فصلنامه مهندسی پزشکی زیستی
سال دهم شماره 2 (تابستان 1395)

Cancer is the third leading cause of death in Iran after cardiac diseases and car accidents. Mathematical and computational models are great help to better understand cancer related phenomena. It may even improve common therapies or introduce new therapies. In this paper, a new multiscale cellular automata model of tumor growth based on the tumor micro-environment is introduced. Two separate square lattices are presumed for metabolic and cellular spaces. One of the following four states can be devoted to each cell in the cellular lattice: proliferating cancer, non- proliferating cancer, necrotic, and normal cells. Changing the cell's state and tumor growth is discussed in this lattice. However, production/consumption, and the diffusion of nutrients (oxygen and glucose) and also waste products including lactic acid are studied in the metabolic lattice. In this study, we determined the stochastic rules of altering the states of each cell based on the concentration rates of nutrients and lactic acid. The growth fraction and necrotic fraction were used as output parameters beside a 2-D graphical display of growth. The changes in the level of nutrients in the metabolic lattice and the effect of acidity on the growth of tumor have been reported in this paper. Our simulations faithfully reproduce the in vivo experimental observations reported for cholangiocarcinoma.

Nowadays, the use of dental implants in people with osteoporosis is increasing. The consequences of osteoporosis can be important to the success of osteosynthesis devices, prosthetics and dental implants. Using bisphosphonates, which with impressing bone remodeling and decreasing bone catabolic activity lead to increase bone formation can be used as a solution to increase bone density in patients with osteoporosis, which normally osteoporosis is considered as a risk to the acceptance of dental implants by alveolar bone. This study examines the effect of different concentrations of bisphosphonates on bone remodeling. By improving bone remodeling model and taking into account the drug concentration effect on bone resorption, drug effect will be considered. For this purpose, 5, 10 and 20 mg of alendronate per implant and control sample are simulated for a period of 360 days. By comparing the results with control sample, with increasing the drug dose, decrease in bone stress, increase in bone density and thus increase in young's modulus was observed.

A two-dimensional-in-space mathematical model of amperometric micro biosensors with selective and perforated membranes has been proposed and analyzed. The model involves the geometry of micro or nano meter holes partially or fully filled with an enzyme. The model is based on a system of the reaction-diffusion equations containing a nonlinear term related to the Michaelis-Menten enzymatic reaction. In this study, in order to generate general equation, first, dimensionless parameters are introduced and then by replacing them into governing equation are converted to dimensionless equations.The general equations have been solved numerically in 2D space.. Using numerical simulation of the biosensor action, the influence of the geometry of the holes as well as of the filling level of the enzyme in the holes on the biosensor response was investigated. For this purpose three different geometries including cylindrical, upright circular and downright circular cone for cavities are considered and the impact of these geometries on the response of the biosensor in different levels of enzyme are obtained. Biosensor's respond based on rate of enzyme level variations to slope of the cone variations are determined. In the biosensor, as the level of enzyme rises in all three geometries, the biosensor output current increases. Under the same conditions, the sensitivity of biosensor in upright circular cone is more than the other two geometries and increases with a decrease in conical gradient. As long as the enzymatic properties are the same, the more biosensor's number, the more sensitivity.Moreover, a concept known as reduced dimensionless current is introduced by providing and calculating dimensionless current in the biosensor.

It is a common approach to diagnose a disease based on the tongue in Traditional Chinese Medicine. In this paper, a noninvasive imaging of tongue whose surface papilla change in diabetics is used to detect the disease. The required images have been provided by Parsian specialized clinic of Mashhad. In the sampling procedure, the diabetics, healthy individuals and those suspected of diabetes with both sexes and different age groups were considered. After imaging, tongue region was segmented based on two active contour models; then extended local binary patterns features, statistical features of the tongue texture, Color Moments in different color spaces were extracted from the segmented region. After feature extraction, diabetics, healthy and suspected of diabetes were detected using extreme learning machine classification. The proposed method obtained a precision of 97.7% for the current database. Experimental results show the efficiency and responding time of the proposed method compared to other noninvasive methods.

In this paper a new idea is suggested for designing an appropriate bio-impedance sensor in the form of a biopsy forceps to measure the electrical properties of the tissues inside the body. First, by analytically solving the Laplace equation for wedge-shaped tissue in the mouth of the forceps, the relationship between electric potential (results from excitation current) in different points on the tissue surface and the electrical properties of the tissue are obtained. Then, to evaluate the designed bio-impedance forceps using the finite element method and the experimental data obtained for different tissues by Gabriel et al., modeling and simulation were done and it was found that the voltages obtained for all of the tissues inside the mouth of the forceps at different frequencies from 50 Hz to 5 MHz, are consistent with that of the analytical method. To investigate the influence of the opening angle of the forceps, measurements were done at different angles and it was found that for small opening angles, measurements are more accurate. Also, electrical properties were measured by changing the size and shape of the tissue and it was found that the designed forceps is non-sensitive and robust to the changes of the volume and shape of the tissue. A prototype of the designed bio-impedance forceps was fabricated. The forceps was experimentally validated by measuring conductivity of the Phosphate Buffered Saline (PBS) solution with different concentrations at frequency range of 50KHz to 1MHz using an impedance analyzer system. To examine the accuracy of measured conductivity values, the Van Der Pauw method was implemented and electrical conductivity of the PBS was measured again. Results showed that measured conductivities by means of the bio-impedance forceps were accurate with an error less than 4%.

A novel computerized tomographic (CT) imaging structure based on the theory of compressed sensing (CS) is proposed. The main goal is to mitigate the CT imaging time and thus x-ray radiation dosage without compromising the image quality. In this study, we propose to use a novel dictionary in compressed sensing algorithm. Our dictionary is an optimal combination of Wavelet Transform (WT), Discrete Cosine Transform (DCT), and Total Variation (TV) transform. We utilize three quality assessment metrics including mean square error (MSE), peak signal to noise ratio (PSNR) and structural similarity (SSIM) indices to quantitatively evaluate the reconstructed images. The results show that the proposed method can generate high quality images with less artifacts while preserving edges when fewer number of view angles are used for reconstruction in a CT imaging system. This is in comparison with those results obtained from other reconstruction algorithms in view of the reconstructed image quality.

Increasing the cardiovascular disease had led to the researchers to investigate the blood flow more than before. In this article the effects of artery elasticity on hemodynamic parameters with concerning the interaction between blood and the vessel’s wall had been investigated. The wall shear stress had changed with different times and cannot send the congestion of the vessels. From this point the oscillatory shear index had been said the shear stress without the time average. In this study a 3D model from the left coronary bifurcation with 4 models of wall had been investigated. The result from a pulsatile flow from a non-newtonian flow with the method of two ways coupling by using the method of arbitrary Lagrangian–Eulerian had been calculated. The observation had showed a 13 percent decreasing in the profile of velocities at the bifurcation place in that in the hyperelastic model had the highest subtraction. Also by increasing the toughness of the wall the velocity profile and oscillator shear stress were increased. The average shear stress in the model of rigid had showed the 28 percent difference in comparison with the hyperelastic model. By comparing the results with clinical data showed that, the places with average shear stress 1.10 pa and less than that with presenting the oscillatory shear index is more than 0.3 that can be a potential dangerous places in forming atherosclerosis oscillatory shear index plaque especially in the posterior after the bifurcation. Meanwhile in the hyperelastic model the results are more precise than the other models.

Brain-computer interface system based on Steady-state visual evoked potentials is taken into consideration due to advantages such as simplicity of installation and use of the system, enough accurate and acceptable Information transfer rate. In addition to these benefits, short processing time is also an important criterion to have a system that is applicable in real life and have the ability to use online. In this paper, a method based on standard CCA have been present for recognition of stimulus frequency. The proposed method is performed in two stages, offline and online. In the offline stage, the standard CCA is applied to the SSVEP and sin-cos reference signals. After that, template signals are constructed using weights that generate maximum correlation. In online stage, cross correlation between test signal and each template signals are calculated and the stimulus frequency is recognized. The greater accuracy of frequency recognition and less calculation time at the same time are shown by stimulation result.