LOW-INVASIVE HEATING AND TEMPERATURE

MEASUREMENT METHOD FOR HYPERTHERMIA TREATMENT

USING THE METAL COATED FERROMAGNETIC IMPLANT

WITH LOW CURIE TEMPERATURE

Kazutaka Mitobe and Noboru Yoshimura

Faculty of Engineering and Resource Science, Akita University, 1-1 Tegatagakuencho, Akita, Japan

Keywords: Hyperthermia, Cancer, Low-invasive, Induction Heating, Wireless Temperature Measurement System.

Abstract: Hyperthermia has been used for many years to treat various types of malignant tumor because tumor cells

are more sensitive to temperature in the range of 42-45°C than are normal tissue cells. In this study, we aim

to develop the local heating method and monitoring method for hyperthermia using the Ferromagnetic

Implant with Low Curie Temperature (FILCT) under high frequency magnetic field. The heat generation

inefficiency of FILCT causes a barrier in order to use this method as a bedside tool. In this research work,

we coated the FILCT with a metal material in order to improve the heat generation efficiency. The magnetic

permeability of FILCT decreased around the Curie temperature; therefore we can use FILCT as a thermal

probe by measuring of the changing vector of the magnetic flux at the outside of human body

noninvasively. In this paper, we describe about the experimental setup and in vitro experimental results.

1 INTRODUCTION

Hyperthermia has been used for many years to treat

various types of malignant tumor because tumor

cells are more sensitive to temperature in the range

of 42-45°C than are normal tissue cells (Cavaliere,

R., 1967 and Overgaard, K., 1972). There are a lot

of heating methods for hyperthermia. The most

commonly used method of heating in clinical

settings is capacitive heating using a radiofrequency

electrical field (Ishida, T., 1980, Abe, M., 1986 and

Hiraoka, M., 1994). The great advantage of

capacitive heating is that it is non-invasive.

However, this method can cause excessive heating

of the fat layer and is not suitable for site-specific

hyperthermia because it is difficult to selectively

heat only the local tumor region to the intended

temperature without also damaging normal tissue.

Moreover, this method needs an invasive

thermometer to measure the temperature of tumor

region. To overcome the disadvantages of capacitive

heating for the treatment of tumors, attempts have

been made to use inductive heating with magnetic

implants (Jordan, A., 1993 and Shinkai, M., 1996).

In 1982, Matsuki et al. developed a soft-heating

method using the ferrite implant with low Curie

point (Masaki, H., 1982). The merit of the soft-

heating method is that it needn’t measure the

temperature as for the heat generation is

automatically stopped up to Curie point of the

implant. We previously described a system in which

hyperthermia was induced using ‘ferromagnetic

implant with low Curie temperature (FILCT)’ low

enough to mediate automatic temperature control,

and demonstrated its antitumor effect in a mouse

melanoma model (Saito, H., 2008 and Ito, A. 2009).

However, the improvement of the heating efficiency

was necessary because much energy had been

required to heat the target tumor.

In order to solve this problem, we have mixed

the high conductivity metal material with FILCT.

At the same time, we have used FILCT as a probe of

thermometer. Thus a less invasive heating and

temperature measurement system was developed

based on this idea. A key advantage of this system is

that it can distinguish whether the target temperature

has reached the Curie temperature or not by non

contact method. On the other hand, the infrared (IR)

thermography, which is the most popular noncontact

thermometer, can measure the skin temperature but

not the internal body temperature. We have

developed the experimental setup for the less

341

Mitobe K. and Yoshimura N..

LOW-INVASIVE HEATING AND TEMPERATURE MEASUREMENT METHOD FOR HYPERTHERMIA TREATMENT USING THE METAL COATED

FERROMAGNETIC IMPLANT WITH LOW CURIE TEMPERATURE.

DOI: 10.5220/0003152803410344

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2011), pages 341-344

ISBN: 978-989-8425-37-9

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

invasive thermometry (Mitobe, K., 2008). In this

paper, we have assessed the appropriateness of this

system by the experiment of temperature

dependence and heating efficiency using the ‘Au

coated FILCT’.

2 EXPERIMENTAL SETUP

Ferromagnetic material with high magnetic

permeability attracts magnetic flux. If the

temperature of ferromagnetic material increases over

Curie temperature, then the magnetic permeability

decreases immediately. As a result, the material can

not attract magnetic flux. Figure 1 shows

fundamental concept of non-invasive thermometry.

The temperature of FILCT can be measured

noninvasively by the shift of vector of magnetic flux.

The Curie temperature of FILCT has been set at

43°C which is the target temperature in order to

reduce the tumor cell.

Figure 2 shows the micrograph of FILCT' and 'Au

coated FILCT’. FILCT was coated by Au in order to

enhance heat divergence efficiency. Au coated

FILCT was made using electroless gold plating

technique without underlaying harmful metal such

as Ni.

Figure 3 shows the block diagram of the

experimental setup of this experiment. Magnetic flux

was generated by the drive coil of 3 turns (External

diameter of the drive coil was 80mm, internal

diameter was 70mm). The frequency of the AC

current for the drive coil was 190 kHz. AC current

(500A) was generated by the power amplifier

(Hotshot, AMERITHERM Inc.). The shift of

vertical component of magnetic flux was measured

as variation of the induced voltage of the pickup coil.

The voltage of the pickup coil located orthogonally

in the drive coil was measured as the synchronous

signal of the voltage of the search coil by the lock-in

amplifier (7265 DSP Lock-in amplifier, Signal

Recovery). The number of turns, resistance, external

and internal diameter of the pickup coil was 10 turns,

10Ω, 17mm and 10mm respectively. The

temperature of FILCT was measured by an optical

fiber thermometer (FL-2000, Anritsu-meter). In this

experiment, we used Au coated FILCT (particle

diameter was 40µm-150µm, total mass of powder

was 1.0g) with 500µl of deionized water. The

distance between the upper surface of the drive coil

and a test tube of FILCT was 30mm, and the density

of magnetic flux at the position of FILCT was

24.3mT.

Figure 1: The fundamental concept of less invasive

thermometry.

(a) FILCT (b) Au coated FILCT

Figure 2: Micrograph of a particle of the ferromagnetic

implant with low Curie temperature.

Power Unit

HOT SHOT

LOCK-IN AMPLIFIER

Pickup Coil

Seach Coil

FILCT

Drive Coil

Figure 3: Block diagram of the experimental setup of the

less-invasive heating and thermometry.

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

FILC T Sputter-deposited

FILC T

A u c o a t e d F IL C T

R a te o f tem perature increase [℃/s]

Figure 4: Rate of temperature increase.

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3 RESULTS AND DISCUSSIONS

Figure 4 shows the rate of temperature increase of

each implant. Applied density of magnetic flux was

7.85mT, the frequency was 190 kHz. The thickness

of ‘Au coated FILCT’ was around 0.7µm. The rate

of temperature increase of ‘Au coated FILCT’ was

decuple compared with original FILCT.

We repeated induction heating over 50 times in

order to evaluate the endurance of Au coating.

Figure 5 shows the temperature rise curve of ‘Au

coated FILCT’. Here, horizontal axis shows time

and vertical axis shows the average temperature of

50 times cycle test. As a result, the heat divergence

profile was constant. We did not find any change in

surface of Au coat FILCT such as a delamination or

a crack after cycle tests by microscopic observation.

Figure 6 shows the change of the temperature of

Au coated FILCT and the magnetic flux density at

the pickup coil. Vertical axis shows the temperature

of FILCT and the magnetic flux density at the

pickup coil. The self-heating type FILCT produced

heat of over 43 ˚C that was effective in the treatment

temperature of malignancy. The temperature of

FILCT rose to 43 ˚C within 30s. Rate of temperature

increase changed around the Curie temperature. The

magnetic flux density at the pickup coil was

decreased in contradiction to the rising of

temperature.

Figure 7 shows the relationship between the

temperature of FILCT and the voltage of pickup coil.

This graph was made from the data of figure 6 that

was the result of cyclic test of heating. Here,

horizontal axis shows the temperature and vertical

axis shows the voltage of pickup coil. The profile of

the voltage was almost same on each trial, and the

voltage was decreased to 6mV. At the same time, the

bias of voltage caused by the difference of position

of FILCT appeared.

This approach can pave the way to heating and

temperature measurements of tumor with no pain

after injecting of FILCT to the tumor. However,

long time measurements may be a burden to the

subject persons as the body movements are restricted

to minimize the noise for this method.

4 CONCLUSIONS

In this paper, we have described the concept for

using ‘ferromagnetic implant with low Curie

temperature (FILCT)’ as a probe for temperature. A

key advantage of this system is that it can

distinguish noninvasively whether the target

temperature has reached the Curie temperature or

not. Less invasive heating and temperature

measurement system was evaluated using powder

type of Au coated FILCT. As a result, it has become

clear that we can heat up to 50mm of depth distance

under thermal control. Furthermore, it is clear that

we can use Au coated FILCT which have high

heating efficiency for induction of heating. These

results contribute to the less invasive heating and

temperature measurement for a lot of types of

hyperthermia.

0 100 200 300 400 500 600

Time [s]

Temperature [

℃

]

Figure 5: Temperature rise curve of 'Au coated FILCT'.

(50 times cycle tests).

25.0

30.0

35.0

40.0

45.0

50.0

55.0

0 20 40 60 80 100 120

Time [s]

Temperature [

℃

]

119

120

121

122

123

124

125

126

127

128

129

130

Magnetic flux density a

Pickup Coil [μT]

Tem perature [℃]

M agnetic flux density at P ickup C oil [u T ]

Figure 6: Change of the temperature of Au-coated FILCT

and the voltage of pickup coil.

120

122

124

126

128

130

30.035.0 40.0 45.0 50.0

Tem perature [℃]

M agnetic flux density at

Pickup C oil [μ T ]

Figure 7: Relationship between temperature of FILCT an

the voltage of the pickup coil.

LOW-INVASIVE HEATING AND TEMPERATURE MEASUREMENT METHOD FOR HYPERTHERMIA

TREATMENT USING THE METAL COATED FERROMAGNETIC IMPLANT WITH LOW CURIE TEMPERATURE

343

ACKNOWLEDGEMENTS

This work was supported in part by the Grant-in-Aid

for Scientific Research under Grant 21500438. We

express our thanks to Dr. Hajime Saito, an assistant

professor of medical school of Akita University. We

show our appreciation to Mr. Wu Yanfeng and Mr.

Yu Sugawara, graduated students of our laboratory.

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