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.

Heating properties of a new hyperthermia system for deep tumors without contact.

In this paper, heating properties of the proposed hyperthermia system for non-invasive treatment of deep tumors are discussed. Our heating system is composed of a large size resonant cavity applicator. In this heating method, a human body is placed between the two inner electrodes. It is heated by electromagnetic fields stimulated in the cavity without contact between the surface of the human body and the applicator. First, we presented the experimental results of heating a cylindrical agar phantom and a cylindrical fat-agar phantom using the proposed system. From the thermal images of the heated phantoms, the center of the agar was locally heated to maximum temperature. Second, we presented the experimental results of heating a mini pig. In the heating experiment, temperature measurements were performed by using fiber-optical thermometers inserted in four locations inside the mini pig. From the results, the deepest region of the liver was heated to the highest temperature 43.3 °C.

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 coaxial needle applicator made of SMA for hyperthermia treatments.

This paper describes heating properties of the developed coaxial needle applicator made of a shape memory alloy (SMA) for brain tumor hyperthermia treatments to avoid undesirable hotspots. We estimated the temperature distribution inside an agar phantom by the finite element method (FEM) and heated the agar phantom with the developed needle applicator.

Basic study of brain injury mechanism.

The purpose of this study is to discuss the mechanism of brain injury experimentally paying attention to the pressure changes on the surface of a brain agar phantom generated by a cavitation.

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.

Heating properties of the re-entrant type cavity applicator for brain tumor with several resonant frequencies.

We have proposed the re-entrant resonant cavity applicator system for non-invasive brain tumor hyperthermia treatment. In this method, a human head is placed in the gap of the inner electrodes. A brain tumor is heated with the electromagnetic field stimulated in the cavity without contact between the human head and the applicator. We have already presented the effectiveness of the heating properties of this system with cylinder-type agar phantoms and by computer simulations. This paper discusses the heating properties of the developed system with the human head-type agar phantom for brain tumor hyperthermia treatment. First, in order to heat deep brain tumors, we tried to heat the human head-type agar phantom by using several electromagnetic field patterns of the resonant frequency. We found that the temperature distributions can be controlled inside the agar phantom by changing the resonant frequencies. Second, to heat local and deep areas of the agar phantom, we tried to achieve heating using the two different resonant frequencies. We found distinct heating properties by changing the electromagnetic field patterns of resonant frequencies. From these results, it was found that our developed heating system can be applied to hyperthermia treatments of deep-seated brain tumors. Further, by changing resonant frequency, treatment can very correspond to the size and the position of a tumor.

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.

Heating properties of re-entrant resonant cavity applicator for brain tumor with simple head model.

We have already confirmed the effectiveness of the re-entrant resonant cavity applicator system with non-invasive experiments of heating cylindrical agar phantoms and computer simulations. This paper discusses the heating properties of the developed heating system with a human head model made of agar for brain tumor hyperthermia treatment. First, we present the results of heating a uniform agar head model with the developed heating system. In the experiments, the temperature rise at the center of the agar was about 8 degrees C, it was found that the center of the agar is heated to maximum temperature non-invasively. Second, we present the results of heating a non-uniform agar head model having an oral cavity and a nasal cavity. We found that the center of the agar can be heated to maximum temperature as well as uniform agar head model. From these results, it is confirmed that the possibility of effective hyperthermia for various types of deep-seated 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. Here, comparing frequency and pressure changes, we discussed the basic mechanism of brain injury analytically. First, a three-dimensional FEM model for impact analysis was presented. The high-pressure changes generated in the acrylic container at the time of impact were transmitted through this container, and the positive maximum pressure change was caused at the contrecoup side. Second, the results of the frequency analysis of pressure changes by a FFT were presented. We found spectrums in some frequency bands, which seemed to be the occurrence of the brain injury. From these results, it was found that the computer simulation methods were useful to predict the occurrence mechanism of contrecoup injury.

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.

Improvement of needle type applicator made of shape memory alloy.

This paper discusses radio frequency (RF) interstitial hyperthermia for brain tumors with a developed needle type applicator made of a shape memory alloy (SMA). The problem with the heating method of interstitial hyperthermia is the small heating area. So, we proposed a new heating method using a needle type electrode made of SMA which consists of nickel (Ni), copper (Cu) and titanium (Ti) for expanding the heating area. Here, we proposed the heating method that the leading end of needle type electrode was divided into four parts and the leading end spreads in four directions with a temperature rise. First, the proposed RF interstitial hyperthermia system with the SMA needle was presented. Second, the results obtained by the experimental heating of the agar phantom by using the developed SMA needle type applicator were presented. Third, comparing experimental results, we discussed the heating properties of the developed system. Finally, from these results, it is confirmed that the developed needle type applicator made of SMA is useful for wide heating by invasive hyperthermia.

Heating properties of developed needle type applicator made of shape memory alloy.

This paper discusses radio frequency (RF) interstitial hyperthermia for a brain tumor with a needle type applicator made of a shape memory alloy (SMA). In this method, it is necessary to make appropriate thermal distribution to the region of the brain tumor. However, it is not easy to predict the thermal distribution during the heating. We estimated the temperature distribution inside an agar phantom by the finite element method (FEM), and heated the agar phantom with the developed needle type applicator. Here, first, the developed RF interstitial hyperthermia system with the SMA needle was presented. Second, the results obtained by the computer simulation and the experimental heating results of the agar phantom by using the developed SMA needle type applicator were presented. Comparing computer simulation results and experimental results, we discussed the heating properties of the developed system. Finally, from these results, it is confirmed that the developed needle type applicator made of SMA is useful for wide heating of invasive hyperthermia.

Finite element analysis of the re-entrant type resonant cavity applicator for brain tumor hyperthermia.

In this paper, we have proposed a new heating method in which high frequency electric fields in a re-entrant type resonant cavity are used for the heating of deeply seated tumors. In this method, a human head is placed between the gap of the inner re-entrant cylinders, and is heated with electromagnetic fields stimulated in the cavity without contact between the surface of the human head and the applicator. Here, we proposed a new method to control the heating area. In this method, the resonant frequency inside the cavity was changed, then we use the TM010-like mode and the TM012-like mode from various types of the resonant frequency. First, the computer simulation results of electric and magnetic field patterns are presented. Second, a comparison of the heating properties of TM010-like mode and TM012-like mode are discussed. The heating area of the center of agar phantom is more concentrated by using TM012-like mode than that of using TM010-like mode. From these results, it is confirmed that the proposed method can be controlled to heat the various sizes of deep tumors.

Heating properties of re-entrant resonant applicator for brain tumor by electromagnetic heating modes.

This paper discusses a new method to control the heating area of a re-entrant resonant cavity applicator for brain tumor hyperthermia treatment non-invasively. We have already discussed about the effectiveness of a developed system with experiments of heating an agar phantom and computer simulations. Here, in order to heat a deep brain tumor, we propose the heating method of using several electromagnetic heating modes which are transverse magnetic (TM) modes. In this method, TM010-like and TM012-like modes obtained by selecting resonant frequencies can be used to heat the deep brain tumors. To control the heating area of the modes the agar phantom is used in the heating experiments by the developed system. From these results, we found that the heating area of the agar phantom by using TM012-like mode is about 50% of the heating area of TM010-like mode. It is found that the proposed heating system can be applicable to the hyperthermia treatment of brain tumors corresponding to the size and the position where it occurred.

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.

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.

Experimental heating properties of re-entrant type resonant cavity applicator for deep tumor hyperthermia.

This paper discusses the heating properties of a new type hyperthermia system composed of a re-entrant type resonant cavity applicator for a deep tumor of the abdominal region. In this heating method, a human body is placed between the two inner electrodes, and is heated with electromagnetic fields stimulated in the cavity without contact between the surface of the human body and the applicator. First, the experimental heating results of an agar-muscle equivalent phantom were presented. Second, we performed an experiment with a lard-agar phantom. The center region of the agar phantom could be heated selectively without generating hot spots in the lard layers. From these results, it was found that our newly developed heating method is useful for a deep-seated tumor hyperthermia treatment.

Design and construction of resonant cavity applicator for brain tumor hyperthermia treatment without contact.

A re-entrant type resonant cavity applicator for brain tumor hyperthermia treatment is presented. In this method, a human brain is placed between the gap of the inner re-entrant cylinders without contact. This cavity has a window for insertion of the human head. Here, first, to design and construct a resonant cavity applicator, the results of the temperature distribution inside an agar phantom and electromagnetic field leaked from the attached window to the environment by the computer simulation were presented. Second, The developed resonant cavity and inner electrode, which were made of an aluminum alloy, were presented. Third, the experimental heating result of the agar phantom was presented. In the experiment, the center region of the agar phantom is heated to 42 degrees C. The leaked electric field strength at the position of 10 cm away from the center of the window was less than that of 10% of the center of the agar phantom. It was found that the developed resonant cavity applicator was applicable to both deep and regional brain hyperthermia treatment.