فصلنامه مهندسی پزشکی زیستی
سال یکم شماره 2 (تابستان 1386)

A new filter was designed and approved for speckle noise removal in sonography images. In this filter, a new idea is used by using neural network learning, fuzzy information and genetic algorithm optimization. The multi-layer perceptron neural network with binary weights is used in this filter. The neighborhood window of each pixel is used as input statistical features to estimate the noise level. Then it is fuzzificated and justified by simple fuzzy rules. The membership function width and network weights are optimized by on-line genetic algorithm. The on-line algorithm contains one individual, defined as a queen. In this algorithm, the next generation is created by using only the mutation operator. The performance of this filter was compared with the other speckle noise reduction techniques such as the median and homomorphic Wiener filters. Indeed, our proposed method is able to effectively remove speckle noises while preserving the quality of fine details in the image data better than the other methods. In this system, two classic and on-line GAs are used. The classic algorithm includes 50 strings. The results showed that both of the algorithms are the same in terms of noise reduction but the classic one is slower than the other one.

Modeling of blood flow and arterial wall in large arteries such as carotid artery, using ultrasonic measurements, allows non-invasive evaluation of clinically interesting homodynamic variables. In this study, a nonlinear mathematical model for the pulsatile arterial flow is proposed using the approximation of “local flow” theory. The blood velocity profile, the pressure gradient and the elastic modulus can be calculated using the model by measuring instantaneous radius and center-line blood velocity. An original mathematical model of pressure gradient in a tapered and elastic tube, using center-line blood velocity, is presented. A Newtonian incompressible Navier-Stokes solver coupled with elastic or visco-elastic arterial wall model is developed to solve the equations of model. The results of modeling and simulation indicate that the approach can estimate the elastic modulus of arterial wall from ultrasonic data. There is a good agreement between the computed arterial wall elasticity and the measured one. The method presented is relatively simple to implement clinically and can be taken as a new diagnostic tool for detecting local vascular change.

In this research, the influence of NaH2PO4.2H2O with different concentrations on setting time and compressive strength of bone cement based on hydroxyapatite was investigated. Hydroxyapatite cement is of calcium phosphate bone cements, which can be considered as the best substitute for hard tissues. The powder phase of the cement was prepared from various compositions of calcium phosphates such: tricalcium phosphate (TCP), calcium carbonate (CaCO3) and montite (CaHPO4) as constant and the liquid part using NaH2PO4.2H2O solution with different concentrations. The influences of liquid/powder ratio L/P (ml/g) was investigated on the initial and final setting times and compressive strengths of the cement. According to the obtained results, with optimum concentrations of the liquid phase, this cement seems suitable for clinical applications.

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.

Simple cells in primary visual cortex respond to the local, oriented edge segments within their receptive fields. In this study, we present a new edge detection method based on the computational model of these cells. Firstly, the response of a set of simple cells for a number of different preferred orientations are calculated. Then, the intensity gradient for each pixel is obtained using the linear summation of these responses. Some parameters of simple cell computational model are calculated in such a way that a set of goals (good detection, good localization and only one response to a single edge) achieving for the resulting operator. Considering the properties of medical images, the proposed operator is useful for medical image edge detection. The synthesis and medical images with their associated ground truth edge maps are used to assess performance of the proposed method. The results obtained from the proposed method are found to be better and more stable with respect to the input parameters than those from many well known edge detectors (e.g. Canny edge detector).

Considering the life threatening consequences of the cervical spine injuries, the study of its biomechanical behavior has become important. The most common axis (second cervical vertebra) injury is called odontoid fracture, the majority of which is type II or dens fracture. In this study, an exact 3D finite element model of axis was developed and analyzed. To evaluate the stress distributions in the odontoid process during type II injuries, pressure loads were applied on the dens at locations where it is likely to come into contact with the surrounding neck construct. Results indicate stress concentration in the odontoid junction with the vertebral body, which suggests that there is a possibility of occurring type II fracture in the case of impaction of odontoid with atlas anterior arch, lateral masses and transverse ligament.

Hydroxyapatite (HA) is a well known candidate for many applications in dentistry and medicine such as bone replacement and regeneration and coatings for medical implants. Nano-crystalline HA exhibits improved mechanical properties and biocompatibility. To optimize the benefits of nano-sized precursors, the particles must be of a uniform shape and size and have minimum degree of agglomeration. The aim of this study was to synthesize of nano-crystalline HA via the biomineralization route. For this purpose, an Iranian strain of Serratia (Serratia marcescens PTCC 1187) was utilized for the synthesis of nano-crystalline HA. The strain was cultivated. Then the pellet of S. marcescens PTCC 1187 was separated and exposed to Glycerol 2-phosphate and Calcium chloride. After 14 days of incubation at 37oC, the white precipitated material was separated. After drying and calcination at 600oC the powder was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) techniques. The results showed that nano-structured HA powder was synthesized and the crystallinity of the powder was relatively high according to the standard. The particles of the powder were single crystal with the size of 25-30 nm. Moreover, the shape and size of the particles were relatively uniform and the agglomeration was lower comparing to the conventional methods. This powder could be used in the regeneration of bone defects, fabrication of medical, dental implants and also as a vector for pharmaceuticals and biological materials such as the genes.