Takeharu Hoshi

Development of an integrated needle insertion system with image guidance and deformation simulation

OBJECTIVE The purpose of our work was to develop an integrated system with image guidance and deformation simulation for the purpose of accurate needle insertion. METHODS We designed an ultrasound-guided needle insertion manipulator and physical model to simulate liver deformation. We carried out an in vivo experiment using a porcine liver to verify the effectiveness of our manipulator and model. RESULTS The results of the in vivo experiment showed that the needle insertion manipulator accurately positions the needle tip into the target. The experimental results also showed that the liver model accurately reproduces the nonlinear increase of force upon the needle during insertion. DISCUSSION Based on these results, it is suggested that the needle insertion manipulator and the physical liver model developed and validated in this work are effective for accurate needle insertion.

Deformation simulation using a viscoelastic and nonlinear Organ model for control of a needle insertion manipulator

This paper shows the viscoelastic and nonlinear organ deformation model for organ model-based control of needle insertion, in which the deformation of an organ is calculated intraoperatively and the needle is manipulated with organ deformation taken into consideration. An organ model including such detailed material characteristics is important to achieve the control method in question. Firstly, the material properties of the liver are modeled from the measured data and its viscoelastic characteristics are represented by differential equations, including the term of the fractional derivative. Nonlinearity in terms of the fractional derivative was measured, and modeled using the quadratic function of strain. Next, a solution of an FE model using such material properties is shown. We use sampling time scaling property as the solution for the viscoelastic system. The solution for a nonlinear system using the Modified Newton-Raphson method is also shown. Finally, the organ deformation, assuming the needle is inserted, is simulated using an organ model and the overall deformation and distribution of the strain is computed in these simulations.

In vitro validation of viscoelastic and nonlinear physical model of liver for needle insertion simulation

Needle insertion treatments require accurate placement of the needle tip into the target cancer. However, it is difficult to insert the needle into the cancer because of cancer displacement due to the organ deformation. Then, a path planning using numerical simulation to analyze the deformation of the organ is important for the accurate needle insertion. The objective of our work is to develop and validate a viscoelastic and nonlinear physical liver model. First, an overview is given of the development of the physical liver model. Second, the experimental method to validate the model is explained. In-vitro experiments that made use of a pigpsilas liver were conducted for comparison with the simulation using the model. Results of the in-vitro experiment showed that the liver model reproduces (1) the relationship between needle displacement and force during needle insertion; (2) velocity dependence of needle displacement and force when a puncture occurs; and (3) nonlinear and viscoelastic response of displacement at an internally located point displacement, with high accuracy.

Viscoelastic and Nonlinear Organ Model for Control of Needle Insertion Manipulator

This paper shows the viscoelastic and nonlinear organ deformation model for organ model-based control of needle insertion, in which the deformation of an organ is calculated intraoperatively and the needle is manipulated with organ deformation taken into consideration. An organ model including such detailed material characteristics is important to achieve the control method in question. Firstly, the material properties of the liver are modeled from the measured data and its viscoelastic characteristics are represented by differential equations, including the term of the fractional derivative. Nonlinearity in terms of the fractional derivative was measured, and modeled using the quadratic function of strain. Next, a solution of an FE model using such material properties is shown. We use sampling time scaling property as the solution for the viscoelastic system. The solution for a nonlinear system using the Modified Newton-Raphson method is also shown. Finally, the organ deformation, assuming the needle is inserted, is simulated using an organ model and the overall deformation and distribution of the strain at each element is computed in these simulations.

Developing an Intraoperative Methodology Using the Finite Element Method and the Extended Kalman Filter to Identify the Material Parameters of an Organ Model

It is generally difficult to determine the material values of human tissue to input into an organ deformation model, because the material properties of human tissues are inherently uncertain because of their individual differences. In our work, we developed a promising approach that allows identification of the material parameters of the organ model by using information obtained during surgery. The effectiveness of the method was shown through both numerical and physical experiments. As a result of both experiments, it was shown that the material parameters of the organ model were accurately identified.

Developing a planning method for straight needle insertion using probability-based condition where a puncture occurs

Needle insertion treatments require accurate placement of the needle tip into the target cancer. However, it is difficult to insert the needle accurately because of cancer displacement caused by organ deformation. Therefore, a path planning using numerical simulation to analyze the deformation of the organ is important for accurate needle insertion. The problem in developing a planning method is that puncture conditions, such as the force applied to the needle, is difficult to be decided deterministically, because the experimental data of puncture conditions have variations. Therefore, the purpose of this research was to develop a novel planning method to decide the robust paths of straight needle insertion for various puncture points. The basic idea of this planning method is to consider the puncture condition probabilistic and to evaluate the expected value of needle placement accuracy. First, a probability-based puncture condition was introduced, and then the expected value of needle placement accuracy was defined. Next, the optimization method was developed to search the insertion path in a way that minimizes the expected values of needle placement accuracy. Then, a numerical simulation and evaluation of the planning method was conducted, using a liver-shaped 2D model. Furthermore, an in-vitro experiment was carried out to measure needle placement accuracy from the optimized path. Experimental results show that the planning method realizes needle insertion with a mean accuracy of 1.5 mm.

Developing a system to identify the material parameters of an organ model for surgical robot control

Accurate values of material parameters of human tissue are key elements in a surgical robot system using an organ deformation model. However, it is generally difficult to determine the values of the material parameters of human tissue to be input into the model, because the individual differences of these material properties make them inherently uncertain. In this work, we discuss a method for identifying the values of the material parameters of an organ model. This paper is also concerned with developing a method using the finite element method (FEM) and the extended Kalman filter in order to identify the values of the material parameters of an organ model. The effectiveness of the method was shown through physical experiments using a layered phantom, a three-dimensional deformation model by FEM, and ultrasound imaging equipment. The results of experiments showed that the proposed parameter-identification method improved the reproducibility of the simulation using organ models.

Modeling of conditions where a puncture occurs during needle insertion considering probability distribution

Needle insertion treatments require accurate placement of the needle tip into the target cancer. However, it is difficult to insert the needle into the cancer because of cancer displacement due to the organ deformation. Then, a path planning using numerical simulation to analyze the deformation of the organ and the timing of puncture is important for the accurate needle insertion. In this study, we have explained the modeling of conditions where the puncture occurs. Firstly, this paper shows needle insertion experiments for the hog liver in order to measure the needle force and displacement where the puncture occurs. According to the experimental results, significant variations in puncture force were observed. Accordingly, we proposed a novel condition of the force causing a puncture considering probability distribution. We summarized variations of the puncture force in the experimental data and represented conditions where a puncture occurs with probability distribution models where the force is random variable. In addition, the boundary conditions and liver shapes are considered by analyzing the stress status near the needle. Then, we derived the conditions of the puncture with probability distribution models where the stress is random variable.

Evaluation and comparison of the nonlinear elastic properties of the soft tissues of the breast

As the number of breast cancer patients increases, there is an increasing need for accurate non-invasive methods for the diagnosis of breast cancer. It is possible that the nonlinear elastic properties of soft tissues of the breast can be used as a basis for diagnostic methods. Therefore, we have proposed a robotic palpation system for diagnosis based on the nonlinear elastic properties of tissue. Here, we measured the nonlinear elastic properties of soft tissues of the breast using creep tests and three parameters of the nonlinear elastic model were acquired. Two of these parameters are significantly different among soft tissues of the breast and that the magnitude of these parameters was determined by the tissue structure. These parameters could be used to differentiate between tissue types and aid in the diagnosis of breast cancer.

Quantitative palpation to identify the material parameters of tissues using reactive force measurement and finite element simulation

In this paper we present a new robotic palpation method to perform quantitative measurement of the material parameters of human tissues, for use in medical applications. The proposed method is achieved by the use of a system that integrates a robotic component and a numerical simulation component. The robotic component is used to measure the contact force and displacement at each point on the human body contacted by a robotic probe. The numerical simulation component identifies the material parameters using the proposed method, where two data sources are used, namely, (1) the measured data from the robotic part, and (2) simulated deformation data obtained by the finite element method. In order to validate the proposed system, we report initial results from several phantom tissue experiments, which demonstrate the ability of the system to quantitatively determine the elastic moduli of tissues. We also discuss several potential challenges in the future of the proposed system.