bio electrical impedance analysis system for visceral fat … · 2020. 7. 3. · visceral fat area...
TRANSCRIPT
１
Bio electrical impedance analysis system
for visceral fat measurement
Kwang soo , Kim
Department of Medical Science
The Graduate School, Yonsei University
２
Bio electrical impedance analysis system
for visceral fat measurement
Kwang soo , Kim
Department of Medical Science
The Graduate School, Yonsei University
３
Bio electrical impedance analysis system
for visceral fat measurement
Directed by Professor Sun K. Yoo.
The Master's Thesis
submitted to the Department of Medical Science,
the Graduate School of Yonsei University
in partial fulfillment of the requirements for the degree
of Master of Medical Science
Kwang soo, Kim
December 2009
４
This certifies that the Master's Thesis
of Kwangsoo, Kim is
approved.
------------------------------------
Thesis Supervisor: Sun K. Yoo
------------------------------------ Thesis Committee Member: Sun Ha, Jee
------------------------------------
Thesis Committee Member: Bong Soo, Cha
The Graduate School
Yonsei University
December 2009
５
ACKNOWLEDGEMENTS
내가 여호와를 항상 송축함이여 그를 송축함이 내 입에 계속하리로다 (시 34편)
한 분야의 전문인이 되려면 1만시간 이상을 투자하라는 말이 있습니다. 학문의
상아탑인 대학원에 들어와 좋은 결실을 맺기 위해 노력하던 여러 날을 떠올려봅니
다. 쉽지 않던 과정이 있었기에 지금은 돌아보며 뿌듯함을 느낄 수 있는 것 같습니
다.
본 논문이 이루어지기까지 여러 모로 부족한 저를 많은 배려와 가르침으로 이끌
어주신 유선국 지도 교수님께 깊은 감사를 드립니다. 그리고 저의 논문 지도를 위
해 바쁜 시간을 내어 좋은 코멘트를 해주신 지선하 교수님, 차봉수 교수님께도 감
사의 말씀을 전합니다. 또한 곁에서 항상 마음 써 주시고 가르침을 보여주신 김남
현 교수님, 김덕원 교수님, 서활 교수님, 박종철 교수님, 이병채 교수님께도 감사
드립니다.
연구실 생활을 하면서 늘 앞장서고 도움이 되는 사람이 되고 싶었는데, 지금 생
각해보면 도움을 주기보다는 도움을 많이 받았던 것 같습니다. 2년 생활의 거의 모
든 시간을 함께했던 연구실 선후배님들께 깊은 감사의 마음을 전합니다. 인자하신
석명형, 지금은 교수가 되신 동근형, 늘 넉넉함을 보여주신 나지영 선생님, 멋진 모
범되신 순만형, 여러모로 잘 챙겨주시고 힘이 되어 주신 충기형, 연구실 친목의 대
장이신 도윤형, 한 팀으로 함께 수고하고 나 때문에 고생 많았던 섬세한 정채와 미
소 가득 미희누나, 멋진 선배 윤재형, 회식 문화의 새로운 장을 열어주신 서민교
선생님, 2년을 함께 보내며 동기로 호흡한 늘 편안한 동지 수호와 기도모임을 함께
하고 많은 힘과 위로가 된 성혜누나, 함께 졸업하지 못해 아쉬움이 남는 현택이와
유쾌한 김해 미스 은정이, 매너남 흑형 우진형과 착한 말괄량이 동생 주현이, 성실
６
하고 납땜 잘하는 안세와 분위기 있는 보규, 여운 남기는 강일이와 지금은 졸업한
선배들인 든든한 영재형과 늘 편한 친구인 한규와 용귀, 조용한 상용이형과 재주
많은 도성이형과 인호형, 동규형 이 모든 분들께 감사의 마음을 전하고 싶습니다.
언제나 편안하고, 즐거움을 주었던 오랜 친구인 영준이와 영준이를 통해 새롭게
알게 된 좋은 친구들 영욱, 정수형, 정은, 영실, 혜진이와 고등학교 친구들인 민수,
석훈, 형규, 상현. 내 인생 동지 은수, 대휘, 동훈 너희들 덕분에 힘든 내 인생은
참 풍요롭고 즐겁단다. 이들과 이곳에 다 적지 못한 대학 선후배님께 감사의 말씀
을 전합니다. 특별히 끊임없는 열정으로 좋은 영향을 주신 박수경 선생님과 연구실
생활을 하는 동안 변함없는 따뜻한 배려와 사랑으로 함께해 준 여자친구 보혜와
보혜 부모님께 감사를 드립니다.
마지막으로 언제나 저를 믿어주시고 든든한 후원자가 되어주신 부모님께 감사
드립니다. 매일 아침 저를 위해 해주신 기도들을 전 평생 잊지 못할 거에요..
부족한 동생을 늘 자신처럼 아껴준 형에게도 깊은 감사의 마음을 전합니다.
마지막은 새로운 시작이라는 말을 기억합니다. 고마우신 분들의 가르침을 잊지
않고 잘 새기며 늘 도전하는 마음과 정신으로 멋지게 살아가도록 하겠습니다.
감사합니다.
2009년 12월
김 광수 올림
７
<TABLE OF CONTENTS>
ABSTRACT………………………………………………………… 1
I. INTRODUCTION………………………………………………………… 2
II. MATERIALS AND METHODS………………………………………… 4
1. Theoretical Background ……………………………………… 4
A. Visceral adiposity and metabolic syndrome ………………… 4
B. Visceral fat measurement by computed tomography …………… 5
C. Visceral fat measurement by Bio electrical impedance analysis … 8
(A) Bio electrical analysis ……………………………………… 8
(B) Electrical body model analysis …………………………… 9
ⓐ Series-equivalent model…………………………… 10
ⓑ Parallel-equivalent model…………………………… 11
(C) Electrical properties of tissues and cells ……………… 12
D. Measurement conditions…………………………………… 14
E. Finite element method……………………………………… 14
2. H/W description of the visceral fat measurement ……………… 16
A. Specification of the system…………………………………… 16
B. Digital system………………………………………………… 17
C. Analog system………………………………………………… 19
D. Evaluation of the H/W system……………………………… 21
3. Abdomen modeling and FEM simulation……………………… 23
８
III. RESULTS……………………………………………………………… 29
1. Various electrode configurations ……………………………… 29
A. Electrodes with 1/16 waist ratio……………………………… 29
B. Electrodes with fixed distance………………………………… 31
C. Electrodes with adjacent method …………………………… 32
2. Various frequencies configurations…………………………… 36
IV. DISCUSSION………………………………………………………… 39
V. CONCLUSION………………………………………………………… 40
REFERENCES…………………………………………………………… 41
ABSTRACT (IN KOREAN) …………………………………………… 44
９
LIST OF FIGURES
Figure 1. Abdomen fat CT at L 4-5 · · · · · · · · · · · · · · · · · · 7
Figure 2. Electrical body model analysis · · · · · · · · · · · · · · · · 9
Figure 3. Digital system diagram · · · · · · · · · · · · · · · · · · · 17
Figure 4. Waveform of AD9833 · · · · · · · · · · · · · · · · · · · · 18
Figure 5. Analog system diagram · · · · · · · · · · · · · · · · · · · 19
Figure 6. Peak detector output · · · · · · · · · · · · · · · · · · · · · 20
Figure 7. Impedance test results · · · · · · · · · · · · · · · · · · · · 21
Figure 8. CT, Abdomen level (Lumbar 4-5) · · · · · · · · · · · · 23
Figure 9. Abdomen model (COMSOL, Lumbar 4-5) · · · · · · 24
Figure 10. Abdomen region dividing by MIMICS · · · · · · · · 24
Figure 11. Abdomen model 1, 2 · · · · · · · · · · · · · · · · · · · 25
Figure 12. Various electrode configurations · · · · · · · · · · · 27
Figure 13. Results of electrodes with 1/16 waist ratio arrangement
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 30-31
Figure 14. Results of fixed distance electrodes arrangement · · · 33
Figure 15. Model 1 with adjacent electrodes arrangement · · · 34
Figure 16. Model 2 with adjacent electrode arrangement · · · · 35
Figure 17. Model 1 with frequency variation · · · · · · · · · · · 37
Figure 18. Model 2 with frequency variation · · · · · · · · · · · 38
１０
LIST OF TABLES
Table 1. Specification of the system · · · · · · · · · · · · · · · · · · · · 16
Table 2. Results of bio electrical impedance analyzer · · · · · · · · 22
Table 3. Each properties at 100 kHz and HU values · · · · · · · · 25
Table 4. Normal and manipulated model proportion ratio · · · · 26
Table 5. Permittivity and conductivity changes with frequencies · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 28
Table 6. Measured voltage at each point A, B, C (V) · · · · · · · 29
Table 7. Measured voltage with fixed distance (V) · · · · · · · · 31
Table 8. Measured voltage with adjacent method (V) · · · · · · 32
Table 9. Measured voltage with frequency variation (V) · · · · · 36
１１
<ABSTRACT>
Bio electrical impedance analysis system
for visceral fat measurement
Kwang soo, Kim
Department of Medical Science
The Graduate School, Yonsei University
(Directed by Professor Sun K. Yoo)
Excessive amount of visceral fat is considered as a crucial indicator for the
metabolic syndrome. Visceral fat area (VFA) at the umbilicus level
measured by CT is adopted as the gold standard, but it has many limitations.
Recently, Application of bioelectrical impedance analysis (BIA) for
measuring VFA is widely used. By the way, the correlation between
impedance and VFA is highly dependent on the measurement conditions.
Therefore, we need to find appropriate measurement conditions and for
finding optimum conditions we introduce finite element method here.
In this study, we made two mesh abdomen models and manipulate its
conditions variously. And we also choose various different electrode
configurations with changes of frequency for evaluating its performance to
measure visceral fat with impedance. Our results indicated that electrode
arrangement with waist ratio is better performance than other electrode
arrangement. Current electrode on each flank side is better than on the front
and rear side. And frequency variation for measuring visceral and
subcutaneous fat separately seems incapable.
Our preliminary experiment results are presented.
----------------------------------------------------------------------------------------------------------
Key words : Metabolic syndrome, visceral fat, bioelectrical impedance analysis (BIA),
Measurement condition
１２
Bio electrical impedance analysis system
for visceral fat measurement
Kwang soo, Kim
Department of Medical Science
The Graduate School, Yonsei University
(Directed by Professor Sun K. Yoo )
I. INTRODUCTION
The metabolic syndrome has become one of the major public-health concerns
today. Metabolic syndrome is a combination of medical disorders that increase the
risk of developing cardiovascular diseases and diabetes. Many factors can be
considered as the cause of metabolic syndrome such as insulin resistance and hyper-
triglyceridaemic waist phenotype and visceral obesity etc.1-3
However, Central obesity, Excessive amount of visceral fat, is considered as a
crucial indicator for the metabolic syndrome. The International Diabetes Federation
(IDF) agree that central obesity is an early step in the aetiological cascade leading to
full metabolic syndrome.4-5
Visceral fat area (VFA) at the umbilicus level measured by CT is adopted as the
gold standard for measuring central obesity. Several studies revealed that visceral
fat areas from a single scan obtained at the level of the umbilicus (approximately
１３
level of L4 and L5) were highly correlated with the total visceral fat volume. When
umbilicus-level VFA exceeds 100 ㎠, the risk factor increases markedly. Likewise,
CT is the most trusted method for measuring visceral fat at present. However, it has
many limitations such as radiation exposure and high costs.8-9
Therefore, There has been a need for a simple and noninvasive method for
estimating VFA. The bioelectrical impedance analysis (BIA) method for estimating
VFA is simple, noninvasive and thus its potential in VFA assessment is being
studied widely. The BIA method flow a weak current through body and estimate
body composition by analyzing the impedance obtained. A current source supplies a
constant known current through the body and voltmeter measures the voltage of the
subject. Then we calculate impedance from the measured voltage.6, 7
By the way, the relation between impedance and VFA is highly dependent on the
measurement conditions. Several studies revealed that electrodes arrangement and
measurement posture can affect the impedance which including many tissue
characteristic and their electrical properties.13-15
Therefore, we need to find possible
measurement conditions and evaluate their performances for measuring visceral fat..
And for finding optimum measurement conditions, we introduce finite element
method (FEM) with ‘MIMICS’ and ‘COMSOL’ programs. With the FEM, we make
diverse models and do many experiments easily.
This paper is concerning for finding optimum condition when measuring visceral
fat area (VFA) by Bio electrical analysis (BIA) method. We also introduce device
description which we made in this experiment.
１４
II. MATERIALS AND METHODS
1. Theoretical Background
A. Visceral adiposity and metabolic syndrome
The metabolic syndrome is a constellation of interrelated risk factors of metabolic
origin that appear to directly promote the development of atherosclerotic cardio
vascular disease (ASCVD). Patients with the metabolic syndrome also are at
increased risk for developing type 2 diabetes mellitus. Over 23.7% of U.S.
population and fast increasing number of East Asian nation suffer from this
syndrome. The high prevalence of the metabolic syndrome has significant public
health implications.1-3
There have been many researches according to the relation of central obesity and
metabolic syndrome. Initial studies in this area regarded insulin resistance as a
primary factor of metabolic syndrome. And the definition of metabolic syndrome
was obscure. However, more recent investigations revealed that visceral adiposity is
a significant independent predictor of the metabolic syndrome (which includes
insulin sensitivity, impaired glucose tolerance, elevated blood pressure, and
dyslipidemia). And many studies revealed that visceral adiposity is independently
１５
associated with all of the metabolic syndrome criteria (insulin resistance, lower
HDL cholesterol, higher apolipoprotein B, and triglyceride levels, smaller LDL
particles, aortic stiffness, coronary artery calcification, and higher BP ), whereas
insulin sensitivity is independently associated with the criteria for HDL cholesterol,
TGs, and FPG. In contrast, subcutaneous fat area is independently associated with
only waist circumference after adjusting for visceral obesity area and insulin
sensitivity.4-5
Furthermore, a reduction in visceral adiposity by weight loss or surgical removal is
associated with increases in insulin sensitivity and HDL cholesterol and decrease in
TGs and BP. In this manner, visceral adiposity are regarded as crucial indicator of
metabolic syndrome.2-3
B. Visceral fat measurement by computed tomography
Visceral fat area can be obtained by computed tomography (CT). And this
method is adopted as the gold standard for measuring visceral fat area presently. On
CT scanner, -190 ~ -30 Hounsfield unit regarded as the region of fat tissue and the
area of fat tissue can be acquired by its program on CT. However, the position of CT
scan is different from each person on a basis of the umbilicus because of their
fatness difference.8
Therefore, Sjostrom suggests lumbar 4-5 for CT scans and Tohru Yoshizumi
reported the acquired visceral fat area has high correlation with the total visceral fat
volume with lumbar 4-5 CT scans.8-9
Some studies emphasizing visceral fat as a risk
１６
factor for metabolic disease have specified threshold values to identify subjects at
risk, e.g. a visceral fat area of ≥100 ㎠ has been used to identify some Japanese
individuals. However, there have been discrepancies between studies that have used
such values, and the differences are not completely explained by ethnic- or sex-
related confounders across investigations.6, 7
The visceral to subcutaneous adipose tissue area ratio (V:S ratio) describes the
relative accumulation of visceral and subcutaneous fat without defining absolute
quantity of fat in either depot. Use of the ratio value to integrate the size, and hence
the potential function of both adipose depots as correlates of systemic metabolism,
may mirror the actual human physiology more closely.2-3
Fujioka investigated that the group over 0.4 V:S ratio has significantly higher
cholesterol level, fasting plasma glucose level, fasting serum triglyceride level, and
serum total cholesterol level than in the group with a lower 0.4 (V:S ratio).2 These
relationships were also observed when examined in each sex separately and found
to be significantly higher in men than women group and older group than younger
group after adjustment for BMI and age by multiple regression analyses.
１７
Figure 1. Abdomen fat CT at L 4-5
This method is considered as a superior technique for the accurate assessment of
visceral fat measurement. However, it has its drawback such as radiation exposure
and high cost etc. Therefore, it is not appropriate for daily obesity care, fellow-up
observation, and observation for epidemiological study. Non-invasive, simple,
highly reliable method for visceral fat measurement needs to be developed.
１８
C. Visceral fat measurement by Bio electrical impedance
analysis
Bioelectrical impedance measurements are easy to perform (relative to other
measurements of body composition) and instruments are commercially available for
the purpose. For these reasons, bioelectrical impedance analysis (BIA) is gaining
acceptance outside the clinic and research laboratory.
(A) Bio electrical analysis
The electrical impedance of the body is measured by introducing a small
alternating electrical current into the body and measuring the potential difference
that results. The impedance magnitude Z is the ratio of the magnitude of the
potential difference to the magnitude of the current.11
With suitable equipment one can also measure the phase difference 0 between the
voltage and current. Alternating electrical current flows through the body by several
different physical mechanisms. Current flows through physiologic fluids by the
movement of ions. This movement is opposed by viscosity and other effects, which
can be modeled electrically as a resistance. In addition, the applied current will
charge cell membranes and other interfaces, which can be modeled electrically as
capacitors. Thus, the impedance of the human body (and of material in general) can
１９
be modeled by a combination of capacitive and resistive elements. A capacitance
and a resistance can be combined in two ways: in series or in parallel (Figure 2). In
either case, the components can be chosen to produce the same impedance of the
circuit; however, the component values will differ.10-12
(B) Electrical body model analysis
a) Series combination of model
b) Parallel combination of model
Figure 2. Electrical body model analysis
(combinations of a resistor and capacitor)
２０
ⓐ Series-equivalent model
The series-equivalent model shown in Figure 2 a) consists of a resistor Rs
(expressed in Ω ) in series with a capacitor CS(expressed in F). The magnitude of
the impedance of this circuit can be written
𝐙 = 𝐑𝐬𝟐 +
𝟏
(𝟐𝛑ƒ𝐂𝐬)𝟐
And the phase difference θ between voltage and current as
𝛉 = −𝐚𝐫𝐜𝐭𝐚𝐧 𝟏
𝟐𝛑ƒ𝐑𝐂𝐬
where f is the frequency (expressed in Hz). It is often useful to express the
impedance of this circuit in terms of a quantity Ζ∗, which is complex in the
mathematical sense:
𝐙∗ = 𝐑𝐬 − 𝐣
𝟐𝛑ƒ𝐂𝐬 = 𝐑𝐬 + 𝐣𝚾
where j is the square root of -1 and the asterisk denotes a complex quantity. In the
following expression, the quantity X is the reactance of the capacitor, expressed in
Ω ∶
２１
𝚾 = −𝟏
𝟐𝛑ƒ𝐂𝐬
The use of a complex number Zı to express the impedance is a mathematical
device. It allows the investigator to express both measured quantities (the
magnitude of the impedance and the phase difference between the voltage and
current) in terms of a single quantity, Ζ∗. Following the usual rules for handling
complex quantities, the impedance magnitude Z is the magnitude of the complex
quantity Ζ∗, and the phase angle 0 is the arctangent of the ratio of the imaginary to
real parts of Ζ∗.
ⓑ Parallel-equivalent model
For reasons discussed below, it is often more convenient to consider instead a
parallel circuit consisting of a resistor RP positioned in parallel with a capacitor
CP (Figure 2 b). The series-equivalent impedance of this circuit can be derived
simply by using the rules for addition of parallel circuit elements. In terms of the
parallel-equivalent resistance RP and capacitance CP , the series-equivalent
resistance RS and reactance X of the circuit can be obtained:
𝐑𝐬 =𝐑𝐏
𝟏 + (𝟐𝛑ƒ𝐂𝐏𝐑𝐏)𝟐
𝚾 =−𝟐𝛑ƒ𝐂𝐏𝐑𝐏
𝟐
𝟏 + (𝟐𝛑ƒ𝐂𝐏𝐑𝐏)𝟐
２２
The impedance magnitude Ζ of this circuit is
𝚭 = 𝟏
𝟏 𝐑𝐏𝟐 + (𝟐𝛑ƒ𝐂𝐬)𝟐
𝟏 𝟐
And the phase angle θ between voltage and current is
𝛉 = −𝐚𝐫𝐜𝐭𝐚𝐧(𝟐𝛑ƒ𝐂𝐏𝐑𝐏)
Whether one chooses to interpret impedance measurements in terms of parallel-
equivalent elements (RP and CP) or series equivalent elements (RS and CS) is a
matter of convenience. Most investigators report body impedance data in terms of
resistance and reactance, which implicitly refer to a series model as shown in Figure
1 A. By contrast, biophysical models of the electrical properties of tissue are more
naturally expressed with reference to a parallel model, as shown in Figure 2 b).
(C) Electrical properties of tissues and cells
The electrical properties of tissues have been studied for many years and a good
understanding exists of the relation between the bulk electrical properties of a tissue
and its structure. The elements of tissue structure that are most important include
cell size and volume fraction, membrane capacitance, and the conductivity of the
intracellular and extracellular media. The resistivity and permittivity of several
tissues at different frequencies (100 Hz - 1 GHz) used in body impedance studies
２３
are summarized in Table 5.17, 18
In the tissue-impedance literature there is considerable variability in the reported
data, with 2-fold variations in resistivity and 10-fold variations in permittivity often
present in data from the same tissue from the same species. In part this might reflect
normal biological variability, such as variability in tissue structure and (particularly
for adipose tissue) lipid content. Another potential source of variability is the
change in tissue properties after death. Many data in the literature were obtained
from excised tissues that were far removed from in vivo conditions. Twofold
increases in resistivity were reported in tissues within a few minutes after blood
flow ceased, apparently because of swelling of cells as the result of ischemia. In
short, some of the variability in the reported data might be important in BIA
analysis and other variability might simply reflect experimental artifacts.
These findings lead to several important conclusions. At frequencies used in
body impedance studies (which are typically in the range of 10 kHz to 1 MHz),
tissues are primarily resistive; their reactive components are comparatively small.
Also important, bone and fat have greater resistivity than do blood and muscle. As
current flows through the body, it is partitioned among different tissues according to
their individual resistivity and volumes. Thus, most of the current used in a body
impedance measurement flows through muscle, which has both large volume and
low resistivity.
Current will also pass through other body components, e.g., parenchyma and
lymph, but in smaller proportions reflecting their smaller volume fractions in the
２４
body. Moreover, muscle is far more conductive in a direction parallel to rather than
across the fibers, which means that current will preferentially flow along rather than
across the direction of muscle fibers.
D. Measurement conditions
Bio electrical impedance analysis has many merits such as noninvasive and easy
to perform. However, its repeatability is highly dependent on the measurement
conditions. Several studies revealed that measurement conditions are important in
bio impedance analysis. Measurement conditions refer to body posture, frequency
of current, electrode arrangement in tetra-polar body impedance measurement. This
is particularly important when repeated measurements are performed.13, 14
In this study, we specified body posture as sitting, supine, standing. And we
propose various kind of electrode arrangements and possible frequencies of current
to evaluate its performance for visceral fat measurement.
E. Finite element method
The finite element method is a numerical procedure for analyzing structures and
continua. Usually the problem addressed is too complicated to be solved
satisfactorily by classical analytical methods. The solution approach is based either
on eliminating the differential equation completely (steady state problems), or
rendering the partial differential equation into an approximating system of ordinary
２５
differential equations, which are then numerically integrated using standard
techniques such as Euler's method, Runge-Kutta, etc. The Finite Element Method is
a good choice for solving partial differential equations over complicated domains
(like cars and oil pipelines), or when the domain changes (as during a solid state
reaction with a moving boundary), and when the desired precision varies over the
entire domain, or when the solution lacks smoothness.
In this application such as body and injecting currents, we should consider
electrical and magnetic fields. Therefore we choose ‘COMSOL AC/DC MODULE’
for simulation which contains a set of application modes adapted to a broad
category of electromagnetic simulations. By electrical size of the structure we
choose quasi-static state. The physical assumption of these situations is that the
currents and charges generating the electromagnetic fields vary so slowly in time
that the electromagnetic fields are practically the same at every instant as if they had
been generated by stationary sources.
２６
2. H/W description of the visceral fat measurement
A. Specification of the system
The device of visceral fat measurement consists of constant current, voltage
measurement, demodulator, Micro controller unit. Table 1 shows the specifications
of the H/W system.
Table 1. Specification of the System
Number of Channels 4 Channels, Ag/Agcl electrodes
Magnitude of impedance 10 - 1000 ohms
Output range ± 5 V (analog)
Magnitude sensitivity 0.1 ohm
Operational Frequencies 50, 100 KHz
Current Output 400 ㎂ (rms)- constant sinusoidal current
Size (220x120x40)mm
２７
B. Digital system
We choose ATmega 128 (16 AU) as a Microcontroller, it has 10-bit ADC, serial
USARTs and 128[Kbyte] RAM and ROM memory. This system consists of a button
for system control, a sine wave generator, a C LCD ( 4×40) and LCD interface.
Figure 3 is the digital system diagram.
- DDS sine wave generator
AD9833 : CMOS complete DDS, 25 MHz speed, +2.3 ~ +5.5 V supply,
10 Bits resolution, 50 dB SNR, 10-pin SOIC Package,
Serial loading, Sinusoidal/Triangular DAC output, size (3.10 ×3.10 mm)
- Charcter LCD : 2 × 16 display (350 × 800 mm)
- ATmega 128 (16 AU): 8-bit Microcontroller, 10-bit ADC, serial USARTs
Master/Slave SPI serial interface, + 2.7 ~ +5.5 V supply
size (16.25×16.25 mm)
Figure 3. Digital system diagram
２８
a) 50 kHz, 560 mVpp
b) 100 kHz, 560 mVpp
Figure 4. Waveform of AD9833
２９
C. Analog system
We design the constant current circuit using TL074 (Low noise OP AMP) which
provide 400 ㎂ (50KHz, 100 KHz). ‘KFDA’ has recommended that under 100 ㎂
of current are safe under 1 kHz frequency, and under 1 ㎃ are safe over 1 kHz
frequencies. We use instrumentation AMP (AD620) for high input impedance, and
made peak detector using comparator (LM393 AD).
- Constant current
: 400 ㎂ constant current. range (10-1000 ohms)
TL074 cp ( Low noise quad OP AMP, ± 5 Vdc supply, 13V/µs slew rate )
-Voltage detector
: AD 620 (Low power Instrumentation Amplifier, ± 2.3 ~ 18 Vdc supply )
OPA124 (Low noise precision OP AMP, )
- Peak detector
: AC to DC. range (20 mV ~ 4000 mV)
LM 393 AD (Low offset voltage dual comparator, ± 1 ~ 18 Vdc supply )
Figure 5. Analog system diagram
３０
a) 50 kHz, 560 mVpp
b) 100 kHz, 560 mVpp
Figure 6. Peak detector output
３１
D. Evaluation of the H/W system
a) Impedance test 50 kHz
b) Impedance test 100 kHz
Figure 7. Impedance test results
３２
Table 2. Results of bio electrical impedance analyzer
We use 1% precision resistor as impedance variation which is on the x-axis and
y-axis means H/W output impedance value. When frequency is 50 kHz, its average
error rate is 2% and when 100 kHz, we got 1% error rate value.
３３
3. Abdomen modeling and FEM simulation
This finite element model was made simply consisting of muscle, fat
(subcutaneous fat, visceral fat) and bone. These regions were divided by Houns-
field Unit (HU) supported by ‘MIMIC’ program.
We made two models from 2 CT scans and the number of each mesh is 39,601
and 29,883. These models were evaluated by convergence study. And we
manipulate these models to make visceral fatty model (which has 5% more visceral
fat) and subcutaneous fatty model (which has 5% more subcutaneous fat).
Figure 8. CT, Abdomen level (Lumbar 4-5)
３４
Figure 9. Abdomen model (COMSOL, Lumbar 4-5)
Figure 10. Abdomen region dividing by MIMICS
３５
Table 3. Each properties at 100 kHz and HU values
MIMICS program provide Hounsfield unit for dividing each regions (fat, muscle,
bone) in CT scans. Table 3 shows their Hounsfield values and each properties
values in 100 kHz frequency.
Figure 11. Abdomen model 1, 2
３６
Table 4. Normal and manipulated model proportion ratio (a. model 1, b. model 2)
a) Model 1 normal, visceral fatty, and subcutaneous fatty model
b) Model 2 normal, visceral fatty, and subcutaneous fatty model
We made two models from 2 CT scans. Normal means each model’s natural
situation. And we manipulate its peritoneum boundary line to make visceral fatty
and subcutaneous fatty model. Therefore, we made each fatty model with 5% more
fat added. Table 4 shows the percentage of each fatty model for 2 models. By using
this finite element method (FEM) we freely manipulate model conditions and their
properties.
３７
Figure 12. Various electrode configurations
３８
We introduce various kind of electrode configuration. First of all, we propose one
configuration which arrange electrode with fixed waist ratio (waist /16). This
method is developed because most of others usually arrange electrodes with fixed
distance. We found fixed distance method is poor in distinguish fat and thin body
because they differ in their waist circumferences. And we assumed that electrodes
which arranged with the fixed ratio by waist circumference can be a solution to this
problem. We compare TANITA method with our proposed method. And we also
apply adjacent method which is being used in EIT (Electrical impedance
tomography).
Table 5. Permittivity and conductivity changes with frequencies
Table 5 is the permittivity and conductivity values of muscle, bone (cortical), and
fat which is variable with frequencies. We adopted these values in this experiment.
３９
III. RESULTS
1. Various electrode configurations
In this experiment, we compare various electrode configurations and evaluate its
performance by adopting ‘variation of V/S ratio’. This ratio is the ‘variant visceral
fat/ variant subcutaneous fat (∆V/∆S)’. It is for which configuration better reflect
visceral fat with less interference of subcutaneous fat. If one electrode
configuration’s ratio value is higher than others, this might be considered better
reflect visceral fat configuration than other electrode configurations. Hence our
purpose is to measure visceral fat more, this ratio is significant.
A. Electrodes with 1/16 waist ratio
Table 6. Measured voltage at each point A, B, C (V)
４０
a) model 1 - normal b) model 2- normal
c) model 1 - subcutaneous fatty d) model 2- subcutaneous fatty
４１
e) model 1 - visceral fatty f) model 2- viseral fatty
Figure 13. Electrodes with 1/16 waist ratio
Every simulation properties was same as 25 mV iso-potential lines, and 75
current injection lines. Therefore, by comparing only with those pictures, we can
assume which current injecting electrodes has better distribution in body and which
way the current goes through.
B. Electrodes with fixed distance
Table 7. Measured voltage with fixed distance
４２
C. Electrodes with adjacent method
Table 8. Measured voltage with adjacent method
Table 7 shows the voltage measured with fixed distance electrode configuraion
which was used in TANITA method. And Table 8 shows the voltage measured with
adjacent method. This method’s current injecting electrode is very near that the
current distribution is not irregular in body.
４３
a) model 1 - normal b) model 2- normal
c) model 1 - subcutaneous fatty d) model 2- subcutaneous fatty
e) model 1 - visceral fatty f) model 2- viseral fatty
Figure 14. Fixed distance electrode configuration
４４
a) model 1 - normal, belly current inject b) model 1- normal, right current inject
c) model 1 - normal, back current inject d) model 1- normal, left current inject
Figure 15. Model 1 with adjacent electrode arrangement
４５
a) model 2 - normal, belly current inject b) model 2- normal, right current inject
c) model 2 - normal, back current inject d) model 2- normal, left current inject
Figure 16. Model 2 with adjacent electrode arrangement
４６
2. Various frequencies configurations
In this experiment, we introduce various frequencies and simulate current
pathways. We set a hypothesis that using frequency variation we could measure
visceral fat and subcutaneous fat separately. In fact, high frequency current usually
penetrate into deep tissues and low frequency usually goes along with the surface of
the body. We choose 100 Hz as low frequency and 1 MHz, 1 GHz as high
frequencies and simulate current injection pathways, isopotential lines.
Table 9. Measured voltage with frequency variation
a) Model 1 with frequency variation
b) Model 2 with frequency variation
４７
a) model 1 - 100 Hz b) model 1- 100 kHz
c) model 1 - 1 MHz d) model 1- 1 GHz
Figure 17. Model 1 with frequency variation
４８
a) model 2 - 100 Hz b) model 2 - 100 kHz
c) model 2 - 1 MHz d) model 2- 1 GHz
Figure 18. Model 2 with frequency variation
４９
IV. DISCUSSION
Electrode configuration
We include various configuration of electrode arrangement in this study. And
electrode configuration with waist ratio has better performance than the fixed
distance by ∆V/ ∆S (Variation of V/S Ratio) index. We made this index for
comparing each electrode configurations in case of varying visceral fat. Current
electrode on each flank side has better performance than on the front and rear side.
Frequency variation
We assumed that using frequency variation we could measure visceral fat and
subcutaneous fat separately. Actually, according to changes of frequency, current
injection path seems different. At high frequencies, it penetrates into the deep tissue.
And at low frequencies, it usually goes along the outer part of body. However, it is
difficult to use frequency variation to measure visceral fat and subcutaneous fat
separately because our results showed current at low frequencies can also pass
thorough into inner part of the body. And for high difference between low and high
frequency (100 hz - 1 Ghz), we escape the range which is safe for human body.
Pre-study results
Our pre-study subjects were 6 healthy men and they were divided by waist into 3
groups (thin, normal, fat). Electrode arrangement with waist ratio and supine
posture is adapted. No remarkable changes between frequencies(25KHz- 100KHz)
and current densities (400-700㎂).
５０
V. CONCLUSION
Visceral obesity is significantly associated with the features of the metabolic
syndrome. And CT is the most well known and trusted method for measuring VFA.
However, it costs much and involves radiation exposure problem. BIA method is
simple and noninvasive for measuring VFA. But, the relation between impedance
and VFA is dependent on the measurement conditions
In this study, we introduce FEM (Finite Element Method) to find optimum
measurement conditions for measuring VFA and we also made a device for visceral
fat measurement system. Our impedance measuring device performance has
validated and we made models for finite element method. It has been limited by 2
models; however, this method has various advantages such as various condition
simulations, manipulating model conditions, cost savings etc. Results showed that
electrode configuration is important factor for measuring VFA and especially the
configuration with waist ratio has better reflect visceral fat than other configurations.
And these results showed strong correlation with our pre- studied results. Likewise,
using this method, we expect to set up the optimum conditions for measuring
visceral fat by BIA method.
５１
References
[1] Darcy B. Carr, Kristina M. Utzschneider, Rebecca L. Hull, Keiichi Kodama,
Barbara M. Retzlaff, John D. Brunsell et al., Intra-Abdominal Fat is a major
determinant of the national cholesterol education program adult treatment
panel Ⅲ criteria for the metabolic syndrome, Diabetes Aug 2004; 53:2087-94
[2] Shigenori Fujioka, Yuji Matsuzawa, Katsuto Tokunaga, and Seiichiro Tarui,
Contribution of Intra-abdominal fat accumulation to the impairment of glucose
and lipid metabolism in human obesity, Metabolism Jan 1987; 36:54-9
[3] Marcin Krotkiewski, Per Bjorntorp, Lars Sjostrom, and Ulf smith, Impact of
obesity on metabolism in men and women, The American society for clinical
investigation, Sep 1983; 72:1150-62
[4] Scott M. Grundy, James I. Cleeman, Stephen R. Daniels, Karen A. Donato,
Robert H. Eckel, Barry A. Franklin et al., Diagnosis and management of the
metabolic syndrome, Circulation 2005;112:2735-52
[5] K George M M Alberti, Paul Zimmet, Jonathan shaw, The metabolic syndrome-a
new worldwide definition, lancet 2005; 366:1059-62
[6] H Scharfetter, T Schlager, R Stollberger, R Felsberger, H Hutten, Assessing
abdominal fatness with local bioimpedance analysis: basics and experimental
findings, international journal of obesity 2001; 25: 502-11
[7] Masato Nagai, Hideaki Komiya, Yutaka Mori, Teruo Ohta, Yasuhiro Kasahara,
Yoshio Ikeda, Development of a new method for estimating visceral fat area
with multi-frequency bioelectrical impedance, Tohoku L. Exp. Med 2008;
５２
214:105-12
[8] Tokunaga K, Matsuzawa Y, Ishikawa K, Tarui S. A novel technique for the
determination of body fat by computed tomography. Int J Obes 1983; 7:437-45
[9] Tohru Yoshizumi, Tadashi Nakamura, Mitsukazu Yamane, Abdul Hasasn M.
Waliul islam, Masakazu Menju, Kouichi Yamasaki et al. Abdominal Fat:
Standardized Technique for Measurement at CT. Radiology 1999; 211:283-86
[10] Baker, L.E. Principles of the impedance technique. IEEE Eng. Med.
Biol. Mag. 1989; 8: 11-15.
[11] Nile M Oldham. Overview of bioelectrical impedance analyzers. American
Journal of Clinical Nutrition 1996; 64:405-12
[12] Kenneth R Foster and Henry C Lukaski, Whole body impedance- what does it
measure, American Journal of Clinical Nutrition 1996; 64:388-96
[13] Pinilla, J.C., Webster, B., Baetz, M., Reeder, B., Hattori, S. & Liu, L.
Effects of body positions and splints in bioelectrical impedance analysis. JPEN
J. Parenter Enteral Nutr, 1992; 16: 408-12
[14] Roos, A.N., Westendorp, R.G., Frolich, M. & Meinders, A.E. Tetrapolar
body impedance is influenced by body posture and plasma sodium
concentration. Eur. J. Clin.Nutr., 1992; 46: 53-60
[15] Lukaski, H.C., Bolonchuk, W.W., Hall, C.B. & Siders, W.A. Validation
of tetrapolar bioelectrical impedance method to assess human body
composition. J.Appl. Physiol., 1986; 60: 1327-32.
[16] Caterine, M.R., Yoerger, D.M., Spencer, K.T., Miller, S.G. & Kerber, R.E.
Effect of electrode position and gel application technique on predicted
transcardiac current during transthoracic defibrillation. Ann. Emerg. Med.,
1997; 29: 588-95
５３
[17] M. Yoneda, H. Tasaki, N. Tshchiya, H. Nakajima, T. Hamaguchi, S. Oku, T.
Shigal. A study of Bioelectrical Impedance Analysis Methods for Practical
Visceral Fat Estimation. International Conference on Granular Computing
2007. IEEE.109
[18] Miwa Ryo, Kazuhisa Maeda, Tohru Yamaguchi, Tomohiro Onda, Tohru
Funahashi, Makoto Nishida et al. A New simple method for the measurement
of visceral fat accumulation by bioelectrical impedance. Diabetes Care Feb
2005 ; 28,451-3
５４
<ABSTRACT (in Korean)>
복부 내장지방 측정을 위한 생체 임피던스 분석 시스템
<지도교수 유 선 국>
연세대학교 대학원 의과학과
김 광 수
과다한 복부 내 지방의 축적은 대사증후군을 일으키는 주요한 원인이
되어왔다. 복부 내 지방의 측정은 척추 Lumbar 4-5 번에 해당하는
CT를 촬영을 통한 측정 방법이 현존하는 가장 정확한 방법으로
여겨지고 있다. 하지만 그것에는 방사선 노출과 비용등과 같은 문제가
있어 지속적인 관찰이 필요한 대사증후군 관리에 있어 쓰이기
부적합하다고 여겨진다. 최근에는 내장지방의 면적을 측정하기 위한 생체
전기 분석법이 도입이 되어 많은 연구가 진행되고 있다. 그런데 정확한
측정을 위해 생체 전기 분석법은 측정조건이 중요한 요인이 된다.
그러므로, 이번 실험에서 우리는 유한 요소 해석 법을 도입하여 최적의
실험 조건을 찾았다. 실험에서 우리는 두 개의 복부모델을 만들었고
그들의 조건을 변형시킨 모델도 만들었다. 그리고 다양한 전극구성법과
주파수변화에 따라 내장지방과 피하지방을 분리하여 측정하는 방법을
시도해 보았다. 본 논문에서는 복부 내장지방 측정을 위한 하드웨어
시스템을 설계하고, 최적의 실험 환경을 구성하는 것을 목적으로 하였다.
핵심 되는 말: 대사증후군, 내장지방, 생체 전기 분석법, 측정 조건