquartile range [IQR], 7.0-15.0); 37 patients (51%) were boys, and 36 patients (49%) were girls. Sixty-three children (86%) received treatment for anterior circulation occlusion and 10 patients (14%) received treatment for posterior circulation occlusion; 16 patients (22%) received concomitant intravenous thrombolysis. Neurologic outcome improved from a median PedNIHSS score of 14.0 (IQR, 9.2-20.0) at admission to 4.0 (IQR, 2.0-7.3) at day 7. Median mRS score was 1.0 (IQR, 0-1.6) at 6 months and 1.0 (IQR, 0-1.0) at 24 months. One patient (1%) developed a postinterventional bleeding complication and 4 patients (5%) developed transient peri-interventional vasospasm. The proportion of symptomatic intracerebral hemorrhage events in the HERMES meta-analysis of trials with adults was 2.79 (95% CI, 0.42-6.66) and in Save ChildS was 1.37 (95% CI, 0.03-7.40).

Conclusions And Relevance: The results of this study suggest that the safety profile of thrombectomy in childhood stroke does not differ from the safety profile in randomized clinical trials for adults; most of the treated children had favorable neurologic outcomes. This study may support clinicians' practice of off-label thrombectomy in childhood stroke in the absence of high-level evidence.
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http://dx.doi.org/10.1001/jamaneurol.2019.3403DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6802048PMC
January 2020

Deployment of flow diverter devices: prediction of foreshortening and validation of the simulation in 18 clinical cases.

Neuroradiology 2019 Nov 31;61(11):1319-1326. Epub 2019 Aug 31.

Department of Neuroradiology, Otto-von-Guericke University Magdeburg, Leipziger Straße 44, 39112, Magdeburg, Germany.

Purpose: Flow diverter (FD) devices show severe shortening during deployment in dependency of the vessel geometry. Valid information regarding the geometry of the targeted vessel is therefore mandatory for correct device selection, and to avoid complications. But the geometry of diseased tortuous intracranial vessels cannot be measured accurately with standard methods. The goal of this study is to prove the accuracy of a novel virtual stenting method in prediction of the behavior of a FD in an individual vessel geometry.

Methods: We applied a virtual stenting method on angiographic 3D imaging data of the specific vasculature of patients, who underwent FD treatment. The planning tool analyzes the local vessel morphology and deploys the FD virtually. We measured in 18 cases the difference between simulated FD length and real FD length after treatment in a landmark-based registration of pre-/post-interventional 3D angiographic datasets.

Results: The mean value of length deviation of the virtual FD was 2.2 mm (SD ± 1.9 mm) equaling 9.5% (SD ± 8.2%). Underestimated cases present lower deviations compared with overestimated FDs. Flow diverter cases with a nominal device length of 20 mm had the highest prediction accuracy.

Conclusion: The results suggest that the virtual stenting method used in this study is capable of predicting FD length with a clinically sufficient accuracy in advance and could therefore be a helpful tool in intervention planning. Imaging data of high quality are mandatory, while processing and manipulation of the FD during the intervention may impact the accuracy.
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http://dx.doi.org/10.1007/s00234-019-02287-wDOI Listing
November 2019

Resolution of Brainstem Edema after Neurosurgical Occlusion of Dural Arteriovenous Fistulas of the Craniocervical Junction: Report of Three Cases and Review.

J Neurol Surg A Cent Eur Neurosurg 2020 Jan 29;81(1):80-85. Epub 2019 Aug 29.

Klinik für Neuroradiologie, Otto-von-Guericke-Universität Magdeburg, Sachsen-Anhalt, Germany.

Objective:  Dural arteriovenous fistulas of the craniocervical junction are rare but the most dangerous of spinal fistulas. The concurrent brainstem edema has been attributed to increased pressure within the venous outflow of the brainstem and upper cord, but the differential diagnosis of brainstem edema is demanding. This report presents the details of clinical findings, magnetic resonance imaging (MRI) , surgical techniques, and follow-up of these fistulas.

Methods:  Three cases with dural arteriovenous fistulas and edema of the brainstem and upper cord are described plus a review of the literature. Clinical presentation, radiologic findings, and a follow-up of outcomes are presented.

Results:  All three cases with misleading diagnoses at the time of referral experienced variable degrees of tetraparesis with brainstem edema on MRI. Congested veins on MRI raised the suspicion of a vascular origin of the edema. The diagnosis was established with highly specific angiography with microcatheters identifying a feeder from the ascending pharyngeal artery in two cases and a tentorial feeder from the carotid artery in one case. The operation included temporary clipping of the fistula and neuromonitoring. Follow-up confirmed improvement of clinical signs and resolution of the brainstem edema on MRI.

Conclusion:  Edema of the brainstem and cervical cord may be caused by a dural arteriovenous fistula of the craniocervical junction. Surgical occlusion may be an efficient option for the complete resolution of radiologic and clinical symptoms.
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http://dx.doi.org/10.1055/s-0039-1688560DOI Listing
January 2020

Flow-splitting-based computation of outlet boundary conditions for improved cerebrovascular simulation in multiple intracranial aneurysms.

Int J Comput Assist Radiol Surg 2019 Oct 30;14(10):1805-1813. Epub 2019 Jul 30.

Department of Fluid Dynamics and Technical Flows, Otto-von-Guericke University Magdeburg, Universitätsplatz 2, 39106, Magdeburg, Germany.

Purpose: Image-based hemodynamic simulations have great potential for precise blood flow predictions in intracranial aneurysms. Due to model assumptions and simplifications with respect to boundary conditions, clinical acceptance remains limited.

Methods: Within this study, we analyzed the influence of outflow-splitting approaches on multiple aneurysm studies and present a new outflow-splitting approach that takes the precise morphological vessel cross sections into account. We provide a detailed comparison of five outflow strategies considering eight intracranial aneurysms: zero-pressure configuration (1), a flow splitting inspired by Murray's law with a square (2) and a cubic (3) vessel diameter, a flow splitting incorporating vessel bifurcations based on circular vessel cross sections (4) and our novel flow splitting including vessel bifurcations and anatomical vessel cross sections (5). Other boundary conditions remain constant. For each simulation and each aneurysm, we conducted an evaluation based on common hemodynamic parameters, e.g., normalized wall shear stress and inflow concentration index.

Results: The comparison of five outflow strategies for image-based simulations shows a large variability regarding the parameters of interest. Qualitatively, our strategy based on anatomical cross sections yields a more uniform flow rate distribution with increased aneurysm inflow rates. The commonly used zero-pressure approach shows the largest variations, especially for more distal aneurysms. A rank ordering of multiple aneurysms in one patient might still be possible, since the ordering appeared to be independent of the outflow strategy.

Conclusions: The results reveal that outlet boundary conditions have a crucial impact on image-based blood flow simulations, especially for multiple aneurysm studies. We could confirm the advantages of the more complex outflow-splitting model (4) including an incremental improvement (5) compared to strategies (1), (2) and (3) for this application scenario. Furthermore, we discourage from using zero-pressure configurations that lack a physiological basis.
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http://dx.doi.org/10.1007/s11548-019-02036-7DOI Listing
October 2019

Stent-induced vessel deformation after intracranial aneurysm treatment - A hemodynamic pilot study.

Comput Biol Med 2019 08 20;111:103338. Epub 2019 Jun 20.

Forschungscampus STIMULATE, University of Magdeburg, Sandtorstraße 23, 39106, Magdeburg, Germany; Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Universitaetsplatz 2, 39106, Magdeburg, Germany.

Background: Stent-assisted coiling has become an important treatment option for intracranial aneurysms. However, studies have shown that this procedure can lead to the deformation of the local vasculature. Its effect on intra-aneurysmal hemodynamics still remains unclear.

Methods: Pre- and post-interventional image data of three representative middle cerebral artery aneurysms are considered in this study. This includes virtually deployed stents and coils. To evaluate the proportional effect of a) vessel deformation, b) stent deployment, and c) coil placement, 24 unsteady blood flow simulations were carried out focusing on the separated effects related to intra-aneurysmal hemodynamics. Four flow parameters (velocity within the aneurysm sac, aneurysm neck inflow rate, inflow concentration index, and ostium inflow area) and four shear parameters (wall shear stress, normalized wall shear stress, shear concentration index, and high shear area) were quantified.

Results: All of the considered flow and shear parameters, except for the shear concentration index, were clearly reduced due to treatment. Coiling and stenting caused a distinct and smaller neck inflow rate, respectively, while the impact of deformation was inconsistent among the aneurysms. Overall, coiling appears to have the strongest impact on local hemodynamics.

Conclusion: Stent-induced vessel deformation has a clear impact on intra-aneurysmal hemodynamics. This effect is neglected by the majority of previous studies, which consider the pre-interventional state for investigating the relation of stents and hemodynamics. The findings of this pilot study suggest that while stent-assisted coiling can lead to an improved hemodynamic situation, undesired flow conditions may occur in response to treatment.
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http://dx.doi.org/10.1016/j.compbiomed.2019.103338DOI Listing
August 2019

A review on the reliability of hemodynamic modeling in intracranial aneurysms: why computational fluid dynamics alone cannot solve the equation.

Neurosurg Focus 2019 07;47(1):E15

1Department of Fluid Dynamics and Technical Flows.

Computational blood flow modeling in intracranial aneurysms (IAs) has enormous potential for the assessment of highly resolved hemodynamics and derived wall stresses. This results in an improved knowledge in important research fields, such as rupture risk assessment and treatment optimization. However, due to the requirement of assumptions and simplifications, its applicability in a clinical context remains limited.This review article focuses on the main aspects along the interdisciplinary modeling chain and highlights the circumstance that computational fluid dynamics (CFD) simulations are embedded in a multiprocess workflow. These aspects include imaging-related steps, the setup of realistic hemodynamic simulations, and the analysis of multidimensional computational results. To condense the broad knowledge, specific recommendations are provided at the end of each subsection.Overall, various individual substudies exist in the literature that have evaluated relevant technical aspects. In this regard, the importance of precise vessel segmentations for the simulation outcome is emphasized. Furthermore, the accuracy of the computational model strongly depends on the specific research question. Additionally, standardization in the context of flow analysis is required to enable an objective comparison of research findings and to avoid confusion within the medical community. Finally, uncertainty quantification and validation studies should always accompany numerical investigations.In conclusion, this review aims for an improved awareness among physicians regarding potential sources of error in hemodynamic modeling for IAs. Although CFD is a powerful methodology, it cannot provide reliable information, if pre- and postsimulation steps are inaccurately carried out. From this, future studies can be critically evaluated and real benefits can be differentiated from results that have been acquired based on technically inaccurate procedures.
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http://dx.doi.org/10.3171/2019.4.FOCUS19181DOI Listing
July 2019

CSF Neurofilament light chain level predicts axonal damage in cerebral vasculitis.

Ann Clin Transl Neurol 2019 Jun 3;6(6):1134-1137. Epub 2019 Jun 3.

Department of Neurology Otto-von-Guericke University Leipziger Straße 44 39120 Magdeburg Germany.

The rarity of primary angiitis of the central nervous system (PACNS) demands diagnostic and prognostic biomarkers. We retrospectively measured Neurofilament light chain (NFL) concentrations in cerebrospinal fluid in a severely relapsing PACNS patient at multiple time points during the course of the disease. A marked increase in NFL levels preceding the onset of neuro-axonal damage and arterial-vessel abnormalities was observed with magnetic resonance imaging as well as with MR- and conventional angiography. Thus, marked elevation of NFL in PACNS seems to occur ahead of definitive radiological abnormalities and might serve as a diagnostic biomarker.
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http://dx.doi.org/10.1002/acn3.790DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562033PMC
June 2019

Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH)-Phase Ib: Effect of morphology on hemodynamics.

PLoS One 2019 17;14(5):e0216813. Epub 2019 May 17.

Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany.

Background: Image-based blood flow simulations have been increasingly applied to investigate intracranial aneurysm (IA) hemodynamics. However, the acceptance among physicians remains limited due to the high variability in the underlying assumptions and quality of results.

Methods: To evaluate the vessel segmentation as one of the most important sources of error, the international Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH) was announced. 26 research groups from 13 different countries segmented three datasets, which contained five IAs in total. Based on these segmentations, 73 time-dependent blood flow simulations under consistent conditions were carried out. Afterwards, relevant flow and shear parameters (e.g., neck inflow rate, parent vessel flow rate, spatial mean velocity, and wall shear stress) were analyzed both qualitatively and quantitatively.

Results: Regarding the entire vasculature, the variability of the segmented vessel radius is 0.13 mm, consistent and independent of the local vessel radius. However, the centerline velocity shows increased variability in more distal vessels. Focusing on the aneurysms, clear differences in morphological and hemodynamic parameters were observed. The quantification of the segmentation-induced variability showed approximately a 14% difference among the groups for the parent vessel flow rate. Regarding the mean aneurysmal velocity and the neck inflow rate, a variation of 30% and 46% was observed, respectively. Finally, time-averaged wall shear stresses varied between 28% and 51%, depending on the aneurysm in question.

Conclusions: MATCH reveals the effect of state-of-the-art segmentation algorithms on subsequent hemodynamic simulations for IA research. The observed variations may lead to an inappropriate interpretation of the simulation results and thus, can lead to inappropriate conclusions by physicians. Therefore, accurate segmentation of the region of interest is necessary to obtain reliable and clinically helpful flow information.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216813PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6524809PMC
January 2020

Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH)-phase II: rupture risk assessment.

Int J Comput Assist Radiol Surg 2019 Oct 3;14(10):1795-1804. Epub 2019 May 3.

Christian-Albrechts-University, Kiel, Germany.

Purpose: Assessing the rupture probability of intracranial aneurysms (IAs) remains challenging. Therefore, hemodynamic simulations are increasingly applied toward supporting physicians during treatment planning. However, due to several assumptions, the clinical acceptance of these methods remains limited.

Methods: To provide an overview of state-of-the-art blood flow simulation capabilities, the Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH) was conducted. Seventeen research groups from all over the world performed segmentations and hemodynamic simulations to identify the ruptured aneurysm in a patient harboring five IAs. Although simulation setups revealed good similarity, clear differences exist with respect to the analysis of aneurysm shape and blood flow results. Most groups (12/71%) included morphological and hemodynamic parameters in their analysis, with aspect ratio and wall shear stress as the most popular candidates, respectively.

Results: The majority of groups (7/41%) selected the largest aneurysm as being the ruptured one. Four (24%) of the participating groups were able to correctly select the ruptured aneurysm, while three groups (18%) ranked the ruptured aneurysm as the second most probable. Successful selections were based on the integration of clinically relevant information such as the aneurysm site, as well as advanced rupture probability models considering multiple parameters. Additionally, flow characteristics such as the quantification of inflow jets and the identification of multiple vortices led to correct predictions.

Conclusions: MATCH compares state-of-the-art image-based blood flow simulation approaches to assess the rupture risk of IAs. Furthermore, this challenge highlights the importance of multivariate analyses by combining clinically relevant metadata with advanced morphological and hemodynamic quantification.
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http://dx.doi.org/10.1007/s11548-019-01986-2DOI Listing
October 2019

Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH): uncertainty quantification of geometric rupture risk parameters.

Biomed Eng Online 2019 Mar 25;18(1):35. Epub 2019 Mar 25.

Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany.

Background: Geometric parameters have been proposed for prediction of cerebral aneurysm rupture risk. Predicting the rupture risk for incidentally detected unruptured aneurysms could help clinicians in their treatment decision. However, assessment of geometric parameters depends on several factors, including the spatial resolution of the imaging modality used and the chosen reconstruction procedure. The aim of this study was to investigate the uncertainty of a variety of previously proposed geometric parameters for rupture risk assessment, caused by variability of reconstruction procedures.

Materials: 26 research groups provided segmentations and surface reconstructions of five cerebral aneurysms as part of the Multiple Aneurysms AnaTomy CHallenge (MATCH) 2018. 40 dimensional and non-dimensional geometric parameters, describing aneurysm size, neck size, and irregularity of aneurysm shape, were computed. The medians as well as the absolute and relative uncertainties of the parameters were calculated. Additionally, linear regression analysis was performed on the absolute uncertainties and the median parameter values.

Results: A large variability of relative uncertainties in the range between 3.9 and 179.8% was found. Linear regression analysis indicates that some parameters capture similar geometric aspects. The lowest uncertainties < 6% were found for the non-dimensional parameters isoperimetric ratio, convexity ratio, and ellipticity index. Uncertainty of 2D and 3D size parameters was significantly higher than uncertainty of 1D parameters. The most extreme uncertainties > 80% were found for some curvature parameters.

Conclusions: Uncertainty analysis is essential on the road to clinical translation and use of rupture risk prediction models. Uncertainty quantification of geometric rupture risk parameters provided by this study may help support development of future rupture risk prediction models.
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http://dx.doi.org/10.1186/s12938-019-0657-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6434802PMC
March 2019

3DRA Reconstruction of Intracranial Aneurysms - How does Voxel Size Influences Morphologic and Hemodynamic Parameters.

Annu Int Conf IEEE Eng Med Biol Soc 2018 Jul;2018:1327-1330

Three-dimensional shape analysis and imagebased hemodynamic simulations are widely used to assess the individual rupture risk of intracranial aneurysms. However, the quality of those results highly depends on pre-simulative working steps including image reconstruction and segmentation. Within this study, three patient-specific aneurysms were reconstructed using three different voxel sizes (0.1 mm, 0.3 mm, 0.5 mm). Afterwards, 3D segmentations and time-dependent blood flow simulations were carried out to evaluate the impact of the reconstruction size. The results indicate that overall all voxel sizes lead to a qualitatively good agreement with respect to the aneurysm surfaces. However, deviations occur regarding the neck representation as well as the consideration of perforating arteries. Further, morphological differences lead to clear hemodynamic variations, especially for shear force predictions. The findings indicate that depending on the desired analysis, careful reconstruction parameter selection is required. Particularly, for quantitative morphology and blood flow studies, the early step of reconstruction can have a crucial effect on subsequent results.
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http://dx.doi.org/10.1109/EMBC.2018.8512524DOI Listing
July 2018

Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH): Phase I: Segmentation.

Cardiovasc Eng Technol 2018 12 6;9(4):565-581. Epub 2018 Sep 6.

Stanford University, Stanford, CA, USA.

Purpose: Advanced morphology analysis and image-based hemodynamic simulations are increasingly used to assess the rupture risk of intracranial aneurysms (IAs). However, the accuracy of those results strongly depends on the quality of the vessel wall segmentation.

Methods: To evaluate state-of-the-art segmentation approaches, the Multiple Aneurysms AnaTomy CHallenge (MATCH) was announced. Participants carried out segmentation in three anonymized 3D DSA datasets (left and right anterior, posterior circulation) of a patient harboring five IAs. Qualitative and quantitative inter-group comparisons were carried out with respect to aneurysm volumes and ostia. Further, over- and undersegmentation were evaluated based on highly resolved 2D images. Finally, clinically relevant morphological parameters were calculated.

Results: Based on the contributions of 26 participating groups, the findings reveal that no consensus regarding segmentation software or underlying algorithms exists. Qualitative similarity of the aneurysm representations was obtained. However, inter-group differences occurred regarding the luminal surface quality, number of vessel branches considered, aneurysm volumes (up to 20%) and ostium surface areas (up to 30%). Further, a systematic oversegmentation of the 3D surfaces was observed with a difference of approximately 10% to the highly resolved 2D reference image. Particularly, the neck of the ruptured aneurysm was overrepresented by all groups except for one. Finally, morphology parameters (e.g., undulation and non-sphericity) varied up to 25%.

Conclusions: MATCH provides an overview of segmentation methodologies for IAs and highlights the variability of surface reconstruction. Further, the study emphasizes the need for careful processing of initial segmentation results for a realistic assessment of clinically relevant morphological parameters.
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http://dx.doi.org/10.1007/s13239-018-00376-0DOI Listing
December 2018

Semiautomatic neck curve reconstruction for intracranial aneurysm rupture risk assessment based on morphological parameters.

Int J Comput Assist Radiol Surg 2018 Nov 29;13(11):1781-1793. Epub 2018 Aug 29.

Department of Neuroradiology, University Hospital of Magdeburg, Magdeburg, Germany.

Purpose: Morphological parameters of intracranial aneurysms (IAs) are well established for rupture risk assessment. However, a manual measurement is error-prone, not reproducible and cumbersome. For an automatic extraction of morphological parameters, a 3D neck curve reconstruction approach to delineate the aneurysm from the parent vessel is required.

Methods: We present a 3D semiautomatic aneurysm neck curve reconstruction for the automatic extraction of morphological parameters which was developed and evaluated with an experienced neuroradiologist. We calculate common parameters from the literature and include two novel angle-based parameters: the characteristic dome point angle and the angle difference of base points.

Results: We applied our method to 100 IAs acquired with rotational angiography in clinical routine. For validation, we compared our approach to manual segmentations yielding highly significant correlations. We analyzed 95 of these datasets regarding rupture state. Statistically significant differences were found in ruptured and unruptured groups for maximum diameter, maximum height, aspect ratio and the characteristic dome point angle. These parameters were also found to statistically significantly correlate with each other.

Conclusions: The new 3D neck curve reconstruction provides robust results for all datasets. The reproducibility depends on the vessel tree centerline and the user input for the initial dome point and parameters characterizing the aneurysm neck region. The characteristic dome point angle as a new metric regarding rupture risk assessment can be extracted. It requires less computational effort than the complete neck curve reconstruction.
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http://dx.doi.org/10.1007/s11548-018-1848-xDOI Listing
November 2018

Comparison of intracranial aneurysm flow quantification techniques: standard PIV vs stereoscopic PIV vs tomographic PIV vs phase-contrast MRI vs CFD.

J Neurointerv Surg 2019 Mar 30;11(3):275-282. Epub 2018 Jul 30.

Department of Fluid Dynamics and Technical Flows, Otto von Guericke Universität Magdeburg, Magdeburg, Germany.

Image-based hemodynamic simulations to assess the rupture risk or improve the treatment planning of intracranial aneurysms have become popular recently. However, due to strong modeling assumptions and limitations, the acceptance of numerical approaches remains limited. Therefore, validation using experimental methods is mandatory.In this study, a unique compilation of four in-vitro flow measurements (three particle image velocimetry approaches using a standard (PIV), stereoscopic (sPIV), and tomographic (tPIV) setup, as well as a phase-contrast magnetic resonance imaging (PC-MRI) measurement) were compared with a computational fluid dynamics (CFD) simulation. This was carried out in a patient-specific silicone phantom model of an internal carotid artery aneurysm under steady flow conditions. To evaluate differences between each technique, a similarity index (SI) with respect to the velocity vectors and the average velocity magnitude differences among all involved modalities were computed.The qualitative comparison reveals that all techniques are able to provide a reasonable description of the global flow structures. High quantitative agreement in terms of SI and velocity magnitude differences was found between all PIV methods and CFD. However, quantitative differences were observed between PC-MRI and the other techniques. Deeper analysis revealed that the limited resolution of the PC-MRI technique is a major contributor to the experienced differences and leads to a systematic underestimation of overall velocity magnitude levels inside the vessel. This confirms the necessity of using highly resolving flow measurement techniques, such as PIV, in an in-vitro environment to individually verify the validity of the numerically obtained hemodynamic results.
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http://dx.doi.org/10.1136/neurintsurg-2018-013921DOI Listing
March 2019

Classification of Blood Flow Patterns in Cerebral Aneurysms.

IEEE Trans Vis Comput Graph 2019 07 15;25(7):2404-2418. Epub 2018 May 15.

We present a Cerebral Aneurysm Vortex Classification (CAVOCLA) that allows to classify blood flow in cerebral aneurysms. Medical studies assume a strong relation between the progression and rupture of aneurysms and flow patterns. To understand how flow patterns impact the vessel morphology, they are manually classified according to predefined classes. However, manual classifications are time-consuming and exhibit a high inter-observer variability. In contrast, our approach is more objective and faster than manual methods. The classification of integral lines, representing steady or unsteady blood flow, is based on a mapping of the aneurysm surface to a hemisphere by calculating polar-based coordinates. The lines are clustered and for each cluster a representative is calculated. Then, the polar-based coordinates are transformed to the representative as basis for the classification. Classes are based on the flow complexity. The classification results are presented by a detail-on-demand approach using a visual transition from the representative over an enclosing surface to the associated lines. Based on seven representative datasets, we conduct an informal interview with five domain experts to evaluate the system. They confirmed that CAVOCLA allows for a robust classification of intra-aneurysmal flow patterns. The detail-on-demand visualization enables an efficient exploration and interpretation of flow patterns.
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http://dx.doi.org/10.1109/TVCG.2018.2834923DOI Listing
July 2019

Beam Hardening Correction Using Cone Beam Consistency Conditions.

IEEE Trans Med Imaging 2018 10 24;37(10):2266-2277. Epub 2018 May 24.

The polychromatic X-ray spectrum and the energy-dependent attenuation coefficient of materials cause beam hardening artifacts in CT reconstructed volumes. These artifacts appear as cupping and streak artifacts depending on the material composition and the geometry of the imaged object. CT scanners employ projection linearization to transform polychromatic attenuation to monochromatic attenuation using a polynomial model. Polynomial coefficients are computed during calibration or using prior information such as X-ray spectrum and attenuation properties of the materials. In this paper, we are presenting a novel method to correct beam hardening artifacts by enforcing cone beam consistency conditions on the projection data. We used consistency conditions derived from Grangeat's fundamental relation between cone beam projection data and 3-D Radon transform. The optimal polynomial coefficients for artifact reduction are iteratively estimated by minimizing the inconsistency of a set of projection pairs. The results from simulated and real datasets show the visible reduction of artifacts. Our studies also demonstrate the robustness of the algorithm when the projections are perturbed with other physical measurement and geometrical errors. The proposed method requires neither calibration nor prior information like X-ray spectrum, attenuation properties of the materials and detector response. The algorithm can be used for beam hardening correction in clinical, pre-clinical, and industrial CT systems.
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http://dx.doi.org/10.1109/TMI.2018.2840343DOI Listing
October 2018

Clinical and experimental evidence suggest a link between KIF7 and C5orf42-related ciliopathies through Sonic Hedgehog signaling.

Eur J Hum Genet 2018 02 10;26(2):197-209. Epub 2018 Jan 10.

Institute of Medical Genetics, University of Zurich, Schlieren-Zurich, Switzerland.

Acrocallosal syndrome (ACLS) is an autosomal recessive neurodevelopmental disorder caused by KIF7 defects and belongs to the heterogeneous group of ciliopathies related to Joubert syndrome (JBTS). While ACLS is characterized by macrocephaly, prominent forehead, depressed nasal bridge, and hypertelorism, facial dysmorphism has not been emphasized in JBTS cohorts with molecular diagnosis. To evaluate the specificity and etiology of ACLS craniofacial features, we performed whole exome or targeted Sanger sequencing in patients with the aforementioned overlapping craniofacial appearance but variable additional ciliopathy features followed by functional studies. We found (likely) pathogenic variants of KIF7 in 5 out of 9 families, including the original ACLS patients, and delineated 1000 to 4000-year-old Swiss founder alleles. Three of the remaining families had (likely) pathogenic variants in the JBTS gene C5orf42, and one patient had a novel de novo frameshift variant in SHH known to cause autosomal dominant holoprosencephaly. In accordance with the patients' craniofacial anomalies, we showed facial midline widening after silencing of C5orf42 in chicken embryos. We further supported the link between KIF7, SHH, and C5orf42 by demonstrating abnormal primary cilia and diminished response to a SHH agonist in fibroblasts of C5orf42-mutated patients, as well as axonal pathfinding errors in C5orf42-silenced chicken embryos similar to those observed after perturbation of Shh signaling. Our findings, therefore, suggest that beside the neurodevelopmental features, macrocephaly and facial widening are likely more general signs of disturbed SHH signaling. Nevertheless, long-term follow-up revealed that C5orf42-mutated patients showed catch-up development and fainting of facial features contrary to KIF7-mutated patients.
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http://dx.doi.org/10.1038/s41431-017-0019-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5839020PMC
February 2018

Multiple intracranial aneurysms: a direct hemodynamic comparison between ruptured and unruptured vessel malformations.

Int J Comput Assist Radiol Surg 2018 Jan 21;13(1):83-93. Epub 2017 Jul 21.

Institute of Neuroradiology, University Hospital Magdeburg, Leipziger Str. 44, 39120, Magdeburg, Germany.

Purpose: Despite numerous studies addressing the rupture risk of intracranial aneurysms that have been published, the assessment thereof still remains challenging. Image-based simulations enable a precise prediction of patient-specific blood flow information. However, those approaches normally consider only small segments of the complete cerebral vasculature.

Methods: To test the validity of the consideration of single aneurysms in one computational setup, domains of the complete anterior and posterior circulations with multiple intracranial aneurysms (MIA) were simulated. Six patients with MIA were investigated, while 3D surfaces of eleven unruptured and six ruptured aneurysms were segmented. The segmentations were used for the determination of morphological parameters and also for image-based blood flow simulations used to characterize the hemodynamic properties of each aneurysm.

Results: In the geometric comparison, neck aspect ratios of unruptured and ruptured aneurysms did not differ significantly. In contrast, size ratios, aspect ratios, surface areas, volumes, and non-sphericity indices were significantly higher in the ruptured cases. The analysis of hemodynamic parameters demonstrated that in each patient, the ruptured aneurysm exhibited the lowest averaged wall shear stresses and highest oscillatory shears. Unstable flow was also detected in ruptured aneurysms based on increased oscillatory velocity.

Conclusion: In this small study involving patients with MIA, different morphologies and flow patterns were observed between ruptured and unruptured aneurysms. The analysis of the hemodynamics in such patients revealed a good agreement with studies that only considered single malformations. Additionally, complex flow patterns are detected in ruptured cases, which require deeper investigation.
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http://dx.doi.org/10.1007/s11548-017-1643-0DOI Listing
January 2018

Bringing hemodynamic simulations closer to the clinics: a CFD prototype study for intracranial aneurysms.

Annu Int Conf IEEE Eng Med Biol Soc 2016 Aug;2016:3302-3305

Computational Fluid Dynamics enables the investigation of patient-specific hemodynamics for rupture predictions and treatment support of intracranial aneurysms. However, due to numerous simplifications to decrease the computations effort, clinical applicability is limited until now. To overcome this situation a clinical research software prototype was tested that can be easily operated by attending physicians. In order to evaluate the accuracy of this prototype, four patient-specific intracranial aneurysms were investigated using four different spatial resolutions. The results demonstrate that physicians were able to generate hemodynamic predictions within several minutes at low spatial resolution. However, depending on the parameter of interest and the desired accuracy, higher resolutions are required, which will lead to an increase of computational times that still look very attractive towards clinical usability. The study shows that the next step towards an applicable individualized therapy for patients harboring intracranial aneurysms can be done. However, further in vivo validations are required to guarantee realistic predictions in future studies.
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http://dx.doi.org/10.1109/EMBC.2016.7591434DOI Listing
August 2016

Combined Visualization of Vessel Deformation and Hemodynamics in Cerebral Aneurysms.

IEEE Trans Vis Comput Graph 2017 01;23(1):761-770

We present the first visualization tool that combines patient-specific hemodynamics with information about the vessel wall deformation and wall thickness in cerebral aneurysms. Such aneurysms bear the risk of rupture, whereas their treatment also carries considerable risks for the patient. For the patient-specific rupture risk evaluation and treatment analysis, both morphological and hemodynamic data have to be investigated. Medical researchers emphasize the importance of analyzing correlations between wall properties such as the wall deformation and thickness, and hemodynamic attributes like the Wall Shear Stress and near-wall flow. Our method uses a linked 2.5D and 3D depiction of the aneurysm together with blood flow information that enables the simultaneous exploration of wall characteristics and hemodynamic attributes during the cardiac cycle. We thus offer medical researchers an effective visual exploration tool for aneurysm treatment risk assessment. The 2.5D view serves as an overview that comprises a projection of the vessel surface to a 2D map, providing an occlusion-free surface visualization combined with a glyph-based depiction of the local wall thickness. The 3D view represents the focus upon which the data exploration takes place. To support the time-dependent parameter exploration and expert collaboration, a camera path is calculated automatically, where the user can place landmarks for further exploration of the properties. We developed a GPU-based implementation of our visualizations with a flexible interactive data exploration mechanism. We designed our techniques in collaboration with domain experts, and provide details about the evaluation.
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http://dx.doi.org/10.1109/TVCG.2016.2598795DOI Listing
January 2017

The Computational Fluid Dynamics Rupture Challenge 2013--Phase II: Variability of Hemodynamic Simulations in Two Intracranial Aneurysms.

J Biomech Eng 2015 Dec;137(12):121008

With the increased availability of computational resources, the past decade has seen a rise in the use of computational fluid dynamics (CFD) for medical applications. There has been an increase in the application of CFD to attempt to predict the rupture of intracranial aneurysms, however, while many hemodynamic parameters can be obtained from these computations, to date, no consistent methodology for the prediction of the rupture has been identified. One particular challenge to CFD is that many factors contribute to its accuracy; the mesh resolution and spatial/temporal discretization can alone contribute to a variation in accuracy. This failure to identify the importance of these factors and identify a methodology for the prediction of ruptures has limited the acceptance of CFD among physicians for rupture prediction. The International CFD Rupture Challenge 2013 seeks to comment on the sensitivity of these various CFD assumptions to predict the rupture by undertaking a comparison of the rupture and blood-flow predictions from a wide range of independent participants utilizing a range of CFD approaches. Twenty-six groups from 15 countries took part in the challenge. Participants were provided with surface models of two intracranial aneurysms and asked to carry out the corresponding hemodynamics simulations, free to choose their own mesh, solver, and temporal discretization. They were requested to submit velocity and pressure predictions along the centerline and on specified planes. The first phase of the challenge, described in a separate paper, was aimed at predicting which of the two aneurysms had previously ruptured and where the rupture site was located. The second phase, described in this paper, aims to assess the variability of the solutions and the sensitivity to the modeling assumptions. Participants were free to choose boundary conditions in the first phase, whereas they were prescribed in the second phase but all other CFD modeling parameters were not prescribed. In order to compare the computational results of one representative group with experimental results, steady-flow measurements using particle image velocimetry (PIV) were carried out in a silicone model of one of the provided aneurysms. Approximately 80% of the participating groups generated similar results. Both velocity and pressure computations were in good agreement with each other for cycle-averaged and peak-systolic predictions. Most apparent "outliers" (results that stand out of the collective) were observed to have underestimated velocity levels compared to the majority of solutions, but nevertheless identified comparable flow structures. In only two cases, the results deviate by over 35% from the mean solution of all the participants. Results of steady CFD simulations of the representative group and PIV experiments were in good agreement. The study demonstrated that while a range of numerical schemes, mesh resolution, and solvers was used, similar flow predictions were observed in the majority of cases. To further validate the computational results, it is suggested that time-dependent measurements should be conducted in the future. However, it is recognized that this study does not include the biological aspects of the aneurysm, which needs to be considered to be able to more precisely identify the specific rupture risk of an intracranial aneurysm.
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http://dx.doi.org/10.1115/1.4031794DOI Listing
December 2015

An automatic CFD-based flow diverter optimization principle for patient-specific intracranial aneurysms.

J Biomech 2015 Nov 3;48(14):3846-52. Epub 2015 Oct 3.

Institute for Neuroradiology, University of Magdeburg "Otto von Guericke", Germany.

The optimal treatment of intracranial aneurysms using flow diverting devices is a fundamental issue for neuroradiologists as well as neurosurgeons. Due to highly irregular manifold aneurysm shapes and locations, the choice of the stent and the patient-specific deployment strategy can be a very difficult decision. To support the therapy planning, a new method is introduced that combines a three-dimensional CFD-based optimization with a realistic deployment of a virtual flow diverting stent for a given aneurysm. To demonstrate the feasibility of this method, it was applied to a patient-specific intracranial giant aneurysm that was successfully treated using a commercial flow diverter. Eight treatment scenarios with different local compressions were considered in a fully automated simulation loop. The impact on the corresponding blood flow behavior was evaluated qualitatively as well as quantitatively, and the optimal configuration for this specific case was identified. The virtual deployment of an uncompressed flow diverter reduced the inflow into the aneurysm by 24.4% compared to the untreated case. Depending on the positioning of the local stent compression below the ostium, blood flow reduction could vary between 27.3% and 33.4%. Therefore, a broad range of potential treatment outcomes was identified, illustrating the variability of a given flow diverter deployment in general. This method represents a proof of concept to automatically identify the optimal treatment for a patient in a virtual study under certain assumptions. Hence, it contributes to the improvement of virtual stenting for intracranial aneurysms and can support physicians during therapy planning in the future.
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http://dx.doi.org/10.1016/j.jbiomech.2015.09.039DOI Listing
November 2015