Yo Kobayashi

Modeling of friction force based on relative velocity between liver tissue and needle 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 needle insertion simulation to analyze the deformation of the organ is important for the accurate needle insertion. A frictional model for needle insertion simulation is presented in this report. In particular, we focus on a model of frictional force based on the relative velocity between the needle and liver tissue ranging from hyper slow velocity. First, in vitro experiments using hog liver were performed at several relative velocities in order to measure the velocity dependence of the frictional force. Several needle insertion experiments were performed under identical conditions in order to deal with the variance of experimental data. The 60 frictional force data were used to obtain average data at each relative velocity. Second, the model of frictional force was developed using the averages of the experimental results. This model is defined according to the relative velocity ranging from hyper slow velocity. Finally, an evaluation experiment was carried out. The data obtained by the evaluation experiment reveals that the frictional force changes according to the relative velocity between the needle and liver tissue. The experimental results support the validity of proposed model of frictional force.

Temperature dependence of thermal conductivity of liver based on various experiments and a numerical simulation for RF ablation

Radiofrequency ablation (RFA) for liver cancer has increasingly been used over the past few years because RFA is minimally invasive treatment for patients. However, precise control of the formation of coagulation zones is difficult for operators due to inadequate imaging modalities. With this in mind, we have proposed a model-based robotic ablation system using numerical simulation to analyze temperature distributions in the organ to overcome this deficiency. The objective of our work is to develop a temperature-dependent thermophysical organ model to construct a precise numerical simulator for RFA. However, no standard methods exist for obtaining the thermophysical properties of biological tissues, as detailed evaluations of the accuracy of properties obtained from various experiments have not been completed. The purpose of this study was thus to measure and model the temperature dependence of thermal conductivity in hog liver from three representative methods, and to compare these results using our developed numerical simulator to reveal differences in temperature distributions stemming from differences in thermal conductivities.

Enhanced Targeting in Breast Tissue Using a Robotic Tissue Preloading-Based Needle Insertion System

The use of minimally invasive procedures for breast tumor diagnosis and treatment, such as needle biopsy and radiofrequency ablation (RFA), is steadily increasing. Accurate needle insertion requires solving the problems of tissue deformation and target displacement. In this study, we developed a robotic needle insertion method to improve the precision of diagnostic biopsy and RFA treatment. The mechanical probe was designed to reduce tissue displacement by pressing the breast tissue before needle insertion: a technique that is known as preloading. We focused on the needle insertion phase and evaluated the insertion accuracy achieved. Using a numerical simulation model and an actual hog breast, we compared tissue preloaded needle insertion with normal needle insertion. The data obtained with both test systems showed that targeting errors were greatly reduced using preloading-based needle insertion, as compared with normal needle insertion. The procedure is expected to offer a safe and effective alternative to the traditional methods of needle insertion for breast tissue biopsy or RFA. Our study also revealed the relationship between insertion accuracy and preloading probe force.

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.

Estimation of intraoperative blood flow during liver RF ablation using a finite element method-based biomechanical simulation

Radiofrequency ablation is increasingly being used for liver cancer because it is a minimally invasive treatment method. However, it is difficult for the operators to precisely control the formation of coagulation zones because of the cooling effect of capillary vessels. To overcome this limitation, we have proposed a model-based robotic ablation system using a real-time numerical simulation to analyze temperature distributions in the target organ. This robot can determine the adequate amount of electric power supplied to the organ based on real-time temperature information reflecting the cooling effect provided by the simulator. The objective of this study was to develop a method to estimate the intraoperative rate of blood flow in the target organ to determine temperature distribution. In this paper, we propose a simulation-based method to estimate the rate of blood flow. We also performed an in vitro study to validate the proposed method by estimating the rate of blood flow in a hog liver. The experimental results revealed that the proposed method can be used to estimate the rate of blood flow in an organ.

A robotic palpation-based needle insertion method for diagnostic biopsy and treatment of breast cancer

We describe here a palpation-based needle insertion method for diagnostic biopsy and treatment of breast cancer. The mechanical palpation probe locates cancerous tissue from force information and reduces tissue displacement during needle insertion. We compared palpation-based needle insertion to normal needle insertion by numerical simulation of a breast tissue model and by experiments in vitro. The data showed palpation-based needle insertion had a smaller error in both tests. Our findings suggest the procedure is a safe, effective alternative to traditional methods of breast tissue biopsy.

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.

Design of a surgical robot with dynamic vision field control for Single Port Endoscopic Surgery

Recently, a robotic system was developed to assist Single Port Endoscopic Surgery (SPS). However, the existing system required a manual change of vision field, hindering the surgical task and increasing the degrees of freedom (DOFs) of the manipulator. We proposed a surgical robot for SPS with dynamic vision field control, the endoscope view being manipulated by a master controller. The prototype robot consisted of a positioning and sheath manipulator (6 DOF) for vision field control, and dual tool tissue manipulators (gripping: 5DOF, cautery: 3DOF). Feasibility of the robot was demonstrated in vitro. The “cut and vision field control” (using tool manipulators) is suitable for precise cutting tasks in risky areas while a “cut by vision field control” (using a vision field control manipulator) is effective for rapid macro cutting of tissues. A resection task was accomplished using a combination of both methods.

Use of puncture force measurement to investigate the conditions of blood vessel needle insertion.

Central venous catheterization involves venous puncture and catheter insertion for transfusions. Quantitative conditions that facilitate insertion of the needle, such as the angle and velocity of insertion, have not been clarified. We previously developed a robotic system for guiding the needle along a specified puncture path with high precision and are currently implementing a hardware design for a robotic system to assist in blood vessel puncture. In this study, we proposed the insertion angle and velocity for stopping the needle in a blood vessel, assuming that a robotic system such as ours is used during the procedure. We inserted a needle into a segment of porcine jugular vein and obtained the puncture reaction force. Evaluation indices were the magnitude of the sudden decrease in reaction force at the point at which the needle advances and the length of time that the needle is present within the vein. Results indicated that the conditions under which it was easiest to stop the needle inside the vein were an insertion angle range of 10-20 and an insertion velocity of 3mm/s.

Geometry effect of preloading probe on accurate needle insertion for breast tumor treatment

We herein describe a needle insertion method involving tissue preloading for accurate breast tumor treatment. A mechanical preloading probe locates a tumor lesion from ultrasound imaging information and reduces lesion displacement during needle insertion by pressing the breast tissue. We validated the insertion accuracy of this method by numerical simulation and experiments both in vitro and in vivo. For further accuracy enhancement, we evaluated the geometry effect of the preloading probe on needle insertion accuracy by experiments in vitro. We compared the insertion accuracy between insertion with preloading using different probe diameters and normal needle insertion. In addition, we compared insertion accuracy at different tumor depths. The data indicated a tendency for adaptation of larger preloading probe diameters with deeper tumors. This suggests the potential for our method to enhance placement accuracy by real-time geometry regulation.