فصلنامه مهندسی پزشکی زیستی
سال هفتم شماره 4 (زمستان 1392)

Computationally fast biomechanical models are required to present the actual behavior of soft tissue in real-time simulation. These models are applied in medical diagnosis, surgical planning and training. One of the challenges in the surgical simulation is soft tissue cutting that requires topology changes and elements remeshing in real-time.This paper present a new algorithm for soft tissue cutting using its geometric analysis. This method creates a less number of degrees of freedom and shows a stable simulation that leads in less tissue damage as compared to other methods. According to the simulation results, the proposed algorithm has a relatively high speed. In addition, a mapping method has been proposed that relates physical and visual model and consequently shows a more realistic surgery. In order to achieve a physics based, accurate and reliable force model, Finite Element Method is used. Finally, the proposed algorithm is simulated for three-dimensional soft tissue tumor and evaluated using the SOFA-Framework.

The central nervous system (CNS) uses a redundant set of joints and muscles to ensure both flexible and stable movements. How the CNS faces the complexity of control problem is not still clear. Modular control is one of the most attractive hypotheses in motor control. In this hypothesis, some motor primitives (e.g. muscle synergies) are considered as the building blocks that can be combined to present a vast repertoire of movements. EMG signals are required for extracting muscle synergies and NMF (nonnegative matrix factorization) is one of the most accepted methods for extracting synergies. Due to tonic component elimination of EMG signals involved in reaching movements in vertical planes, the standard NMF method is not applicable to extract muscle synergies. In this paper a modified NMF method, so-called semi-NMF, is applied to resolve the tonic component problem. On the other hand, to improve the accuracy of synergies' estimation and to find the global optimum for the optimization problem, we have proposed using HALS method. The proposed algorithm was applied to the experimental EMG recorded in arm reaching movement in the frontal plane. The results showed a good improvement both in accuracy and repeatability of extracted synergies. In addition, extracted muscle synergies were physiologically interpretable.

During laparoscopy surgery, the surgeon cannot touch the tissues directly by his/her hand. As a result, he is not able to use tactile sensing for evaluating the tissues’ mechanical behavior and diagnosing their normal/pathological conditions. Furthermore in vivo biomechanical characteristics of Intraabdominal soft tissues are among the main data required for surgery simulator softwares. The purpose of this research was to design and analyze a robotic surgical instrument which could grasp and compress the intra-abdominal large soft tissues and provide their force-displacement characteristics. The designed device is analogous to a robotic hand with two fingers, which are opened and closed using a parallelogram mechanism. A combined mechanism, including two connected sliding links and a compensatory cam, are used to prevent the fingers horizontal motion and keep the contact area fixed. The results of the kinematics analysis indicate the efficacy of the designed mechanism to provide pure vertical motion in fingers, parallel to each other. Also, the results of dynamic analysis indicate that, after dimensional optimization, the maximum force required at the actuator is 65 N, to apply a 10 N compressive force to the tissue at the middle of grasping range.

In this article, differences between multichannel EEG signals of artists and nonartists were investigated during visual perception and mental imagery of some paintings and at resting condition using scaling exponent. It was found that scaling exponent is significantly higher for artists as compared to nonartists during the three mentioned states, suggesting that scaling exponent may reflect the influence of artistic expertise. No significant difference in scaling exponent was observed between the visual perception and the mental imagery tasks. In addition, the two groups were classified using scaling exponent of channel C4 and Neural Gas classifier during the visual perception, the mental imagery and the resting condition. The average classification accuracies were 50%, 58.12% and 70%, respectively. The obtained results suggest that discriminability in scaling exponent decreases during the performance of similar cognitive tasks.

Stability is important to prevent falling during occupational and daily living activities. Control parameters such as direction of motion and external load can affect stability pattern. The purpose of this paper was to evaluate the effect of the mentioned control parameters on stability. Time series of lumbar rotation angle in 19 healthy subjects were investigated. Each subject performed spine flexionextension in two different directions of symmetric (sagittal plane) and asymmetric (between sagittal and transverse planes), with two loading cases of 8 Kg weight and load free. To evaluate dynamic stability of repetitive movement, a nonlinear method of largest Lyapunov exponent has been used. After calculating maximum Lyapunov exponent from each of the experimental cases, results of analysis of variance showed a significant difference between symmetric and asymmetric directions (p=0.016). To interpret this result we can suggest higher recruitment of the internal and external oblique muscle groups and higher mechanical constraints in spine during asymmetric tasks. Mean comparison showed that movement in symmetric direction has more instability than the asymmetric case. Moreover, presence of load and interaction between direction and load did not significantly affect local dynamic stability.

Orthodontic specialists interest in study of tooth movement mechanic, such as the relationship between applied force and the rate of tooth movement in orthodontic treatment. It is because of the complexity and variety of factors that can affect orthodontic treatment. The friction force at the contact surfaces with an undetermined magnitude, makes the orthodontic treatment unpredictable. In this study, friction coefficient and forces were investigated in new designed bracket that had beveled edge which has been modeled based on standard bracket. Torque, tip and angulations angles of the brackets slot are designed. Arch wires were modeled by two rectangular and circular cross-sections and the effect of geometry on the stress distribution and the friction force was investigated using Finite Element Method (FEM). The results have showed that the stress concentration generated in the bracket which has been the most curvature, decreased compared to the standard bracket at the contact wire and bracket braces. In addition, results have showed that friction in the beveled edge bracket was significantly decline compared to the standard bracket and also are less than the type with minor curvature. Results of investigation of friction between the two types of round and square wire, have revealed that the round wire has lower friction and confirmed previous studies. Finally, due to the reduced friction in the brackets which have been the most curvature, this type of design is appropriate to decrease friction force.

A secure self-biased remote controller for a drug delivery system, working at 956 MHz, is designed using piezoelectric substrate containing an implantable micropump. For this purpose, the effect of Lithium Niobate substrate on the actuation voltage, signal to noise ratio, insertion loss, bandwidth, and real and imaginary part of the admittance are investigated. The results of analytical calculation and numerical simulation show that the actuation voltage of the Lithium Niobate substrate is about 5.8 V, and the calculated bandwidth is 160 MHz with the signal to noise ratio of 26.52 dB. The security for actuation of the device is assured with Barker code. The insertion loss is equal to 2.1 dB which is adequate for maximum power transfer. Numerical simulation indicates that the generated voltage could create a displacement about 9.3353 nm in the conductive diaphragm, which is enough to ascertain the correct drug delivery by the micropomp. According to the analytical calculations and numerical simulations, the performance of the designed controller is qualified to correctly stimulate the drug delivery device.

Wearable measuring system has major effects onbiomechanics of human movements especially in daily activitiesin order to monitor and analyze the human movements to achievethe most important kinematics parameters. In the recent decade,inertial sensors were utilized by researchers in order todeveloping wearable system for instrumentation of humanmovements. In this study, Sharif-Human MovementInstrumentation System (SHARIF-HMIS) was designed andmanufactured. The system consists of inertial measurement units(IMUs), stretchable clothing and data logger. The IMU sensorsare installed on the human body. The system can be used at homeand also industrial environments. The main features of thissystem are: low cost, low weight, saving data for ten hours andbeing wearable. Furthermore, the software was designed for data acquisition of the IMUs.