فصلنامه مهندسی پزشکی زیستی
سال هفتم شماره 2 (تابستان 1392)

The front part of a cell is divided to two regions called lamellum and lamellipodium (lamellipodial). Internal flows in this part plays an essential role for cell migration. Indeed, there are many protein filaments called actin in lamellum and lamellipodium, which induce the cell motion with polymerization in the leading edge of the cell. The actin filaments adhere to the extracellular matrix (ECM) by means of focal adhesions and they have contact by myosin motor proteins. The myosin motor proteins cause actin retrograde and anterograde flow exerted contractile stress on them. The focal adhesions exert frictional stress on the actin filaments. In this work, we developed a two-dimensional continuum model of the fanshaped lamellipodial to obtain the actin retrograde flow. In addition, the actin filaments are assumed as a highly viscous Newtonian fluid. We also investigated the effects of the myosin distribution and cell speed on the actin flow. Our results include actin flow and myosin distribution in the moving cell, and we also illustrate their relation together. These results accord to reported experimentally and numerically data, and are verified with them.

Blood flow parameters are affected by position and shape of the accumulation of low density lipoprotein (LDL) in the layers of the arterial wall, and this phenomenon itself is influenced by infiltration flow of the blood. In this paper, in order to investigate the effect of wall flexibility on the infiltration flow in a pulsatile non-Newtonian blood flow in a symmetric carotid artery stenosis with a two flexible and porous layers, a finite element model with Porous Fluid Structure Interaction (PFSI) method was used and the results were compared to the porous rigid model. Study parameters were investigated in three different stenosis severities. Comparison of the presented results using PFSI model with those of Porous Rigid model showed about 22% decrease in wall shear stress in the stenosis region, about 20% increase in filtration velocity in the pre- and post-stenosis regions of the porous layer, but a slight difference in filtration velocity in the stenosis region.

The purpose of this study was to design, analyze and evaluate an effective low-cost driving mechanism for gait trainer. The crank-rocker mechanism was favored for reproducing the path of foot during gait cycle, considering the type of motion and design parameters such as adjustability for different anthropometries, providing sufficient space for interactions with physical therapist, and simplicity of execution. The dimensions of the mechanism were determined using optimization method while applying appropriate constraints so that the normal gait pattern, particularly of stance phase, was obtained. A 2-D model of the lower limb was developed to simulate the gait of a patient when using the mechanism. Results indicated that with appropriate positioning of the patient, the kinematic and kinetic patterns of the normal gait are reconstructed with no risk of injury. However, there is a high risk of injury of the knee articular surfaces and ligaments, if the patient is positioned only 3 cm higher than designed height.

Nicotine can be measured electrochemically using Cu nanoparticles and CNT-modified glassy carbon electrode. The slow electrochemical oxidation makes it difficult to measure the concentration of nicotine electrochemically using normal electrodes.To improve the oxidation rate, different mediators and chemically modified electrodes have been used. In this experiment, concentration of nicotine in aqueous solution was determined using MWCNT-modified glassy carbon electrode in presence of copper nanoparticles (Cu NPs) as mediator. For this purpose, the glassy carbon electrode (GCE) was modified with suspended MWCNT in dimethylformamaide and Cu NPs was electrochemically deposited on MWCNT-GCE subsequently. Also, experimental parameters affecting the deposition of Cu NPs on MWCNT-GCE such as cycles, copper salt concentration and scan rate were found to be optimum at 20 cycles, 1.75 μmol L-1 and 100 mVs-1 respectively. Finally, the modified electrode was characterized by cyclic voltammetry and successfully used to measure the concentration of nicotine in aqueous solution.

In this study, electroencephalogram (EEG) signals have been analyzed in positive, negative and neutral emotions. Here it is supposed that the brain has different independent sources during an emotional activity which will be extractable by Independent Component Analysis (ICA) algorithm. For resolving the illposeness problem of extracted components by ICA algorithm, first these sources were sorted by Shannon entropy and then the features of Katz fractal dimension and the first local minimum of the mutual information based on the time delay (tau) have been extracted for representing determinism. The results show that the determinism ratio of the sorted sources has significant difference during the time in three emotional states: positive, negative and neutral. The determinism ratio increases in neutral, negative and positive emotional states, respectively.

Registration of preoperative images to intra-operative patient space is a crucial step in image guided surgery for tracking surgical tools relative to patient’s anatomy. In image guided spine surgery, due to the difference in patient’s positioning in preoperative imaging, compared with intra-operative situation, there is a difference in spine curvature in these two positioning which means that a single rigid registration is not sufficient for registering the whole spine and it is necessary for each vertebra to be registered separately as a rigid body and with it’s appropriate transformation parameters. The registration was carried out using ICP algorithm. For evaluating the registration, TRE was calculated in the pedicle of the vertebra which is the target in pedicle screw insertion. In order to optimize the TRE this study was focused on the factors affecting TRE including different configuration of landmarks used in registration and the registration algorithm. Optimal configurations for the landmarks used in the registration were proposed and FLE for the point pairs were included in the registration algorithm to increase the registration accuracy. The results indicate a total improvement of 45% in the registration accuracy by optimizing the landmarks’ configuration and the registration algorithm.

Acute hypotension episodes (AHEs) are one of the hemodynamic instabilities with high mortality rate that is frequent among many groups of patients. Prognosis of acute hypotension episodes can help clinicians to diagnose the cause of this physiological disorder and select proper treatment based on this diagnosis. In this study two groups of features, physiological and chaotic features, were extracted from the physiological time series to be applied for prediction of AHEs in the future 1 hour time interval. The best set of the features from the extracted features were selected using Genetic Algorithm (GA) and were classified by SVM. The prediction accuracy for physiological features was 87.5% and for chaotic features was 85%. In order to improve prediction accuracy, physiological and chaotic features were employed simultaneously in feature selection and the best combination of these features was selected by GA and classified by SVM. The best prognosis accuracy, which was achieved in this study by classification of the selected features, was 95% that was better than other previously studies on the same database.

Segmentation divides an image to some subdivisions where which of ones has similar intensity gray levels. Among clustering methods fuzzy c-means (FCM) clustering has been frequently used for segmentation of medical images. However, this algorithm doesn’t incorporate spatial neighborhood information in segmentation. This approach is very susceptible to nuisance factors. Therefore this paper proposes a Gaussian spatial FCM (gsFCM) to MR image segmentation. Proposed method has less sensitivity to noise specially in tissue boundaries, angles, and borders than spatial FCM (sFCM). Furthermore by the suggested algorithm a pixel which is a separate tissue from structurally point of view for example a tumor in primary stages of its appearance, has more chance to be a unique cluster. Applying quantitative assessments using Jaccard similarity index, Dice coefficient, and other validation functions on FCM,sFCM and gsFCM approaches show efficient performance of the proposed method. In this research the ISBR data bank is used for simmulations.Moreover in medical applications getting patient condition and information with fast methods is very important especially in emergency circumstances. Therefore all effective agents in patient health must be fast even medical algorithms such as clustering ones . Hence in this paper to decrease the time of convergence considerably and decline the number of iterations significantly, cluster centroids are initialized by an algorithm.