Biomedical subjects

Baoshun Ma

Publications and source records attributed to Baoshun Ma.

5 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

An anatomically based hybrid computational model of the human lung and its application to low frequency oscillatory mechanics.

Lung input impedance measured via forced oscillation over low frequency range has been confirmed as sensitive to the degree and the heterogeneity of lung disease. In this study we advanced an image-based, multi-scale computational model for the human lung, which includes upper and central airways, small airways and alveoli tissue unit. A three-dimensional (3-D) realistic model of the upper airway (reconstructed from MRI images) was combined with an anatomically based 3-D model of the central airways (based on MDCT images) to form a 3-D model of the large airways (from mouth to generation 6, incomplete for generations 4-6). The small airway trees distal to the central branches were based on a hypothetical airway tree for a normal healthy lung. A constant phase viscoelastic model was assumed for the alveolar tissue unit. Unsteady airflows in the large airways were simulated based on computational fluid dynamics (CFD). An experimentally measured broadband forcing flow was applied at the mouth. The impedance of the small airways was computed based on a one-dimensional transmission line model. The computed overall dynamic lung resistance and elastance compared very well with experimental values. Results showed that unsteady 3-D simulation and realistic geometry of the upper and large airways up to generations 4-6 can provide a reasonably accurate estimation of lung input impedance. The impedance of the upper airway constitutes a significant part of the total lung input impedance. The resistance of the upper airway accounts for 45-70% of the total lung resistance at frequencies between 0 and 1 Hz, and 70-81% at frequencies between 1 and 8 Hz.

Biological Clocks↗

PubMed2006

Non-invasive determination of zero-pressure geometry of arterial aneurysms.

Arterial aneurysms are in a pre-deformed state in vivo under non-zero pressure. The ability to determine their zero pressure geometry may help in improving accuracy of determination of stress distribution and reverse estimation of material properties from dynamic imaging data. An approximate method to recover the zero pressure geometry of the AAA is proposed. This method is motivated by the observation that the patterns in displacement field for a given AAA are strikingly consistent in an AAA under all physiological pressures. The basic principle is to leverage this observation to iteratively identify the geometry that when subjected to the in vivo pressure, will recover the geometry reconstructed from in vivo imaging. The methodology is demonstrated and validated using patient-specific AAA models.

Aortic Aneurysm, Abdominal↗

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↗