Tomer Anor

Modeling Blood Flow Circulation in Intracranial Arterial Networks: A Comparative 3D/1D Simulation Study

We compare results from numerical simulations of pulsatile blood flow in two patient-specific intracranial arterial networks using one-dimensional (1D) and three-dimensional (3D) models. Specifically, we focus on the pressure and flowrate distribution at different segments of the network computed by the two models. Results obtained with 1D and 3D models with rigid walls show good agreement in massflow distribution at tens of arterial junctions and also in pressure drop along the arteries. The 3D simulations with the rigid walls predict higher amplitude of the flowrate and pressure temporal oscillations than the 1D simulations with compliant walls at various segments even for small time-variations in the arterial cross-sectional areas. Sensitivity of the flow and pressure with respect to variation in the elasticity parameters is investigated with the 1D model.

Large-scale simulation of the human arterial tree.

1 Full‐scale simulations of the virtual physiological human (VPH) will require significant advances in modelling, multiscale mathematics, scientific computing and further advances in medical imaging. Herein, we review some of the main issues that need to be resolved in order to make three‐dimensional (3D) simulations of blood flow in the human arterial tree feasible in the near future. 2 A straightforward approach is computationally prohibitive even on the emerging petaflop supercomputers, so a three‐level hierarchical approach based on vessel size is required, consisting of: (i) a macrovascular network (MaN); (ii) a mesovascular network (MeN); and (iii) a microvascular network (MiN). We present recent simulations of MaN obtained by solving the 3D Navier–Stokes equations on arterial networks with tens of arteries and bifurcations and accounting for the neglected dynamics through proper boundary conditions. 3 A multiscale simulation coupling MaN–MeN–MiN and running on hundreds of thousands of processors on petaflop computers will require no more than a few CPU hours per cardiac cycle within the next 5 years. The rapidly growing capacity of supercomputing centres opens up the possibility of simulation studies of cardiovascular diseases, drug delivery, perfusion in the brain and other pathologies.

Algorithms for design of continuum robots using the concentric tubes approach: A neurosurgical example

We propose a novel systematic approach to optimizing the design of concentric tube robots for neurosurgical procedures. These procedures require that the robot approach specified target sites while navigating and operating within an anatomically constrained work space. The availability of preoperative imaging makes our approach particularly suited for neurosurgery, and we illustrate the method with the example of endoscopic choroid plexus ablation. A novel parameterization of the robot characteristics is used in conjunction with a global pattern search optimization method. The formulation returns the design of the least-complex robot capable of reaching single or multiple target points in a confined space with constrained optimization metrics. A particular advantage of this approach is that it identifies the need for either fixed-curvature versus variable-curvature sections. We demonstrate the performance of the method in four clinically relevant examples.

Robotic neuro-emdoscope with concentric tube augmentation

Surgical robots are gaining favor in part due to their capacity to reach remote locations within the body. Continuum robots are especially well suited for accessing deep spaces such as cerebral ventricles within the brain. Due to the entry point constraints and complicated structure, current techniques do not allow surgeons to access the full volume of the ventricles. The ability to access the ventricles with a dexterous robot would have significant clinical implications. This paper presents a concentric tube manipulator mated to a robotically controlled flexible endoscope. The device adds three degrees of freedom to the standard neuroendoscope and roboticizes the entire package allowing the operator to conveniently manipulate the device. To demonstrate the improved functionality, we use an in-silica virtual model as well as an ex-vivo anatomic model of a patient with a treatable form of hydrocephalus. In these experiments we demonstrate that the augmented and roboticized endoscope can efficiently reach critical regions that a manual scope cannot.

Simulation of the human intracranial arterial tree

High-resolution unsteady three-dimensional flow simulations in large intracranial arterial networks of a healthy subject and a patient with hydrocephalus have been performed. The large size of the computational domains requires the use of thousands of computer processors and solution of the flow equations with approximately one billion degrees of freedom. We have developed and implemented a two-level domain decomposition method, and a new type of outflow boundary condition to control flow rates at tens of terminal vessels of the arterial network. In this paper, we demonstrate the flow patterns in the normal and abnormal intracranial arterial networks using patient-specific data.

Modeling of blood flow in arterial trees.

Advances in computational methods and medical imaging techniques have enabled accurate simulations of subject‐specific blood flows at the level of individual blood cell and in complex arterial networks. While in the past, we were limited to simulations with one arterial bifurcation, the current state‐of‐the‐art is simulations of arterial networks consisting of hundreds of arteries. In this paper, we review the advances in methods for vascular flow simulations in large arterial trees. We discuss alternative approaches and validity of various assumptions often made to simplify the modeling. To highlight the similarities and discrepancies of data computed with different models, computationally intensive three‐dimensional (3D) and inexpensive one‐dimensional (1D) flow simulations in very large arterial networks are employed. Finally, we discuss the possibilities, challenges, and limitations of the computational methods for predicting outcomes of therapeutic interventions for individual patients. Copyright

Evaluation of the ShuntCheck noninvasive thermal technique for shunt flow detection in hydrocephalic patients.

BACKGROUND:ShuntCheck (Neuro Diagnostic Devices, Inc., Trevose, Pennsylvania) is a new device designed to detect cerebrospinal fluid (CSF) flow in a shunt by sensing skin temperature downstream from a region of CSF cooled by an ice cube. OBJECTIVE:To understand its accuracy and utility, we evaluated the use of this device during routine office visits as well as during workup for suspected shunt malfunction. METHODS:One hundred shunted patients were tested, including 48 evaluated during possible shunt malfunction, of whom 24 went on to surgical exploration. Digitally recorded data were blindly analyzed and compared with surgical findings and clinical follow-up. RESULTS:Findings in the 20 malfunctioning shunts with unambiguous flow or absence of flow at surgery were strongly correlated with ShuntCheck results (sensitivity and specificity to flow of 80% and 100%, respectively, P = .0007, Fishers exact test, measure of agreement κ = 0.8). However, the thermal determination did not distinguish patients in the suspected malfunction group who received surgery from those who were discharged without surgery (P = .248 by Fishers exact test, κ = 0.20). Half of the patients seen in routine office visits did not have detectable flow, although none required shunt revision on clinical grounds. Intermittent flow was specifically demonstrated in one subject who had multiple flow determinations. CONCLUSION:Operative findings show that the technique is sensitive and specific for detecting flow, but failure to detect flow does not statistically predict the need for surgery. A better understanding of the normal dynamics of flow in individual patients, which this device may yield, will be necessary before the true clinical utility of non-invasive flow measurement can be assessed.

Transtentorial transcollateral sulcus approach to the ventricular atrium: an endoscope-assisted anatomical study

OBJECTIVE Conventional approaches to the atrium of the lateral ventricle may be associated with complications related to direct cortical injury or brain retraction. The authors describe a novel approach to the atrium through a retrosigmoid transtentorial transcollateral sulcus corridor. METHODS Bilateral retrosigmoid craniotomies were performed on 4 formalin-fixed, colored latex-injected human cadaver heads (a total of 8 approaches). Microsurgical dissections were performed under 3× to 24× magnification, and endoscopic visualization was provided by 0° and 30° rigid endoscope lens systems. Image guidance was provided by coupling an electromagnetic tracking system with an open source software platform. Objective measurements on cortical thickness traversed and total depth of exposure were recorded. Additionally, the basal occipitotemporal surfaces of 10 separate cerebral hemisphere specimens were examined to define the surface topography of sulci and gyri, with attention to the appearance and anatomical patterns and variations of the collateral sulcus and the surrounding gyri. RESULTS The retrosigmoid approach allowed for clear visualization of the basal occipitotemporal surface. The collateral sulcus was identified and permitted easy endoscopic access to the ventricular atrium. The conical corridor thus obtained provided an average base working area of 3.9 cm2 at an average depth of 4.5 cm. The mean cortical thickness traversed to enter the ventricle was 1.4 cm. The intraventricular anatomy of the ipsilateral ventricle was defined clearly in all 8 exposures in this manner. The anatomy of the basal occipitotemporal surface, observed in a total of 18 hemispheres, showed a consistent pattern, with the collateral sulcus abutted by the parahippocampal gyrus medially, and the fusiform and lingual gyrus laterally. The collateral sulcus was found to be caudally bifurcated in 14 of the 18 specimens. CONCLUSIONS The retrosigmoid supracerebellar transtentorial transcollateral sulcus approach is technically feasible. This approach has the potential advantage of providing a short and direct path to the atrium, hence avoiding violation of deep neurovascular structures and preserving eloquent areas. Although this approach appears unconventional, it may provide a minimally invasive option for the surgical management of selected lesions within the atrium of the lateral ventricle.

Large-scale simulation of the human cranial arterial tree: utility in hydrocephalus

Background Recent work in hydrocephalus modelling has drawn attention to the potential role of disruption of a pulsation absorber mechanism in the intracranial compartment. Therefore, characterization of cerebral hemodynamics is essential for understanding complex intracranial dynamics under normal and diseased conditions, diagnosing and treating patients suffering from hydrocephalus, and designing medical devices. To this end, we have developed a procedure for generating physiologically accurate models of the cerebral hemodynamics by coupling clinical data and the multiscale modelling approach.

Noninvasive Thermal Evaluation of Ventriculoperitoneal Shunt Patency and Cerebrospinal Fluid Flow Using a Flow Enhancing Device

BACKGROUND While a noninvasive flow determination would be desirable in the diagnosis of cerebrospinal fluid shunt malfunction, existing studies have not yet defined a role for thermal flow detection. OBJECTIVE To evaluate a revised test protocol using a micropumper designed to transiently enhance flow during thermal testing to determine whether thermal detection of flow is associated with progression to shunt revision surgery. METHODS Eighty-two unique tests were performed in 71 shunts. The primary outcome, need for revision within 7 d of testing, was compared with results of micropumper-augmented thermal flow detection. Statistical analysis was based on blind interpretation of test results and raw temperature data recorded during testing. RESULTS The test was sensitive (73%) and specific (68%) in predicting need for revision, with 5.6-fold higher probability of revision when flow was not detected. Negative predictive value in our sample was 94.2%. The probability of not requiring revision increased with increasing total temperature drop. Analysis of various possible thresholds showed that the optimal temperature cutoff may be lower than suggested by the manufacturer (0.125°C vs 0.2°C). CONCLUSION This is the first study to report a strong association between thermal flow evaluation and a clinical impression that a shunt is not malfunctioning. The current recommended threshold may increase the false positive rate unnecessarily, and as clinicians gain experience with the method, they may find value in examining the temperature curves themselves. Multicenter studies are suggested to further define a role for this diagnostic test.