Full Research Paper
Biomedical Image Processing / Medical Image Processing
Effat Yahaghi; Yashar Nohi; Amir Movafeghi; Hamid Soltanian Zadeh
Volume 4, Issue 1 , June 2010, Pages 1-11
Abstract
Magnetic resonance imaging (MRI) is a non-ionizing method for identification and evaluation of soft tissue lesions. Perfusion MRI evaluates soft tissues by measuring changes in magnetization of water molecules due to a contrast agent. To this end, concentration curves in the plasma and tissue are estimated ...
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Magnetic resonance imaging (MRI) is a non-ionizing method for identification and evaluation of soft tissue lesions. Perfusion MRI evaluates soft tissues by measuring changes in magnetization of water molecules due to a contrast agent. To this end, concentration curves in the plasma and tissue are estimated by MRI and effective longitudinal relaxation time (T1eff) of the tissue was calculated. To interpret the results, the effects of water exchange on the effective longitudinal relaxation time should be studied. This work presents such a study in which the equations of two- and three-compartmental models of rat brain tissue are solved using Hion and Runge-Kutta numerical methods for different input functions and simulated by Monte Carlo method. Since the exchange of water and contrast agent among different tissue compartments is a diffusion phenomenon, Monte Carlo method is applicable. Results of the numerical methods were compared with those of Monte Carlo simulation. The results of the two methods were almost identical with a maximum relative difference of less than 1%. In this work, concentration of contrast agent in plasma is estimated from MRI of a rat brain tissue. This data is used in the Monte Carlo method to obtain T1eff and exchange rate constants. An advantage of our method is that T1eff is obtained from real data and not from the curve fitting method as commonly used. We derive concentration of contrast agent as a function of time in extravascular space for different constants (K). Then, the curves of simulated and real data were compared to obtain the exchange rate constant of each compartment. The results showed that K of an abnormal tissue was larger than that of the normal tissues. As such, this parameter may be used for diagnosis and treatment of the soft tissue diseases.
Full Research Paper
Bioheat Transfer
Seyed Alireza Zolfaghari; Mehdi Maerefat; Amir Omidvar
Volume 4, Issue 1 , June 2010, Pages 13-21
Abstract
Generally, most of the human thermal response models are dependent upon a narrow range of personal/environmental parameters. In other words, the effects of other parameters such as eating foods are not considered in these models. On the other hand, previous studies have indicated that the overall thermal ...
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Generally, most of the human thermal response models are dependent upon a narrow range of personal/environmental parameters. In other words, the effects of other parameters such as eating foods are not considered in these models. On the other hand, previous studies have indicated that the overall thermal condition of the body can be significantly affected by eating cold or hot foods. In the present study, the time-dependent thermal response of the human body is simulated with considering the effect of eating hot/cold food. This simulation is performed by adding an extra term to Gagge’s transient model. In this study, three thermal conditions of the human body (hot, neutral and cold) are considered and the effects of eating hot/cold food are investigated under the mentioned conditions. Results indicate that the effects of eating hot or cold food are not negligible during the eating time and also in a period of time after that. At the neutral condition, the human thermal sensation is more sensitive to hot food than to cold ones. Eating hot food changes the body thermal sensation from neutral to hot. But, eating cold food would not make significant changes in the thermal sensation of the body. Results also show that cold food changes the body core temperature more than hot food. While hot food influences the skin temperature significantly.
Full Research Paper
Cell Biomechanics / Cell Mechanics / Mechanobiology
Seyed Abed Hosseini; Mohammad Ali Khalilzadeh; Seyed Mehran Homam
Volume 4, Issue 1 , June 2010, Pages 23-31
Abstract
Various stressful stimuli have different effects on health, decision making, creativity, learning and memory. Understanding human mental states such as stress can prevent its long-term side effects on the body and mind. This study deals with the responses of the neural and hormonal systems to stress ...
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Various stressful stimuli have different effects on health, decision making, creativity, learning and memory. Understanding human mental states such as stress can prevent its long-term side effects on the body and mind. This study deals with the responses of the neural and hormonal systems to stress using the brain cognitive map in this state and simulates the behavior of the CA1 cell calcium channels with electrophysiological equations in the NEURON software. During stress, the glucocorticoids hormones secreted by the adrenal gland cortex reach the hippocampus through blood flow and by activating glucocorticoids receptors, influence the calcium channels dynamics, especially the L-type and increase calcium entry into CA1 cells. This behavior, testify to the reduction of the calcium removal rate in the cells which leads to exponential decrease in cells firing rate and number of spikes and an increase in the sAHP current range. L-type calcium currents in hippocampus region are effective mechanisms during stress. Comparing the research results in two situations, the cell under control and the cell under stress, shows that the model is consistent with some basic observations of stress.
Full Research Paper
Biomimetics
Saeed Rashidi; Seyed Mohammad Reza Hashemi Golpayegani; Ali Fallah; Farzad Towhidkhah
Volume 4, Issue 1 , June 2010, Pages 33-44
Abstract
In drawing movements, the constraints imposed on the trajectory geometry properties and kinematics are known with two laws: 2/3 power law and isochrony phenomenon. In this paper experiments have been designed to study the relation between two empirical laws in straight and curved patterns of drawing ...
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In drawing movements, the constraints imposed on the trajectory geometry properties and kinematics are known with two laws: 2/3 power law and isochrony phenomenon. In this paper experiments have been designed to study the relation between two empirical laws in straight and curved patterns of drawing movements in 16-18 years old subjects. Providing two models of power is indicated that in drawing movements, invariant features can be defining. These features are independent of subject, direction and size of trajectory and together they can simplify the role of the upper motor control system and decrease the degrees of freedom and the computational complexity.
Full Research Paper
Cell Biomechanics / Cell Mechanics / Mechanobiology
Seyed Hojat Sabzpoushan; Fateme Pourhasan Zadeh; Azar Badangiz
Volume 4, Issue 1 , June 2010, Pages 45-52
Abstract
The heart tissue is an excitable media. Cellular Automata is an approach describing cardiac action potential propagation. One of the advantages of Cellular Automata approach over the differential equations based models is its high speed in large scale simulations. Prior Cellular Automata models are not ...
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The heart tissue is an excitable media. Cellular Automata is an approach describing cardiac action potential propagation. One of the advantages of Cellular Automata approach over the differential equations based models is its high speed in large scale simulations. Prior Cellular Automata models are not able to eliminate flat edges in the simulated patterns or have large neighborhoods. Moreover, they are not able to match the shape of ventricular action potential to the real ones. In this paper, we present a new model which prevents flat edges creation by using minimum number of neighbors. we also rather preserve the real shape of action potential by using linear curve fitting of a well known electrophysiological model.
Full Research Paper
Biomedical Signal Processing / Medical Signal Processing / Biosignal Processing
Sorour Behbahani; Ali Motie Nasrabadi
Volume 4, Issue 1 , June 2010, Pages 53-64
Abstract
The analysis of EEG signals plays an important role in a wide range of applications, such as psychotropic drug research, sleep studies, seizure detection and hypnosis processing. From years ago hypnosis was known as a method to help the patients in different fields such as reduction of stress, leaving ...
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The analysis of EEG signals plays an important role in a wide range of applications, such as psychotropic drug research, sleep studies, seizure detection and hypnosis processing. From years ago hypnosis was known as a method to help the patients in different fields such as reduction of stress, leaving bad habits, pain control and etc. EEG signals during pure hypnosis would differ from those recorded in the normal no hypnotic conditions. There are several methods for analyzing the EEG signal and similarity index method is one of the famous methods in this branch. In this paper the features of EEG signal of three groups of people with different hypnotizability during hypnosis (Fractal, Wavelet Entropy, Frequency Bands) from left-right and frontal-back lobes were extracted and analyzed using Fuzzy Similarity Index Method to find whether there are any significant relations between the function of these hemispheres and hypnotizability degree. Finally after detecting the significancy, we used the selected features were used to classify the subjects into three groups of hypnotizability. The best classification accuracy was obtained 94% (for two classes of features 1. entropy, Higuchi, high frequency, 2. energy and entropy) and the lowest was 87.5% (for entropy, Higuchi and low frequency features).
Technical note
Cardiovascular Biomechanics
Ahmad Ramezani Saadatabadi; Majid Ahmadlouy Darab; Farzan Ghalichi; Ataollah Kamyabi
Volume 4, Issue 1 , June 2010, Pages 65-72
Abstract
This study aimed to simulate three dimensional pulsatile Newtonian blood flow in End-to-Side anastomosis of Aorta-coronary bypass using ascending aorta velocity flow wave as graft inlet and left anterior descending coronary artery (LAD) velocity flow wave as coronary inlet for 50% symmetric stenosis. ...
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This study aimed to simulate three dimensional pulsatile Newtonian blood flow in End-to-Side anastomosis of Aorta-coronary bypass using ascending aorta velocity flow wave as graft inlet and left anterior descending coronary artery (LAD) velocity flow wave as coronary inlet for 50% symmetric stenosis. We have supposed that LAD walls were rigid and had no spatial mobility due to heart beats. In order to investigate the graft angles effects on blood flow, especially on the wall shear stress magnitudes, 20, 30 and 40 degrees graft angles were used. Using ascending aorta and LAD pulses simultaneously as boundary conditions for the first time is one of the important features of this study because already these boundary conditions have not been used simultaneously. We considered prograde flow effects. Appearance of recirculation flows in various degrees of grafting angles, existence of secondary flows and increased in their effects specially in pulses deceleration phase, existence of double core helical flows and increase in their intensify specially at the systole peak and the rise in the spatial wall shear stress gradient by increasing in the graft angle are some of important results of this study. Finally, according to our assumptions we suggest 20 to 30 degrees as desired angles for grafting.
