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Biomedical subjects

Robert E Harbaugh

Publications and source records attributed to Robert E Harbaugh.

10 recordsLinked to original sources
PubMed2007

Nonlinear anisotropic stress analysis of anatomically realistic cerebral aneurysms.

BACKGROUND: Static deformation analysis and estimation of wall stress distribution of patient-specific cerebral aneurysms can provide useful insights into the disease process and rupture. METHOD OF APPROACH: The three-dimensional geometry of saccular cerebral aneurysms from 27 patients (18 unruptured and nine ruptured) was reconstructed based on computer tomography angiography images. The aneurysm wall tissue was modeled using a nonlinear, anisotropic, hyperelastic material model (Fung-type) which was incorporated in a user subroutine in ABAQUS. Effective material fiber orientations were assumed to align with principal surface curvatures. Static deformation of the aneurysm models were simulated assuming uniform wall thickness and internal pressure load of 100 mm Hg. RESULTS: The numerical analysis technique was validated by quantitative comparisons to results in the literature. For the patient-specific models, in-plane stresses in the aneurysm wall along both the stiff and weak fiber directions showed significant regional variations with the former being higher. The spatial maximum of stress ranged from as low as 0.30 MPa in a small aneurysm to as high as 1.06 MPa in a giant aneurysm. The patterns of distribution of stress, strain, and surface curvature were found to be similar. Sensitivity analyses showed that the computed stress is mesh independent and not very sensitive to reasonable perturbations in model parameters, and the curvature-based criteria for fiber orientations tend to minimize the total elastic strain energy in the aneurysms wall. Within this small study population, there were no statistically significant differences in the spatial means and maximums of stress and strain values between the ruptured and unruptured groups. However, the ratios between the stress components in the stiff and weak fiber directions were significantly higher in the ruptured group than those in the unruptured group. CONCLUSIONS: A methodology for nonlinear, anisotropic static deformation analysis of geometrically realistic aneurysms was developed, which can be used for a more accurate estimation of the stresses and strains than previous methods and to facilitate prospective studies on the role of stress in aneurysm rupture.

Anisotropy↗
PubMed2006

Training residents in endovascular neurosurgery.

Neurosurgeons have a long history of treating cerebrovascular disease. Understanding the vascular anatomy and physiology of the nervous system and management of patients with abnormalities of theses vascular structures are vitally important aspects of neurosurgery resident training. Over the past decade, the treatment of cerebrovascular disease has been evolving toward endovascular strategies for many patients. Interventional neuroradiologists were the pioneers in developing this area of therapy, but the number of neurosurgical trainees in neuroendovascular treatment is increasing, and other specialties, including neurology, vascular surgery, and cardiology, are now entering the field of neuroendovascular treatment. The purpose of this article is to review the current credentialing guidelines for neurosurgeons to use endovascular techniques in the treatment of cerebrovascular disease and to consider options for resident training in the rapidly evolving field of endovascular neurosurgery.

Credentialing↗
PubMed2005

Quantified aneurysm shape and rupture risk.

OBJECT: The authors investigated whether quantified shape or size indices could better discriminate between ruptured and unruptured aneurysms. METHODS: Several custom algorithms were created to quantifiy the size and shape indices of intracranial aneurysms by using three-dimensional computerized tomography angiography models of the brain vasculature. Data from 27 patients with ruptured or unruptured aneurysms were evaluated in a blinded fashion to determine whether aneurysm size or shape better discriminated between the ruptured and unruptured groups. Five size and eight shape indices were calculated for each aneurysm. Two-tailed independent Student t-tests (significance p < 0.05) were used to determine statistically significant differences between ruptured and unruptured aneurysm groups for all 13 indices. Receiver-operating characteristic-area under curve analyses were performed for all indices to quantify the predictability of each index and to identify optimal threshold values. None of the five size indices were significantly different between the ruptured and unruptured aneurysms. Five of the eight shape indices were significantly different between the two lesion groups, and two other shape indices showed a trend toward discriminating between ruptured and unruptured aneurysms, although these differences did not reach statistical significance. CONCLUSIONS: Quantified shape is more effective than size in discriminating between ruptured and unruptured aneurysms. Further investigation will determine whether quantified aneurysm shape will prove to be a reliable predictor of aneurysm rupture.

Adult↗
PubMed2004

Three-dimensional geometrical characterization of cerebral aneurysms.

The risk of rupture of cerebral aneurysms has been correlated with the size of the aneurysm sac. It is conceivable that geometrical shape, not just size may also be related to aneurysm rupture potential. Further, aneurysm shape may also be a factor in deciding on treatment modalities, i.e., to clip or coil. However, our ability to make use of available information on aneurysm shape remains poor. In this study, methods were developed to quantify the seemingly arbitrary three-dimensional geometry of the aneurysm sac, using differential and computational geometry techniques. From computed tomography angiography (CTA) data, the three-dimensional geometry of five unruptured human cerebral aneurysms was reconstructed. Various indices (maximum diameter, neck diameter, height, aspect ratio, bottleneck factor, bulge location, volume, surface area, Gaussian and mean curvatures, isoperimetric ratio, and convexity ratio) were utilized to characterize the geometry of these aneurysm surfaces and four size-matched hypothetical control aneurysms. The physical meanings of various indices and their possible role as prognosticators for rupture risk and presurgical planning were discussed.

Algorithms↗
PubMed2004

Methods and design considerations for randomized clinical trials evaluating surgical or endovascular treatments for cerebrovascular diseases.

OBJECTIVE: The results of clinical trials affect the practice of surgery and endovascular therapy for cerebrovascular diseases. The purpose of this report is to review the basic components of the designs and methods for randomized clinical trials and to describe the influence of those components on the interpretation of trial results. METHODS: The goal of an optimal clinical trial of a new procedure is to provide the most objective and rigorous evaluation of the safety and effectiveness of that procedure. Anything in the design, performance, or analysis that impairs such an assessment decreases the ability of the trial to achieve its goal and answer the research question. To highlight the components of a clinical trial, this report uses examples of Phase III clinical trials that have influenced the practice of cerebrovascular surgery and endovascular therapy in the past three decades, including the International Cooperative Study of Extracranial/Intracranial Arterial Anastomosis, the North American Symptomatic Carotid Endarterectomy Trial, the Asymptomatic Carotid Atherosclerosis Study, the Prolyse in Acute Cerebral Thromboembolism II study, and the International Subarachnoid Aneurysm Trial. RESULTS: The research question (objective) of the trial must be clearly defined, with an objective measure of efficacy and a specified quantitative difference to define the superiority of one intervention over another, in a relatively homogeneous patient population. Allocation concealment, randomization with or without stratification, and blinding (or masking) are important strategies to prevent differences in the study populations that could adversely affect the conclusions of the study. The primary end point must correspond to the specific aims of the trial. It should be objectively defined, quantifiable, reliable, and reproducible. Commonly defined end points in surgical trials include changes from baseline illness or disease severity scores, morbidity and mortality rates, and relative risks of reaching an end point with time. The statistical methods used for interim and final analyses are important. The effects of dropouts, crossovers, and missing data should be understood in the context of the final analysis. Additional concepts, such as intention-to-treat analysis and use of actual versus predicted outcomes, are important with respect to interpretation of the final results of the study. CONCLUSION: The neurosurgical and neuroendovascular communities are currently planning or conducting several clinical trials to evaluate new procedures for the treatment of cerebrovascular diseases. It is hoped that a better understanding of the components of clinical trials will facilitate the design and implementation of effective studies.

Angioplasty↗
PubMed2003

More on ISAT.

Explore the source record for details and available documents.

Aneurysm, Ruptured↗
PubMed2002

Carotid endarterectomy in high risk patients.

We elected to compare the clinical outcomes of carotid endarterectomy (CEA) patients who were thought to be at increased risk for peri-operative complications because of advanced age (> 79 years), medical comorbidities and contralateral internal carotid artery occlusion to patients without these risk factors. A prospective series of 875 CEAs done using regional anesthesia were analyzed. All patients were operated upon under the direction of one neurosurgeon (REH). Clinical outcomes measures evaluated were any stroke, death or myocardial infarction within 30 days of operation. All patients were followed to a clinical endpoint and/or six weeks post-operatively. The incidence of adverse clinical outcomes in the suspected high risk patients was compared to the incidence in the entire series using contingency table analysis (Chi-square and Fisher's exact test). Twenty strokes (2.3%), four myocardial infarctions (0.5%) and three deaths (0.3%) occurred within 30 days of CEA. None of the suspected risk factors was associated with a significantly (p < 0.05) increased risk of peri-operative morbidity or mortality. CEA using regional anesthesia can be performed in patients with advanced age, diabetes mellitus, atherosclerotic coronary vascular disease and contralateral ICA occlusion with acceptably low peri-operative morbidity.

Age Factors↗