Mitsunori Kubo

Basic study of brain injury mechanism caused by cavitation

The purpose of this study is to discuss the mechanism of brain injury experimentally, with respect to the pressure changes on the surface of a brain agar phantom by cavitation. First, an experimental system to perform an impact experiment is presented. We present some images taken by a high-speed camera of the behavior of a simple physical head model with and without the brain agar phantom during impact. From the photographs of the high-speed camera, we can confirm that cavitation bubbles occur at the contrecoup side, irrespective of the usage of the brain agar phantom. Second, two experimental systems to perform impact and strike experiments are presented. The pressure changes on the surface of the brain agar phantom at contrecoup side were measured by two kinds of experiments and impact velocities. Frequency analysis of the measured pressure changes was conducted by FFT software. From these results, we found that the collapse of cavitation bubbles at the contrecoup side can strongly affect the characteristics of pressure changes on the surface of the brain agar phantom.

Finite element analysis and experimental study on mechanism of brain injury using brain model.

The aim of this study is to discuss the occurrence mechanism of the brain injury analytically and experimentally. In this paper, first, an experimental system to do an impact experiment was presented. The pressure changes inside a brain agar phantom were measured. Second, a three-dimensional FEM model of the impact experiment was constructed. From the results of the fundamental analysis, the transmitted pressure inside the brain agar phantom could be presented. The comparison of the computer simulation and experimental results showed that the negative pressure values, same as the positive pressure occurred in the coup side region of the agar, also appeared in the contrecoup side region of the agar

Heating properties of non-invasive hyperthermia treatment for abdominal deep tumors by 3-D FEM

This paper discusses the heating properties of a new type of hyperthermia system composed of a re-entrant type resonant cavity applicator for deep tumors of the abdominal region. In this method, a human body is placed in the gap of two inner electrodes and is non-invasively heated with electromagnetic fields stimulated in the cavity. Here, we calculated temperature distributions of a simple human abdominal phantom model that we constructed to examine the heating properties of the developed hyperthermia system. First, the proposed heating method and a simple abdominal model to calculate the temperature distribution are presented. Second, the computer simulation results of temperature distribution by 3-D FEM are presented. From these results, it was found that the proposed simple human abdominal phantom model composed of muscle, fat and lung was useful to test the heating properties of our heating method. Our heating method was also effective to non-invasively heat abdominal deep tumors.

Finite element analysis of the needle type applicator made of shape memory alloy

In this paper, we propose a new heating method in which we use shape memory alloy (SMA) in a needle type applicator for brain tumor hyperthermia. In order to expand the heating area of a needle type applicator and to control the heating pattern for various sizes of tumors, some kinds of SMA needle type applicators were developed. To apply the proposed heating method safely to clinical hyperthermia, it is necessary to make appropriate thermal distribution to the region of the brain tumor. However, it is not easy to predict the three dimensional temperature distribution during the human brain tumor hyperthermia. Therefore, we estimated the temperature distribution inside the agar phantom by the finite element method (FEM). Here, first, the computer simulation results of temperature distributions under the different heating times are discussed. Second, a comparison of the heating properties obtained by using the needle type electrodes made of different shaped SMA is discussed. From these results, it is confirmed that the proposed heating method can expand the heating area and control the heating pattern for the various sizes of brain tumors.

3-D Finite Element Analysis and Experimental Study on Brain Injury Mechanism

The purpose of this paper is to discuss the basic study of mechanism of brain injury analytically and experimentally, in respect to the frequency analysis of the pressure changes. First, a three-dimensional FEM model for impact analysis was presented. The pressure changes inside a brain agar phantom and its frequency analysis were calculated. Second, an experimental system to perform an impact experiment was presented. In the impact experiments, the pressure changes inside a brain agar phantom after impact were measured. The comparison of the computer simulation and the experimental results of the impacts showed that the negative pressure, which seemed to cause the contrecoup injury at the contrecoup side of a brain, also appeared in the contrecoup side of the brain agar phantom. Finally the results of the frequency analysis of pressure changes by FFT were presented. From the results of computer simulations and impact experiments, we found similar spectrums in some frequency bands, which seemed to be the occurrence of the brain injury.

SAR analysis of the improved resonant cavity applicator with electrical shield and water bolus for deep tumors by a 3-D FEM

This paper discusses the improvements of the re-entrant resonant cavity applicator, such as an electromagnetic shield and a water bolus for concentrating heating energy on deep tumors in an abdominal region of the human body. From our previous study, it was found that the proposed heating system using the resonant cavity applicator, was effective for heating brain tumors and also for heating other small objects. However, when heating the abdomen with the developed applicator, undesirable areas such as the neck, arm, hip and breast were heated. Therefore, we have improved the resonant cavity applicator to overcome these problems. First, a cylindrical shield made of an aluminum alloy was installed inside the cavity. It was designed to protect non-tumorous areas from concentrated electromagnetic fields. Second, in order to concentrate heating energy on deep tumors inside the human body, a water bolus was installed around the body. Third, the length of the lower inner electrode was changed to control the heating area. In this study, to evaluate the effectiveness of the proposed methods, specific absorption rate (SAR) distributions were calculated by FEM with the 3-D anatomical human body model reconstructed from MRI images. From these results, it was confirmed that the improved heating system was effective to non-invasively heat abdominal deep tumors.

A new heating method with dielectric bolus using resonant cavity applicator for brain tumors

In this paper, we discuss a new method of controlling heating location in the proposed resonant cavity applicator. A dielectric bolus was used to non-invasively treat brain tumors. We have already confirmed that our heating system using resonant cavity is useful to non-invasively heat brain tumors. In order to heat tumors occurring at various locations, it is necessary to control the heating area with our heating system. First, we presented the proposed heating method and a phantom model to calculate temperature distributions. The results of temperature distributions were discussed. Second, a 3-D human head model constructed from 2-D MRI images was presented. The results of specific absorption rate distributions were discussed. From these results, it was found that the proposed heating method was useful to non-invasively treat brain tumors.

SAR analysis of a re-entrant resonant cavity applicator for brain tumor hyperthermia treatment with a 3-D anatomical human head model

A re-entrant resonant cavity applicator system for non-invasive brain tumor hyperthermia treatments was presented. We have already confirmed the effectiveness of the heating properties of this heating system with cylindrical agar phantoms and with computer simulations.

Heating properties of the needle type applicator made of shape memory alloy by 3-D anatomical human head model

Since the human brain is protected by the skull, it is not easy to non-invasively heat deep brain tumors with electromagnetic energy for hyperthermia treatments. Generally, needle type applicators were used in clinical practice to heat brain tumors. To expand the heating area of needle type applicators, we have developed a new type of needle made of a shape memory alloy (SMA). In this paper, heating properties of the proposed SMA needle type applicator were discussed. Here, in order to apply the SMA needle type applicator clinically. First, we constructed an anatomical 3-D FEM model from MRI and X-ray CT images using 3D-CAD software. Second, we estimated electric and temperature distributions to confirm the SMA needle type applicator using the FEM soft were JMAG-Studio. From these results, it was confirmed that the proposed method can expand the heating area and control the heating of various sizes of brain tumors.

3-D finite element analysis on brain injury mechanism

The purpose of this study is to discuss the mechanism of brain injury analytically by a cavitation phenomenon. Cavitation damage is assumed to be one of the causes brain injury. Performing the computer simulation of brain injury, it is not easy to incorporate the term of a cavitation occurrence in a governing equation. Therefore, we predict the cavitation occurrence from the results of stress, pressure, and displacement of the analytical model by FEM.