The Influence of Dome Size, Parent Vessel Angle, and Coil Packing Density On Coil Embolization Treatment in Cerebral Aneurysms

abstract: A cerebral aneurysm is a bulging of a blood vessel in the brain. Aneurysmal rupture affects 25,000 people each year and is associated with a 45% mortality rate. Therefore, it is critically important to treat cerebral aneurysms effectively before they rupture. Endovascular coiling is the most effective treatment for cerebral aneurysms. During coiling process, series of metallic coils are deployed into the aneurysmal sack with the intent of reaching a sufficient packing density (PD). Coils packing can facilitate thrombus formation and help seal off the aneurysm from circulation over time. While coiling is effective, high rates of treatment failure have been associated with basilar tip aneurysms (BTAs). Treatment failure may be related to geometrical features of the aneurysm. The purpose of this study was to investigate the influence of dome size, parent vessel (PV) angle, and PD on post-treatment aneurysmal hemodynamics using both computational fluid dynamics (CFD) and particle image velocimetry (PIV). Flows in four idealized BTA models with a combination of dome sizes and two different PV angles were simulated using CFD and then validated against PIV data. Percent reductions in post-treatment aneurysmal velocity and cross-neck (CN) flow as well as percent coverage of low wall shear stress (WSS) area were analyzed. In all models, aneurysmal velocity and CN flow decreased after coiling, while low WSS area increased. However, with increasing PD, further reductions were observed in aneurysmal velocity and CN flow, but minimal changes were observed in low WSS area. Overall, coil PD had the greatest impact while dome size has greater impact than PV angle on aneurysmal hemodynamics. These findings lead to a conclusion that combinations of treatment goals and geometric factor may play key roles in coil embolization treatment outcomes, and support that different treatment timing may be a critical factor in treatment optimization.Dissertation/ThesisM.S. Bioengineering 201

A Comprehensive Numerical Approach to Coil Placement in Cerebral Aneurysms: Mathematical Modeling and In Silico Occlusion Classification

Endovascular coil embolization is one of the primary treatment techniques for cerebral aneurysms. Although it is a well established and minimally invasive method, it bears the risk of sub-optimal coil placement which can lead to incomplete occlusion of the aneurysm possibly causing recurrence. One of the key features of coils is that they have an imprinted natural shape supporting the fixation within the aneurysm. For the spatial discretization our mathematical coil model is based on the Discrete Elastic Rod model which results in a dimension-reduced 1D system of differential equations. We include bending and twisting responses to account for the coils natural curvature. Collisions between coil segments and the aneurysm-wall are handled by an efficient contact algorithm that relies on an octree based collision detection. The numerical solution of the model is obtained by a symplectic semi-implicit Euler time stepping method. Our model can be easily incorporated into blood flow simulations of embolized aneurysms. In order to differentiate optimal from sub-optimal placements, we employ a suitable in silico Raymond-Roy type occlusion classification and measure the local packing density in the aneurysm at its neck, wall-region and core. We investigate the impact of uncertainties in the coil parameters and embolization procedure. To this end, we vary the position and the angle of insertion of the microcatheter, and approximate the local packing density distributions by evaluating sample statistics

Aneurysmal Subarachnoid Hemorrhage : Posterior Communicating Artery Aneurysms and Long-Term Excess Mortality

Introduction Aneurysmal subarachnoid hemorrhage (aSAH) is a serious form of stroke, caused by a ruptured intracranial aneurysm. The origin of the posterior communicating artery (PComA) is one of the most common locations for ruptured aneurysms causing aSAH. There are specific features related to the rupture and occlusive treatment of PComA aneurysms. It has been believed that after successful rehabilitation aSAH patients should have a similar life-expectancy to that of the general population. However, lately there have been indications of excess mortality in the long run. The aims of this work are 1) to identify the morphological features related to PComA aneurysms and their rupture, 2) to study the treatment and outcome after PComA aneurysm rupture and aSAH, 3) to discover if there is long-term excess mortality after aSAH compared to the general population. Patients and Methods Each publication includes a subgroup of 7289 patients with intracranial aneurysms treated in Helsinki University Hospital between 1980 and 2014. The computed tomography angiography analysis on PComA aneurysm morphology was based on images of 391 patients; the treatment and outcome was evaluated in 620 patients with ruptured PComA aneurysm and long-term excess mortality was evaluated after follow-up of 3078 aSAH survivors. Results The most marked morphological features of the PComA aneurysms were saccularity (99%), inferoposterior dome orientation (42%), infrequency of large or giant aneurysms (4%), narrow neck compared to the aneurysm size, PComA originating directly from the aneurysm neck or the dome (28%), and fetal or dominant PComA on the side of the aneurysm (35%). A notable proportion (38%) of PComA aneurysms ruptured at small sizes (<7mm), and there were location-related parameters like irregular aneurysm dome that were associated with rupture. Most of the patients made a good recovery at 1 year after PComA aneurysm rupture and aSAH (62%). A small proportion of patients were left severely disabled (4%), and 20% died during the first year. The risk factors for impaired outcome were poor preoperative clinical condition, intracerebral or subdural hematoma due to aneurysm rupture, age over 65, artery occlusion in postoperative angiography, occlusive treatment-related ischemia, delayed cerebral vasospasm and hydrocephalus requiring a shunt. There was long-term excess mortality after aSAH compared to matched general population even among young patients and patients who recovered well initially. The highest excess mortality was among patients with multiple aneurysms, old age, poor preoperative clinical condition, conservative aneurysm treatment, and unfavorable clinical outcome at 1 year. Conclusions PComA aneurysms rupture also at small sizes, and there are location-related morphological parameters associated with the rupture. Even though most treated aSAH patients recover well after PComA aneurysm rupture, there are occlusive treatment-related complications like artery occlusions and treatment-related brain infarctions causing impaired outcome irrespective of the treatment method. PComA aneurysms may have been seen as uncomplicated lesions, but occlusive treatment of a ruptured PComA aneurysm seems to be a high-risk procedure. There is excess mortality after aSAH among patients with all aneurysm locations in a long-term follow-up. Cardio- and cerebrovascular causes were overrepresented as causes of death. Treatment of vascular risk factors is important after aSAH. Certain patient groups require follow-up.Johdanto Lukinkalvonalainen verenvuoto (SAV) aivovaltimopullistumasta eli aneurysmasta on vakava aivoverenkiertohäiriö. Takimmaisen yhdysvaltimon haarautumiskohta on yksi yleisimmistä sijainneista vuodon aiheuttaneelle aneurysmalle. Näiden hoitoon liittyy juuri tälle sijainnille tyypillisiä haasteita. Aiemmin on ajateltu, että onnistuneen kuntoutumisen jälkeen SAV-potilaiden elinajanodote on vastaava kuin normaaliväestöllä. Viimeaikaiset tutkimustulokset ovat kuitenkin antaneet viitteitä siitä, että SAV:sta toipuneilla saattaa olla ylikuolleisuutta suhteessa normaaliväestöön. Tutkimuksemme tavoitteita ovat: 1) tutkia morfologisia piirteitä, jotka liittyvät takimmaisen yhdysvaltimon aneurysmiin sekä niiden puhkeamiseen, 2) raportoida hoidon tulokset sekä mahdolliset toipumista heikentävät seikat takimmaisen yhdysvaltimon aneurysman puhkeamisesta seuranneen SAV:n jälkeen sekä 3) ottaa selvää, esiintyykö SAV :n jälkeen ylikuolleisuutta. Metodit Jokainen julkaisu sisältää alaryhmän 7289 potilaasta, jotka on hoidettu vuotaneen tai vuotamattoman aneurysman vuoksi Helsingin seudun yliopistollisessa keskussairaalassa vuosina 1980-2014. Tietokonetomografiakuva-analyysi perustui 391 potilaan kuviin; hoidon ja toipumisen suhteen arvioitiin 620 potilasta, jotka oli hoidettu takimmaisen yhdysvaltimon aneurysman puhkeamisesta seuranneen SAV:n vuoksi; ja ylikuolleisuutta arvioitiin 3078 SAV:sta selviytyneen potilaan pitkäaikaisseurannassa. Tulokset Määritimme takimmaisen yhdysvaltimon aneurysman tyyppipiirteet. Havaitsimme, että kliinisesti merkittävä paksu kehityksellinen jäänne takimmaisesta yhdysvaltimosta aneurysmaan liittyen oli tavallinen (35%). Vaikka aneurysman koon lisääntyminen yleisesti suurentaa vuororiskiä, havaitsimme, että takimmaisen yhdysvaltimon aneurysmat vuotivat usein myös pienikokoisina. Suurin osa potilaista, jotka olivat sairastaneet SAV:n takimmaisen yhdysvaltimon aneurysmasta, toipuivat hyvin vuoden kuluessa (62%). Vain pieni osa potilaista jäi vaikeasti vammautuneeksi (4%), ja joka viides menehtyi ensimmäisen vuoden kuluessa. Riskitekijöitä heikommalle toipumiselle olivat huono leikkausta edeltävä kunto, aivokudoksensisäinen tai kovakalvonalainen verenvuoto SAV:oon liittyen, yli 65 vuoden ikä, aivovaltimon tukkeuma kontrollikuvaksessa, aneurysman hoitoon liittyvä aivoverenkiertohäiriö, viiveellä ilmenevä oireinen aivovaltimoiden spasmi tai vuodon jälkeinen vesipäisyys, joka vaati aivokammiosuntin. Totesimme SAV:n sairastaneilla ylikuolleisuutta pitkässä seurannassa suhteessa normaaliväestöön. Ylikuolleisuus korostui potilailla, joilla oli useita aneurysmia, iäkkäillä, ennen hoitoa huonokuntoisilla sekä niillä, joiden toipuminen oli heikkoa vuoden kohdalla sairastumisesta. Johtopäätökset Takimmaisen yhdysvaltimon aneurysmat vuotavat usein pieninäkin, ja havaitsimme koon lisäksi muita piirteitä, jotka liittyivät puhkeamiseen. Vaikka suurin osa hoidetuista potilaista toipuu varsin hyvin takimmaisen yhdysvaltimon aneurysmavuodon jälkeen, aneurysman hoitoon liittyy haasteita, kuten aivovaltimon tukkeumia sekä aivoinfarkteja, jotka heikentävät toipumista. Näitä esiintyi kaikissa hoitomuodossa. Takimmaisen yhdysvaltimon aneurysmien hoito on nähty melko mutkattomana, mutta se vaikuttaa riskialttiilta toimenpiteeltä. SAV:sta toipuneilla potilailla esiintyy ylikuolleisuutta suhteessa normaaliväestöön pitkäaikaisseurannassa. Sydän- ja aivoverisuonisairaudet korostuivat kuolinsyinä. Verisuonisairauksien riskitekijöiden hoito on hyvin tärkeää SAV:n jälkeen.Tietyt potilaat vaativat tehostettua seurantaa

A (Near) Real-Time Simulation Method of Aneurysm Coil Embolization

International audienceA (Near) Real-Time Simulation Method of Aneurysm Coil Embolizatio

Guest Editorial Special Issue on Medical Imaging and Image Computing in Computational Physiology

International audienceThe January 2013 Special Issue of IEEE transactions on medical imaging discusses papers on medical imaging and image computing in computational physiology. Aslanid and co-researchers present an experimental technique based on stained micro computed tomography (CT) images to construct very detailed atrial models of the canine heart. The paper by Sebastian proposes a model of the cardiac conduction system (CCS) based on structural information derived from stained calf tissue. Ho, Mithraratne and Hunter present a numerical simulation of detailed cerebral venous flow. The third category of papers deals with computational methods for simulating medical imagery and incorporate knowledge of imaging physics and physiology/biophysics. The work by Morales showed how the combination of device modeling and virtual deployment, in addition to patient-specific image-based anatomical modeling, can help to carry out patient-specific treatment plans and assess alternative therapeutic strategies

Neurovascular Surgery

This open access book presents the diagnosis, investigation and treatment of neurovascular diseases, and offers expert opinions and advice on avoiding complications in neurovascular surgery. It also covers complication management and post-operative follow-up care. The book is divided in to three parts; the first part discusses common approaches in neurovascular surgery, describing the steps, indications for and limitations of the approach, as well as the associated complications and how to avoid them. The second part addresses surgical treatment based on pathology, taking the different locations of lesions into consideration. The third part focuses on the technological developments that support neurovascular surgery, which may not be available everywhere, but have been included to help vascular surgeon understand the principles. This book is a guide for young neurosurgeons, neurosurgery residents and neurosurgery fellows, as well as for medical students and nurses who are interested in neurosurgery or are associated with this field in any way. It is also a useful teaching aid for senior neurosurgeons

Neurovascular Surgery

This open access book presents the diagnosis, investigation and treatment of neurovascular diseases, and offers expert opinions and advice on avoiding complications in neurovascular surgery. It also covers complication management and post-operative follow-up care. The book is divided in to three parts; the first part discusses common approaches in neurovascular surgery, describing the steps, indications for and limitations of the approach, as well as the associated complications and how to avoid them. The second part addresses surgical treatment based on pathology, taking the different locations of lesions into consideration. The third part focuses on the technological developments that support neurovascular surgery, which may not be available everywhere, but have been included to help vascular surgeon understand the principles. This book is a guide for young neurosurgeons, neurosurgery residents and neurosurgery fellows, as well as for medical students and nurses who are interested in neurosurgery or are associated with this field in any way. It is also a useful teaching aid for senior neurosurgeons

Efficient ensemble simulation methods for in-silico trials of endovascular medical devices

In-silico trials (ISTs) use computational modelling and simulation in virtual patients to evaluate medical device performance. Despite early promise, various challenges prevent the use of ISTs from becoming common practice in medical device development. Three significant challenges are: (i) Prohibitive costs due to complex computational models that require excessive resources and time to execute. (ii) Lack of exemplar ISTs demonstrating their effectiveness in generating evidence for medical device performance. (iii) Lack of scalability and reproducibility due to computational modelling pipelines requiring significant expert manual input. In this thesis, challenge (i) was addressed through a comprehensive literature review into reduced order modelling and machine learning techniques that can accelerate the computational models that are essential in ISTs. Challenge (ii) was addressed by performing the FD-PComA IST into flow diversion (FD) of posterior communicating artery (PComA) aneurysms, which are a common sub-group currently not approved for treatment with the most widely used flow diverter. PComA aneurysm treatment is complicated by the presence of fetal posterior circulation (FPC), which has an estimated prevalence of 4-29% and is more common in black than white ethnicities. Given these factors, FD-PComA demonstrates the effectiveness of ISTs in generating evidence for less-studied scenarios and demographics. Challenge (iii) was addressed in FD-PComA through automation of the modelling steps. The results of FD-PComA demonstrate that flow diversion is less effective in FPC patients and that PComA and aneurysm morphology do not influence treatment performance. Challenge (i) was addressed further through the development of a machine learning reduced order model (ML-ROM) for evaluating aneurysm blood flow subject to physiological variation, which is a relevant problem for IST applications. The ML-ROM was approximately 98% accurate in evaluating the velocity solution and provided an acceleration of five orders of magnitude relative to a computational fluid dynamics model for the same problem

Improving Cardiovascular Stent Design Using Patient-Specific Models and Shape Optimization

Stent geometry influences local hemodynamic alterations (i.e. the forces moving blood through the cardiovascular system) associated with adverse clinical outcomes. Computational fluid dynamics (CFD) is frequently used to quantify stent-induced hemodynamic disturbances, but previous CFD studies have relied on simplified device or vascular representations. Additionally, efforts to minimize stent-induced hemodynamic disturbances using CFD models often only compare a small number of possible stent geometries. This thesis describes methods for modeling commercial stents in patient-specific vessels along with computational techniques for determining optimal stent geometries that address the limitations of previous studies. An efficient and robust method was developed for virtually implanting stent models into patient-specific vascular geometries derived from medical imaging data. Models of commercial stent designs were parameterized to allow easy control over design features. Stent models were then virtually implanted into vessel geometries using a series of Boolean operations. This approach allowed stented vessel models to be automatically regenerated for rapid analysis of the contribution of design features to resulting hemodynamic alterations. The applicability of the method was demonstrated with patient-specific models of a stented coronary artery bifurcation and basilar trunk aneurysm to reveal how it can be used to investigate differences in hemodynamic performance in complex vascular beds for a variety of clinical scenarios. To identify hemodynamically optimal stents designs, a computational framework was constructed to couple CFD with a derivative-free optimization algorithm. The optimization algorithm was fully-automated such that solid model construction, mesh generation, CFD simulation and time-averaged wall shear stress (TAWSS) quantification did not require user intervention. The method was applied to determine the optimal number of circumferentially repeating stent cells (NC) for a slotted-tube stents and various commercial stents. Optimal stent designs were defined as those minimizing the area of low TAWSS. It was determined the optimal value of NC is dependent on the intrastrut angle with respect to the primary flow direction. Additionally, the geometries of current commercial stents were found to generally incorporate a greater NC than is hemodynamically optimal. The application of the virtual stent implantation and optimization methods may lead to stents with superior hemodynamic performance and the potential for improved clinical outcomes. Future in vivo studies are needed to validate the findings of the computational results obtained from the methods developed in this thesis