فصلنامه مهندسی پزشکی زیستی
سال یکم شماره 1 (بهار 1386)

The methods of focusing ultrasonic waves in order to apply hyperthermia cancer therapy have studied and a transducer capable of focusing waves on cancerous tissues with the aid of its piezoelectricelements has introduced. The amount of absorbed energy was computed by solving numerically the acoustic pressure equation using Rayleigh-Summerfield Integral, with the intention to determine the optimum spatial array of piezoelectric elements for energy concentration. In order to control the treatment procedure, the numerical solution of Bio-heat Transfer Equation (BHTE), along with the finite-element simulation of thermal energy distribution in a cervix cancerous tissue is considered.

Blood is one of the vital fluids of the human body. Measurement of its viscosity and other properties is very important in detecting and understanding different cardiovascular diseases. In this study, the blood flow in a concentric cylinder viscometer was simulated numerically. The blood flow patterns were analyzed by applying different rotational speed of inner cylinder. Creation of a Couette flow, end effects and suitable rotational speed limit were analyzed. The amount of the torque applied to the inner cylinder which prevents the generation of the Taylor vortices was also predicted. From the obtained results, one can conclude that these vortices were not as important as the end effects were. In order to keep the blood sample temperature within a constant and acceptable range a thermal bath was used. Heat removal rate with different inflow rates of coolant was also predicted numerically.

Recently there are studies in developing new methods to increase bacterial adhesion onto polymeric surfaces that are used in biological application such as cell-based biosensors. In this study the surface of polyethylene terephthalate (PET) films were irradiated using CO2 and KrF excimer pulsed lasers and adhesion behavior of Escherichia coli k-12 (E. coli K-12) bacteria onto the irradiated surfaces was studied in vitro. The changes in the surface properties due to laser irradiation were characterized by scanning electron microscopy (SEM) and contact angle measurement. The results showed that laser treatment changes surface morphology and surface hydrophilicity. The number of bacteria that were adhered onto the surfaces was quantitatively investigated by fluorescent staining, microscopic observations and counting through Image Proplus software. The results showed that the number of adhered E. coli K-12 bacteria onto the irradiated surfaces by both CO2 and KrF lasers in comparison with unmodified surfaces was increased.

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).

Amorphous carbonated calcium phosphates (ACCPs) with different carbonate contents and Ca/P ratios were reproducible synthesized by the reaction parameters as low temperature, high pH value, using initial solutions of calcium and phosphate at low concentrations, and various amounts of carbonate, as well as freeze drying of the precipitates. The addition of carbonate to the solutions led to form precipitates with higher Ca/P ratios with respect to the initial solutions. Heat treatment of freezedried ACCPs at 500 °C had no influence on their amorphous structure. The results of elemental carbon and thermal analysis showed that the carbonate may be eliminated in a wide range of temperature (500−1150oC). Dissolution rate of ACCPs in the simulated bone resorption medium was dependent to the contents of carbonate and remaining water. Dissolution rate of the specimens with higher carbonate contents was controlled by the carbonate content, but the amount of remaining water had major influence on the dissolution rate of the precipitates with lower carbonate contents. The dissolution kinetics was found to follow a shrinking-core model, with product layer as the ratedetermining step. Formation of an amorphous calcium phosphate and/or thermodynamically desirable dicalcium phosphate dihydrate as possible product layer prevents complete resorption of ACCPs under bone resorption conditions, and promotes osteoblastic activation process through nucleation and growth of biological apatite.

Ventricular Fibrillation (VF) is a dangerous abnormality in the heart activity. During the VF, well known shape of electrocardiogram (ECG) signal changes to a pseudo-noise waveform. Recent researches have depicted that VF is not a noisy signal. The characteristics of VF and chaotic signals are the same. In this research, these characteristics were studied and used for discriminating the VF signal from the other electrocardiogram signals. Three types of electrocardiogram signals including VF, Tachycardia and Normal ECG were used for training and testing a back propagation neural network. We used these signals in three stages. At the first stage, the power spectrum of signals was used for training and testing the neural network. Time Series signals were used in the second stage. The result of the first experience was better than the second. At the third stage, we used surrogate technique to enrich the training signals in the time domain. The surrogate technique is a method which has been used in the chaotic systems. By using these new generated signals for training the neural network, the results of classification were extremely improved. Furthermore, the results of simulations showed that the chaotic dynamic of VF signal is a time dependant one.

Jaundice (hyperbilirubinemia) is a common disease in newborn babies. Under certain circumstances, elevated bilirubin levels may have detrimental neurological effects. In some cases, phototherapy is needed to lower the level of total serum bilirubin, which indicates the presence and severity of jaundice. Recently, diagnosis and treatment modeling of disease have been considered by many researchers. In this paper, we present two models for classification and prediction of neonatal jaundice. The models are based on recorded data of Iranian Neonates. This study is oriented on the basis of following procedures: a short review on physiology of Jaundice, and then description of the models. Two three-layer feed forward neural networks were used in the modeling. The neural network model for classification is able to specify the type of jaundice, and the model for prediction can evaluate the risk of jaundice for newborns. These models can be used to decrease the risk in the critical cases as well as the cost of treatment.