Seong Wook Cho

Construction of healthy arteries using computed tomography and virtual histology intravascular ultrasound

Vessel geometry for numerical analysis is generally obtained by computed tomography (CT) or magnetic resonance imaging (MRI) and intravascular ultrasound (IVUS). Most medical imaging is obtained from patients for hemodynamic analysis due to the properties of vascular disease and the difficulties in angiography. To predict the site where plaque occurs and understand the progression of the lesion, however, it is necessary to take into consideration not only the diseased artery, but also the blood flow characteristics of healthy artery. In order to simulate healthy vessels prior to lesion formation, we performed CT and virtual histology intravascular ultrasound (VH-IVUS) on three actual patients and this data was used to develop criteria for healthy vessel construction, a method that virtually removes all intravascular plaque. The lumen of a vessel generated by CT and the lumen from VH-IVUS were compared, and the cross-sectional areas of plaque components (fibrous, fibrofatty, dense calcium, and necrotic) and the lumen from VH-IVUS were analyzed. Geometric differences in the healthy vessel and diseased vessel were analyzed, and flow characteristics of the healthy vessel and diseased vessel were compared through computational fluid dynamics simulation. Low average wall shear stress (AWSS) was distributed in the site where plaque was removed from the healthy vessel, and a high oscillatory shear index (OSI) was observed in the region proximal to the site where plaque previously existed. Low AWSS and high OSI are widely accepted indicators of plaque formation or the direction of plaque progression. A numerical model that effectively predicts lesion forming sites was also generated based on the healthy vessel construction method presented in this study.

Numerical Study on Blood Flow Characteristics of the Stenosed Blood Vessel with Periodic Acceleration and Rotating Effect

The present study is carried out in order to investigate the effect of a periodic acceleration and rotating effects in a stenosed blood vessel. The blood flow and wall shear stress are changed under body movement or acceleration variation. Numerical studies are performed for various periodic acceleration phase angle and axial rotation speed. It is found that blood flow and wall shear stress are changed as variation of acceleration phase angle with the same periodic frequency also wall shear stress and blood flow rate are increased rapidly as increasing rotation speed.

Finite element modeling for predicting the contact pressure between a foam mattress and the human body in a supine position

Abstract In this paper, we generated finite element (FE) models to predict the contact pressure between a foam mattress and the human body in a supine position. Twenty-year-old males were used for three-dimensional scanning to produce the FE human models, which was composed of skin and muscle tissue. A linear elastic isotropic material model was used for the skin, and the Mooney–Rivlin model was used for the muscle tissue because it can effectively represent the nonlinear behavior of muscle. The contact pressure between the human model and the mattress was predicted by numerical simulation. The human models were validated by comparing the body pressure distribution obtained from the same human subject when he was lying on two different mattress types. The experimental results showed that the slope of the lower part of the mattress caused a decrease in the contact pressure at the heels, and the effect of bone structure was most pronounced in the scapula. After inserting a simple structure to function as the scapula, the contact pressure predicted by the FE human models was consistent with the experimental body pressure distribution for all body parts. These results suggest that the models proposed in this paper will be useful to researchers and designers of products related to the prevention of pressure ulcers.

Study of Blood Characteristics in Stenosed Artery under Human Body Rotation by Using FSI Method

In this study, we performed a numerical analysis to investigate the effect of rotation on the blood flow and arterial wall behavior by using the FSI (fluid-structure interaction) technique. The geometry of the artery included 50% stenosis at the center. To simulate the rotational effect, 2-6 rps of axial velocity was applied to the arterial model. A spiral wave and asymmetric flow occurred due to the stenosis and axial rotation both in the rigid body model and in the FSI model. However, the arterial wall motion caused periodic and transient blood flow changes in the FSI model. The FRZ (fluid recirculation zone) decreased in the FSI model, which is a known predictor for the formation and vulnerability of plaque. Therefore, it is observed that arterial wall motion also influences the generation of the FRZ.

Tolerance Analysis Considering Weld Distortion by Use of Pregenerated Database

A general and efficient methodology has been developed to analyze dimensional variations of an assembly, taking into account of the weld distortion. Weld distortion is generally probabilistic because of the random nature of welding parameters such as the welding speed, maximum welding temperature, ambient temperature, etc. The methodology is illustrated by a very simple example of two perpendicular plates fillet-welded to each other. Two steps comprise the methodology: establishment of a weld-distortion database, and tolerance analysis using the database. To establish the database, thermo-elasto-plastic finite element analyses are conducted to compute the weld distortion for all combinations of discrete values of major welding parameters. In the second step of tolerance analysis, the weld distortion retrieved from the database is used in addition to the dimensional tolerances of the parts. As a result of such an analysis, sensitivities of the assembly’s dimensional variations to the part tolerances and weld distortion are obtained, which can be help improve the dimensional quality of the assembly.Copyright