Hiroki Takeda

Dimensionless solutions and general characteristics of bioheat transfer during thermal therapy

Abstract The derivation and application of the general characteristics of bioheat transfer for medical applications are shown in this paper. Two general bioheat transfer characteristics are derived from solutions of one-dimensional Pennes’ bioheat transfer equation: steady-state thermal penetration depth, which is the deepest depth where the heat effect reaches; and time to reach steady-state, which represents the amount of time necessary for temperature distribution to converge to a steady-state. All results are described by dimensionless form; therefore, these results provide information on temperature distribution in biological tissue for various thermal therapies by transforming to dimension form.

Development and estimation of a novel cryoprobe utilizing the Peltier effect for precise and safe cryosurgery

We have developed a novel cryoprobe for skin cryosurgery utilizing the Peltier effect. The four most important parameters for necrotizing tissue efficiently are the cooling rate, end temperature, hold time and thawing rate. In cryosurgery for small skin diseases such as flecks or early carcinoma, it is also important to control the thickness of the frozen region precisely to prevent necrotizing healthy tissue. To satisfy these exacting conditions, we have developed a novel cryoprobe to which a Peltier module was attached. The cryoprobe makes it possible to control heat transfer to skin surface precisely using a proportional-integral-derivative (PID) controller, and because it uses the Peltier effect, the cryoprobe does not need to move during the operation. We also developed a numerical simulation method that allows us to predict the frozen region and the temperature profile during cryosurgery. We tested the performance of our Peltier cryoprobe by cooling agar, and the results show that the cryoprobe has sufficient cooling performance for cryosurgery, because it can apply a cooling rate of more than 250 degrees C/min until the temperature reaches -40 degrees C. We also used a numerical simulation to reconstruct the supercooling phenomenon and examine the immediate progress of the frozen region with ice nucleation. The calculated frozen region was compared with the experimentally measured frozen region observed by an interferometer, and the calculation results showed good agreement. The results of numerical simulation confirmed that the frozen region could be predicted accurately with a margin of error as small as 150 microm during use of the cryoprobe in cryosurgery. The numerical simulation also showed that the cryoprobe can control freezing to a depth as shallow as 300 microm.

Load sharing algorithm for transporting an object by two mobile robots in coordination

Abstrucf- In this paper, we propose an object transporting system by two tracked mobile robots in an environment with a slope. In such environment an effect of an external force applied to the object should be considered. We first address dynamic cooperative control algorithm of the robot system without external force applied to the object. Next, we derivc! cooperative control algorithm of the system including the effect of the external force. Then we propose an algorithm of a load sharing among robots in an uneven environment. We apply the proposed algorithm to the experimental system of two tracked mobile robots and illustrate the validity of the proposed algorithm.

Cooling Characteristics of Ultrafine Cryoprobe Utilizing Convective Boiling Heat Transfer in Microchannel

This paper describes a novel cooling system to be applied in cryosurgery. An ultrafine cryoprobe has been developed to treat small lesions which cannot be treated by conventional cryoprobes. The main problem of the ultrafine cryoprobe is the reduction of the heat transfer rate by the small flow rate due to the large pressure drop in a microchannel and the large ratio of the surface area to the volume. In order to overcome these problems, we utilized boiling heat transfer in a microchannel as the heat transfer mechanism in the ultrafine cryoprobe. The objectives of this paper are to develop an ultrafine cryoprobe and evaluate its cooling characteristics. The ultrafine cryoprobe has a co-axial double tube structure which consists of inner and outer stainless steel tubes. The outer and inner diameters of the outer tube are 0.55mm and 0.3mm, respectively. The outer and inner diameters of the inner tube are 0.15mm and 0.07mm, respectively. The inner tube serves as a capillary tube to change the refrigerant from liquid state to two-phase flow. Furthermore, two-phase flow passes through the annular passage between the inner and out tube. The hydraulic diameter of the annular passage is 0.15mm. Furthermore, HFC-23 (Boiling point is −82.1°C at 1atm) is used as the refrigerants. The temperature of the ultrafine cryoprobe was measured. The lowest temperatures were −45°C in the insulated condition and −35°C in the agar at 37°C (which simulates in vivo condition). Furthermore, the frozen region which is generated around the ultrafine cryoprobe was measured 5mm from the tip of cryoprobe at 120s, and resulted to be 3mm in diameter. Moreover, the change of the refrigerant state is calculated by using the energy conservation equation and the empirical correlations of two-phase pressure drop and boiling heat transfer. As a result, the refrigerant state in the ultrafine cryoprobe depends on the external heat flux. Finally, the required geometry of the ultrafine cryoprobe to make high cooling performance is evaluated.Copyright

Collision Avoidance Algorithm for Two Tracked Mobile Robots Transporting a Single Object in Coordination Based on Function Allocation Concept

In this paper, we propose a collision avoidance algorithm for two tracked mobile robots transporting a single object based on a function-allocation concept. In this algorithm, the desired trajectory of the object is given to the leader robot, and the follower robot estimates the desired trajectory of the leader along the heading direction of the follower and generates the motion of the object for avoiding obstacles. We experimentally implement the proposed algorithm in the nonholo-nomic tracked mobile robots, and illustrate the validity of the proposed control algorithm.

Development of Precise-temperature-controlled Cooling Apparatus for Medical Application by Using Peltier Effect

This paper describes precise temperature controlled cooling apparatuses for medical application. A Peltier cryoprobe for dermis treatment and flexible cryoprobe for cryosurgery for deep region of human body were developed by utilizing the Peltier effect. The evaluation experiment of the Peltier cryoprobe was conducted. The proposed apparatus has enough performance to necrotize target diseased cells precisely. The proposed flexible cryoprobe is composed of a flexible resin tube enough to treat the deeper parts of the human body with a catheter. A Peltier element is attached at the top of the probe for active heat-transfer control of the cooling tip. The cooling experiments are carried out and the performance of the cryoprobe is evaluated. The achieved minimum temperature at the tip is -43degC.

Precise Control of Frozen Region During Cryosurgery Utilizing Peltier Effect

In cryosurgery, it is necessary to control heat transfer precisely and actively in order to necrotize diseased part effectively and to avoid freezing healthy tissues. In order to control heat transfer, the cryoprobe utilizing peltier module was developed. This cryoprobe makes it possible to control cooling and heating rate actively and precisely due to peltier effect. Therefore, it is convenient to control the size of cell-destroyed area. In order to confirm cooling performance of the cryoprobe, gelatin cooling experiment and animal experiment was conducted. From the results, it can be said that this cryoprobe has enough cooling performance to destroy undesirable cell and it can control cooling and heating rate actively. Numerical simulation which considers biological heat production, freezing of tissue and peltier effect at same time was developed in order to evaluate frozen region or necrotized area, which are difficult to be measured.Copyright