Biomedical Image Processing / Medical Image Processing
Seyed Mohammad Shams; Gholam Ali Hossein-Zadeh; Mohammad Mehdi Karimi
Volume 1, Issue 1 , June 2007, , Pages 29-37
Abstract
In order to analyze the functional Magnetic Resonance Imaging (fMRI) data, the parameters of a nonlinear model for the hemodynamic system, so called Balloon model, were characterized and estimated. Two different approaches were applied to estimate these parameters. In the first step of both approaches, ...
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In order to analyze the functional Magnetic Resonance Imaging (fMRI) data, the parameters of a nonlinear model for the hemodynamic system, so called Balloon model, were characterized and estimated. Two different approaches were applied to estimate these parameters. In the first step of both approaches, the voxels which show neural activity were identified. Then, the parameters of the balloon model for these active voxels were estimated by both steepest descent algorithm, and through genetic algorithm. Proposed approaches were applied on experimental fMRI data and the parameters of nonlinear Balloon model were estimated for different brain voxels. Accuracy of these characterizations was assessed via comparing the measured time series at each voxel with the modeled time series. Also, it was shown that the results of the parameter-estimation are consistent with the results obtained from system characterization via Volterra Kernels (which were reported in previous studies). It was concluded that the suggested approaches could accomplish a nonlinear system characterization through numerical methods, whereas they avoid theoretical complexities and they have acceptable speed (especially steepest descent algorithm).
Fluid-Structure Interaction in Biological Media / FSI
Farzan Ghalichi; Majid Ahmadlouy Darab; Ahmad Ramezani Saadatabadi
Volume 1, Issue 2 , June 2007, , Pages 111-117
Abstract
In order to compare the aorta-coronary and coronary-coronary bypasses blood flow fields in the Endto-Side Anastomosis, we carried out numerical simulation of three dimensional pulsatile blood flow for 50% stenosis by using FLUENT 5.2.3 software. In this study, the blood was assumed to be as the Newtonian, ...
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In order to compare the aorta-coronary and coronary-coronary bypasses blood flow fields in the Endto-Side Anastomosis, we carried out numerical simulation of three dimensional pulsatile blood flow for 50% stenosis by using FLUENT 5.2.3 software. In this study, the blood was assumed to be as the Newtonian, incompressible and homogeneous fluid. The arterial wall was also considered to be rigid. Non-existence of the secondary flows in the coronary-coronary bypass blood flow fields for various degrees of bypass grafting angles against the aorta-coronary-coronary bypass, return of total blood flow toward upstream in the coronary-coronary bypass three times over a heart cycle, high temporary oscillation in the wall shear stress magnitudes for the aorta-coronary bypass and low wall shear stress magnitudes for the coronary-coronary bypass were of the important results.
Cardiovascular Biomechanics
Nima Hemati; Mohammad Javad Abolhassani
Volume -2, Issue 1 , July 2005, , Pages 35-46
Abstract
Nowadays, various methods have been suggested to measure and monitor blood velocity variation in arteries and veins. Ultrasonic velocimetry is one of these methods, which is based on Doppler shift frequency measurement and the blood flow velocity calculation using Doppler shift signal. Using velocity-time ...
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Nowadays, various methods have been suggested to measure and monitor blood velocity variation in arteries and veins. Ultrasonic velocimetry is one of these methods, which is based on Doppler shift frequency measurement and the blood flow velocity calculation using Doppler shift signal. Using velocity-time curves or frequency spectrum which is system outputs, the abnormal cases and the stenosis degree can be determined. In this study, the design and prototyping of a pulsed Doppler system are investigated. The design consists of analog and digital circuits. The analog section includes Master oscillator, stimulus generator, transmitter, receiver, RF amplifier, demodulator and signal sampling circuits. Analog Doppler signal is then converted to digital codes and transferred to PC via an analog to digital converter card. The controlling of analog circuits is also implemented by the digital control unit. After data being transferred to the PC, data analysis such as fast fourier transform (FFT), monitoring of blood velocity variation with time and computation of two dimensional spectrogram are implemented by a software which was written in the Visual C++6 environment. In order to test the system, a string Doppler phantom with full electronic control was built. This phantom also can be used to test and control the quality of the other clinical ultrasonic Doppler systems.
Cardiovascular Biomechanics
Faramarz Firouzi; Nasser Fatouraee; Siamak Najarian
Volume -1, Issue 2 , June 2005, , Pages 129-142
Abstract
Nowadays in the industrial world, because of increase of heart transplantation demand, long-term ventricular assist devices (VAD) are more needed. Implantable sac-type is one of the newest of them producing pulsatile flow. In this research, three different models of sac-type VAD are numerically simulated. ...
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Nowadays in the industrial world, because of increase of heart transplantation demand, long-term ventricular assist devices (VAD) are more needed. Implantable sac-type is one of the newest of them producing pulsatile flow. In this research, three different models of sac-type VAD are numerically simulated. Simple motion is supposed for moving wall in model 1. In model 2, the motion of moving wall is assumed wavy form to study the effect of moving wall form on blood flow. In model 3, the pressure boundary condition is added to model 2. In this model, the effect of actual blood pressure on flow pattern is considered. Results of each model demonstrate the viscose term of blood flow stresses applied to the membrane is negligible, and only pressure term is effective. However, the motional pattern of membrane and also applied pressure on boundary are approximately ineffective on blood flow pattern.
