Sharif Digital Repository

In the recent years, medical application of robots has been widely developed. Transforming open surgeries to close surgeries has distinguished this novel method to decrease limitations in this type of surgery. In this procedure, two or three small incisions on the skin are used as guides for robotic instruments to enter the cavity, to improve the surgeon’s manipulation and function in surgery. One of challenges in this field is surgeon’s training for laparoscopic surgery. Surgical simulators are used to solve this problem. Lack of instrument for large organs gripping and tissue palpation loss are existing difficulties in available surgical simulators in such a manner that surgeons has no... 

The application of acoustic waves as a diagnostic tool in medicine is highly regarded. Because of the mechanical and Noninvasive nature of this waves when penetrate in the body will not have any adverse effects on the body. Thus development and operation of these waves is growing every day. If abnormal changes in soft tissues (such as tumors inside the body) is created, by the reflected sound waves easily recognizable although it is experimental, and a little scientific studies have been conducted on the contrast of soft tissue and acoustic waves. Soft tissues of the human body Because of the asymmetric structure has a non-uniform physical and mechanical properties in different directions,... 

In the present dissertation model based grasping of soft tissue with the laparoscopic gripper, tissue deformation under the applied load and control of the tissue-instrument interaction have been studied. As the first step a cantilevered beam under bending and tension has been modeled statically and dynamically using the meshless EFG based method. Results show that an increase in the number of nodes at the displacement boundary and the area of force insertion improves the accuracy of the predicted displacement in the model compared to the analytical solution. In the second step the model is developed for a hemisphere under vertical and lateral compression. Comparison of the deformation of... 

Two methods for simulating material behavior of heart mitral valve leaflet tissue are developed in this thesis, in the finite element setting. First, a mixed pressure-displacement formulation is used to implement the constitutive material behavior with general 3D elements. Second, a shell is formulated that incorporates the 3D material behavior by use of a local plane stress iteration method. Both of these works are based on an existing invariant-based strain energy function that has been experimentally determined for the mitral valve leaflet tissue. Since this material is considered to be nearly incompressible, a mixed pressure-displacement (u/p) formulation is needed to apply the material... 

Surgical simulation systems facilitate a safe and efficient training process by providing a virtual environment in which the trainee can repeat the surgical procedure unlimitedly at different situations. The present study attempted to provide a real time simulation for the grasping procedure of a large internal organ during laparoscopic surgery. A mass-spring-damper model was employed to simulate the nonlinear viscoelastic large deformations of spleen tissue interacting with a triple-jaw large organ grasper. A novel collision detection algorithm was designed and implemented to determine the contact points between the tissue and the grasper jaws. The boundary conditions imposed at the contact... 

Surgical simulators present a safe, practical, and ethical method for surgical training. In order to enhance realism and provide the user with an immersive training experience, simulators should have the capability to provide haptic feedback to the user. Accurate modeling of the interaction between surgical instruments and organs has been recognized as a key requirement in the development surgical simulators. Researchers have attempted to model tool-tissue interactions in a wide variety of ways, which can be broadly classified as (1) continuum mechanics-based,(2) discrete elements-based methods.
This thesis presents an improved model of static Long Elements Method (LEM), a new method... 

Realistic simulation of tool-tissue interactions can help developing more effective surgical training systems and simulators. In this study we used finite element and meshless modeling approaches to simulate the grasping procedure of a large intra-abdominal organ, i.e., kidney, during laparoscopic surgery. Results indicated that the accuracy of meshless method was comparable with that of the finite element, with the RMS errors in the range of 0.8 to 3.4 mm in different directions. The computational cost of the meshless method however, was much less than that of the finite element model. In order to verify the model, a silicon sample was used with the ship kidney geometry. For determination... 

Recently, the deficiency of methods like organ donation and medicine made tissue engineering a prospective method in regeneration of tissues. Despite all of its advantageous like any other method, it has its own weak points. Its major disadvantage is the probability of rejection by the host body. Using proper material and controlling synthesis reactions by researchers decreased the rejection of synthetic scaffolds. But in the case of natural scaffolds due to the range of properties, many tests should be applied on the scaffold prior to implantation in order to evaluate functionality in body. In this research, SDS and TritonX100 has been used to decellulize kidney. Then using uniaxial... 

Cancer is one of the deadliest diseases of the modern era and accounts for 13% of all deaths in humans. Most cancers and lesions in the human body are related to soft tissue. Many soft-tissue cancers and lesions occur in sensitive areas of the body, such as the brain, pituitary, and intestine. The pituitary gland is located in the human head and near the optic nerves. Surgery in a typical way can result in risks such as heat loss of the optic nerve or injuries to healthy tissues due to the sharpness of the surgery tool. One of the alternatives to conventional surgery is water jet surgery. This method minimizes the risks of human error. In the present study, a water jet machine was designed... 

Aside from many advantages of minimally invasive surgery, it has some drawbacks. Surgeons` loss of dexterity dexterity, lack of force feedback and the consequent reduced sensation of forces are some of these drawbacks. Also, surgeons` ergonomically inappropriate posture gets him fatigued, causing hand tremor which is furthermore magnified by the long instruments. Robotic surgery systems have overcome some of minimally invasive surgeries limitations. But still some drawbacks such as high cost of maintenance or lack of haptic force feedback have impeded their widespread application. The high cost of maintenance is mostly caused by instrument changing and sterilization.The main goal of this... 

When the human body is subjected to high accelerations, cardiac function and blood supply to the body can be changed. Due to the complex geometrical and mechanical properties of heart, finite element method is useful way for analysis of response of this structure under different load types. Modeling heart using finite element method requires mechanical and geometrical properties of heart. Soft tissues modeling, such as heart muscle using finite element method is one of the most challenging issues in field of biomechanics. In this thesis, the mechanical properties of heart are obtained by performing experimental compression tests on samples of fresh bovine heart. Using obtained experimental... 

In many modern medical procedures, needle insertion is an inevitable part of the diagnosis or treatment protocols. The accuracy of the needle insertion is adversely affected by a number of factors. A needle, frequently assumed to be flexible, is inserted into a soft tissue and induces complex mechanical interactions that may result in considerable uncertainties. Tissue intrinsic characteristics as well as its deformation and rotation may cause dramatic complexities. This work considers the needle movement inside the tissue from the dynamics and control point of view. The proposed approach can be regarded as an initial step towards automation of needle insertion procedures; it can also be...