IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr)
Hyung
Hyung
Joong
Joong
Kim
Kim
Impedance Imaging Research Center (IIRC)
Impedance Imaging Research Center (IIRC)
Department of Biomedical Engineering
Department of Biomedical Engineering
Kyung
Kyung
Hee
Hee
University, KOREA
University, KOREA
Magnetic Resonance
Magnetic Resonance
Electrical Impedance
Electrical Impedance
Tomography (MREIT)
Tomography (MREIT)
IIRC: Imped
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n
c
e Imaging
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ttp://iirc.khu.ac.kr)
April 2008
Contents
Contents
•
Introduction and Motivation
•
Electrical Impedance Tomography (EIT)
•
Magnetic Resonance Electrical
Impedance Tomography (MREIT)
–
Basics and requirements
–
Agar phantom experiments
–
Tissue phantom experiments
–
Animal experiments
•
Application & summary
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Volume Conductor Field
Volume Conductor Field
•
Conductivity,
σ
•
Internal current source,
f
•
External injection current,
I
•
Geometry (boundary shape and size)
•
Measurable quantities
–
Boundary v
o
ltage and li
mited internal voltage
–
Boundary or ex
it
curre
nt a
nd limited internal current
–
External and/or internal magn
etic flux density
E1
E2
Ω
∂Ω
I
I
(
σ
,
f,
V
,
J
,
B
)
84IIRC: Imped
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April 2008
Volume Conductor Field
Volume Conductor Field
•
White lines are current stream lines.
•
Black lines are equipotential lines.
V
σ
=
−∇
J
()
Vf
σ
∇
⋅∇
=
−
0 o
n
V
n
σ
∂
−
=∂
Ω
∂
+
-+
-85
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Bio
Bio
--
electric Signal
electric Signal
Medical Instrumentati o n: Applicati on and Design, 3 rd ed., by J. G. Webste rECG
Amplifier
(
)
(;
)
(;
)
(;
tV
t
f
σ
∇⋅
∇
=
−
rr
r
86IIRC: Imped
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n
c
e Imaging
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Bio
Bio
--
magnetic Signal
magnetic Signal
(;
)
(;
)
(;
)
tt
V
t
σ
=−
∇
J
rr
r
(
)
(;
)
(
;
)
(;
)
tV
t
f
t
σ
∇⋅
∇
=
−
rr
r
f(
r;
t)
J
(r
;t
)
Ω
MEG
0
3
'
(;
)
(
';
)
'
4
'
tt
d
v
μ
π
Ω
−
=×
−
∫
rr
Br
J
r
rr
87IIRC: Imped
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Hepatic Tumor Conductivity
Hepatic Tumor Conductivity
D. Haemmeric h , S. T. Staelin, J. Z. Tsai, S. Tungjitkusol mun, D. M . M ahv i a nd J . G. Webster, “In vivo
electrical conductivity of hepatic tumours,” Physiol. Meas.
, vol. 24, pp. 2 51–260, 2003.
Normal Cells
Tumor
Necrosis
Fibrosis
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Breast Tumor Conductivity
Breast Tumor Conductivity
A. J. Surowiec, S. S.
Stuchly, J. R.
Barr, and A. Swarup, ”D
iel
e
ctric properti
es
of breast carcinom
a and the surroundi
ng
tissues,”
IEEE Trans. Biom
ed. Eng.
, vol. 3
5
, no. 4,
pp. 257–263, 1988.
Normal
Tissue
Lobular
Carcinoma
Ductal
Carcinoma
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Conductivity and Neural Activity
Conductivity and Neural Activity
•
C
ole K S and Cur
tis H J 1939 Electrical
impedance of the squid giant axon during
activity
J. Gen. Physio
l.
22 649-670
•
C
ole K S 1949 Dynamic electrical char
acteristics of squid axon membr
ane
Arch.
Sci. Physiol.
3 253-258
•
A
dey
W
, Kado
R and Didio
J
1962 Impedanc
e measurements in brain tissue of
animals using microvolt s
ignals
Exp. Neruol.
5
47-66
•
V
an-Harreveld
A and Schade
J 1962 Changes in
the electr
ical conductivity of
cerebral cor
tex during seizure activity
Exp. Neurol.
5 383-400
•
R
ank J B 1963 Specific impedance
of rabbit cerebral cor
tex
Exp. Neurol.
7
144-152
•
A
ladjolova
N
A 1964 Slow electr
ical processes in the brain
Prog. Brain Res.
7
155-237
•
G
eddes L A and Baker L E 1967
The specific resistance of biological material: a
compendium of data for
the biomedical engineer and physiologist
Med. Biol. Eng.
271-293
•
M
eister
M, Pine J, Baylor
, DA 1994 Mu
lti-neuronal signals from the retina:
acquisition and analysis
J. Neurosci. Meth.
51 95-106
Neural activity produces
3-5% local conductivity changes at low frequency.
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Motivation and Goal
Motivation and Goal
•
P
hysiological functions and pathological changes
alter conductivity values.
•
N
eural activity induces changes in conductivity.
•
S
ource imaging needs conductivity values.
•
E
lectromagnetic stimulations need conductivity
values.
Cross-sectional Imaging of
Internal Conductivity
and Current Density Distribution
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EIT using Boundary Measurements
EIT using Boundary Measurements
Ne
umann
(Boundary
Current)
Dirichlet
(Boundary
Voltage)
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M. Cheney, D. Isaacson, and
J. C. Newell, “Electrical im pedance t o m o graphy ,” SIAM Rev. , vo l. 41, p p . 8 5 -1 0 1 , 1999. Phantom (Salin e + Agar) Static Imag e o f
ρ
Thorax @RV @FRC @PTV (w.r.t TLC ) P. Metheral l, D. C. barber, R. H. Smallwood, and B. H. Brown,
“Three-dimensional electri c al im pedance t o m o gr aphy ,” Nature , vol. 380, pp . 509-512, 1996. P. M e th er all, Three D im ensional Electrical I m pedanc e Tom ography of the Hum an Thorax , PhD Thesi s, Dept. of Med. Ph y s. And Cli n. En g ., Univ. of Sheffiel d, Sheffiel d, UK, 1998.
EIT Images:
EIT Images:
Thorax
Thorax
Thorax @ Expiration Thor ax @ Inspiration 93IIRC: Imped
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EIT Images:
EIT Images:
Brain
Brain
A. T. Tidswell, A. Gibson, R. H. Bayford, and D. S.Holder, “Three-dimensional elec
trical i m pedanc e tomography of human brai n activity,” Neur oI mage , vol. 13, pp. 283-294, 2001. 94
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Static Imaging
Static Imaging
with High Spatial Resolution
with High Spatial Resolution
•
Internal measurements
•
Non-invasive measurements
•
Non-contact measurements
•
Spatial information encoded in
measured data
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Magnetic Resonance Electrical
Magnetic Resonance Electrical
Impedance Tomography (MREIT)
Impedance Tomography (MREIT)
Reconstruct cross-sectional images
of conductivity and current density
distribution
Internal magnetic flux density
measurements
using MRI
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April 2008
How to Measure Magnetic Field?
How to Measure Magnetic Field?
M. L. G. Joy, G. C. Scott, and R. M. Henkelman, “
In vivo
detection of applied
electric currents by magnetic resonance imaging,”
Mag. Reson. Imag.
, vol.
7,
pp. 89-94, 1989.
G. C. Scott, M. L. G. Joy, R. L.
Armstrong,
and
R.
M.
Henkelman,
“Measurement of nonuniform
current
density
by magnetic resonance,”
IEEE
Trans. Med. Imag.
, vol. 10, no. 3, pp. 362-374, 1991.
z
Current injection MRI technique
z
Originally developed for Current
Density Imaging (CDI)
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April 2008
Basics of MREIT Experiment
Basics of MREIT Experiment
B
0
Electrode
Lead Wire
SE Pulse
Sequence
Experimental Setup
(,
)
(
)
(,
)
(,
)
(
,
)
qc x yj
B
xyT
j
xm
k
yn
k
jx
y
q
Sm
n
M
x
y
e
e
e
d
xd
γ
δ
∞
±Δ
+
Δ
±
−∞
=
∫∫
Raw Data
Magnitude Image
P
hase Image
98IIRC: Imped
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SE Pulse Sequence
SE Pulse Sequence
RF
G
p TE TE/2 TE/2 t t t 90 o 180 o t Spin EchoG
rG
s tI
Tc2 Tc1 99IIRC: Imped
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Magnetic Flux Density (
Magnetic Flux Density (
B
B
z
z
) Imaging
) Imaging
We use both positive and negative injection currents.
Inverse Fourier Transform
Compute phase and unwrap phase
k-space data collection
Scaling and slice or
dering
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B
B
z
z
--
based Algorithms
based Algorithms
•
Harmonic
B
z
Algorithm
(1,2)
•
Gradient
B
z
Decomposition Algorithm
(3,4)
•
Variational Gradient
B
z
Algorithm
(5,6)
•
Other Algorithms
–
Multiple boundary voltage data
–
H
ybrid algorithms
–
A priori
structural information
–
Other new algorithms
(1)
Seo
et al.
, “Reconstruction of conductivity
and current density ima
ges usi
ng only one compon
ent of magnetic fiel
d
measurements,”
IEEE Trans. Biom
ed. Eng. , vol. 50, no. 9, pp. 1121-1 124, 2003 . (2) Oh et. al. , “Conductivi
ty and current density im
age reconstruction using harmonic Bz algo rith m in MREIT," Phys. Med . Biol. , vol. 4 8 , Sep., vol . 48, pp. 3 1 01-3 1 1 6 , 2 0 0 3 . (3) Seo et al.
, “Reconstruction of current density di
stributions in axially symmetric
cylindr
ical sections usi
ng one component of
magnetic flux density: comp
uter simul a ti on study," Physi ol. Meas. , vol. 24, pp. 565-577, 2003. (4) Park et al. , “Electrical con ductivity
imaging using gradi
ent Bz decompositi on algorithm in ma gneti c reso na nce el ectrical im pedance t o m o gr aphy ( M R EI T ), "
IEEE Trans. Med. Im
aging , vol . 28, pp. 388-394, 2004. (5) Park et al ., "Static con ductiv ity ima g
ing using variational gradi
ent Bz algorithm i n magneti c resonance el ectrical im pedance t o m o gr aphy ( M R EI T ), " Physiol. Meas. , v o l. 25, pp. 257-269, 20 04 . (6) Kwon et al. , “Electrical con d uctivity ima g in g using a variati onal met hod in Bz -b ased MR EI T,” Inv. Prob. , vo l. 21, pp. 96 9 -980, 2005. 101
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Experimental MREIT Studies
Experimental MREIT Studies
•
MRI scanner:
3T, 11T, 17T, and 9.4T
•
Imaging objects:
phantoms and animals
•
R
ecessed electrodes
•
C
urrent source
•
P
ulse sequence:
SE and GE
•
S
oftware:
MREIT toolbox
102IIRC: Imped
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MRI Scanner:
MRI Scanner:
3T Scanner at IIRC
3T Scanner at IIRC
103IIRC: Imped
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Imaging Objects
Imaging Objects
•
C
onductivity Phantoms
–
S
aline
–A
g
a
r
–
P
olyacrylamide
–
S
ponge
–
C
otton thread and fabric
–
S
ilk thread and fabric
–
Sausage, fruit, and vegetable
•
T
issue Phantoms
–
B
iological tissues
–A
g
a
r g
e
l
•A
n
im
a
ls
–P
ig
–D
o
g
–
O
thers
•H
u
m
a
n
104IIRC: Imped
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Recessed Electrodes
Recessed Electrodes
B
zImage
MR Magnitude Image
Phantom
Recessed
Electrodes
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MREIT Current Source
MREIT Current Source
PC & Spectrometer Interface Mi c ro -controller Switchi n g Circuit DAC Howland Cur rent Pump Circuit
Voltmeter (IA and
ADC)
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Agar Phantom:
Agar Phantom:
Setup
Setup
Phantom
MRI parameters
TR/TE = 1400/60ms
FOV = 200mm
Mat
rix size =
128
×128
Slice thickness/Gap
=
3/0mm
Number of slices = 8
Average =
2
Current amplitude = 27mA
Current pulse width = 24ms
Voxel size(x,y,z) = 1.5625
×1.5625
×3mm
3
Phantom
Solution : 2S/m (Na
Cl=12.5g/l, Cu
SO
4
=2g/l)
Object (agar) : 0.5S/m (Na
Cl=2g/l, Cu
S
O
4=2g/l, Agar=1
5g/l)
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Agar Phantom:
Agar Phantom:
M
M
and
and
Φ
Φ
Images
Images
Wrapped
Phase
Image
Magnitude
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Agar Phantom:
Agar Phantom:
B
B
z
z
Images
Images
Horizontal Injection
Curren
t
Vertical Injection Current
-6 -4 -2 0 2 4 6 x 10 -8 -6 -4 -2 0 2 4 6 x 10 -8 109
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Agar Phantom:
Agar Phantom:
σ
σ
Images
Images
1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3Homogeneous Phantom
(L
2-error = 3.2%)
Agar Object Phantom
(L
2
-error ~ 5%)
[S/m]
[S/m]
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Resolution Phantom:
Resolution Phantom:
Setup
Setup
MR Magnitude Image
Magnetic
F
lux Density
I
m
age (
B
z)
4 3 2 140 60 30 1 σ 1 σ 140 E1 E3 E4 E2 E4 E2ab
2 σ 3 σ 2 σ 3 σ I1 I1 I2 I2 140 60 30 1 σ 1 σ 140 E1 E3 E4 E2 E4 E2ab
2 σ2 σ 3 σ3 σ 2 σ2 σ 3 σ3 σ I1 I1 I1 I1 I2 I2 I2 I2 S. H. Oh, B. I . Lee, T . S. Park, S. Y. Lee, E. J. Woo, M. H. Cho, O. Kwon, and J. K.Seo, “Magnetic resonance
electrical i
m
pedance tomography
at 3 Tesla fiel
d strength,”
Mag. Reson. Med.
, 1292-1296, 2004.
IIRC: Imped
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ttp://iirc.khu.ac.kr) April 2008 [S/m] 0 0.2 0.4 0.6 0.8 1 [S/m] [S/m] 0 0.2 0.4 0.6 0.8 1 [S/m] S. H. Oh, B. I . Lee, T . S. Park, S. Y. Lee, E. J. Woo, M. H. Cho, O. Kwon, and J. K.
Seo, “Magnetic resonance
electrical i
m
pedance tomography
at 3 Tesla fiel
d strength,”
Mag. Reson. Med.
, 1292-1296, 2004.
MR Magnitude Image
Resolution Phantom:
Resolution Phantom:
σ
σ
Images
Images
σ
at slice #3
σ
at slice #4
σ
at slice #1
σ
at slice #2
112IIRC: Imped
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Tissue Phantom:
Tissue Phantom:
Setup
Setup
140mm
140mm
Chicken
Breast
Porcine
Muscle
Bovine
Tongue
Agar G
e
latin (1g/l
CuSO
CuSO
4 4, 3.125
, 3.125
g/l
g/l
NaCl
NaCl
, 7g/l A
g
ar)
, 7g/l A
g
ar)
Conductivity [S/ m ] Tissue Longitudinal Tran sversal Chicken Breast 0.60 0.55 Bovine Tongue 0.41 0.36 Porci n e Muscle 0.64 0.55 Bovine Liver 0.69 0.69 Agar Gelatin 0.76 0.76Conductivity values were measured after experiments by an impedance analyzer using the four-electrode method.
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Tissue Phantom:
Tissue Phantom:
B
B
z
z
Images
Images
Bovine Live r Chick en Bre ast Porcine Mus cle Blood Vessel (Air) Re cessed El ec trode Agar Gelat inB
B
zzB
B
zzM
M
Horizontal Injection
Vertical In
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Tissue Phantom:
Tissue Phantom:
B
B
z
z
Images
Images
B
B
zzB
B
zzM
M
Horizontal Injection
Vertical In
jection
Bovine Tongue Chick
en Bre ast Porcine Mus cle Air Bubble Re cessed El ec trode Agar Gelat in 115
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Tissue Phantom:
Tissue Phantom:
σ
σ
Image
Image
Bovine Live r Chick en Bre ast Porcine Mus cle Blood Vessel (Air) Re cessed El ec trode Agar Gelat inM
M
σ
σ
[S/m]
Tissue
Measur
ed Conductivity [S/m]
Reconstructed Conductivity [S/m]
Agar Gelatin
0.76
0.73
Bovine Liver
0.69
0.64
Porcine Muscle
0.55 –
0
.64
0.59
C
h
ic
k
en B
reas
t
0.55 –
0
.60
0.54
S. H. Oh, B. I. Lee, E. J. Woo, S. Y. Lee, T . S. Kim, O. Kwon, and J. K. Seo, “Electrical conductivity images of
biological ti ssue phantoms in MR EI T,” Physiol. Meas. , vol. 26, pp. S279-S288, 2005. 116
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Tissue Phantom:
Tissue Phantom:
σ
σ
Image
Image
M
M
σ
σ
Bovine Tongue Chick
en Bre ast Porcine Mus cle Air Bubble Re cessed El ec trode Agar Gelat in 0 0.2 0.4 0.6 0.8 1
[S/m]
Tissue
Measur
ed Conductivity [S/m]
Reconstructed Conductivity [S/m]
Agar Gelatin
0.76
0.73
Bovine Tongue
0.36 –
0
.41
0.44
Porcine Muscle
0.55 –
0
.64
0.59
C
h
ic
k
en B
reas
t
0.55 –
0
.60
0.52
S. H. Oh, B. I. Lee, E. J. Woo, S. Y. Lee, T . S. Kim, O. Kwon, and J. K. Seo, “Electrical conductivity images of
biological ti ssue phantoms in MR EI T,” Physiol. Meas. , vol. 26, pp. S279-S288, 2005. 117
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Tissue Phantom:
Tissue Phantom:
σ
σ
Images
Images
M
M
σ
σ
(48mA)
(48mA)
σ
σ
(12mA)
(12mA)
σ
σ
(upper s
lic
e)
(upper s
lic
e)
σ
σ
(middle slice)
(middle slice)
σ
σ
(lower slice)
(lower slice)
118Estimation of the dielectric properties of
biological materials at 100 Hz
Tissue Conductivity [S/m] Relative permittivity Air 0 1 Aorta 0 .27789 5 .0921e+06 Blood 0.7 5 259.8 Blood Vessel 0.27789 5 .0921e+06 Bod y Fluid 1 .5 98.999 Bone Cancellous 0.081031 217030 Bone Cortical 0.020059 5852.8 Bone Marrow 0 .001823 69898 Breast Fat 0 .023239 327610 Cartilage 0 .17215 4 90460 Tissue Conductivity [S/m] Relative permittivity Fat 0 .02081 4 57060 Gland 0 .52211 4 92030 L y mph 0 .52211 4 92030 Mucou s Membrane 0.00046112 45298 Muscle 0 .26671 9 .329e+06 Nail 0.020059 5852.8 Nerve 0 .028042 466020 Skin Dr y 0 .0002 1135.9 Skin Wet 0 .00046112 45298 Tendon 0.30479 1 .1857e+07http://niremf.ifa
c.cnr.it/tissprop/
Gabriel C et al, P
h
ys. Med. Biol. 1996;41:2231-2293
Estimation of the dielectric properties of
biological tissue at 100 Hz
Tissue Conductivity [S/m] Relative permittivity Bladder 0 .20558 1 92840 Brain Grey Matter 0 .089018 3.9061e+06 Brain White Matter 0.058093 1.6677e+06 Cerebellum 0.10902 3 .9064e+06 Cerebrospinal Fluid 21 0 9 Cervix 0.41134 2 .0139e+07 Colon 0 .12134 2 .0091e+07 Dura 0.50056 1 9486 Gall Bladder 0 .90001 1 132Gall Bladder Bile
1.4 1 20 Heart 0 .093565 3.1637e+06 Kidney 0 .10216 3 .5181e+06 Lens 0.32216 5 90870 Liver 0.03813 6 78470 Tissue Conductivity [S/m] Lung Deflated 0 .20588 Lung Inflated 0 .072979 Oesophagus 0.52211 Ovary 0 .32211 Pancreas 0.52211 Prostate 0.42211 Retina 0.50283 Small Intestine 0 .52241 Spinal Cord 0.028042 Spleen 0.095662 Stomach 0.52211 Testis 0.42211 Th y roid 0 .52211 Tongue 0.27211 Tooth 0.020059 Uterus 0.29009
http://niremf.ifa
c.cnr.it/tissprop/
Gabriel C et al, P
h
ys. Med. Biol. 1996;41:2231-2293
Dielectric anatomical model of permittivity and
conductivity at 120 MHz and 1 GHz
Mazzurana
M et al, Phys. Med. Biol. 2003;48:3157-3170
IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr)
Animal Experiment:
Animal Experiment:
Setup
Setup
122IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr) April 2008
Animal Experiment:
Animal Experiment:
Pre
Pre
--
processing
processing
MR Image
Pre-processing
•
Shape extraction
–
Boundary
–
Electrode position
•
Phase unwrapping
•
Meshing
•
Extraction of interior regions
with very low SNR in
B
z•
B
zdata filling by
∇
2B
z= 0
123IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr)
Animal Experiment:
Animal Experiment:
B
B
z
z
Images
Images
MR Magnitude
Image
B
zImage
B
zImage
124IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr) April 2008
Animal Experiment:
Animal Experiment:
σ
σ
Image
Image
MR Magnitude
Image
0 0.5 1 1.5 2 2.5 3[S/m]
Conductiv
ity
Image
125IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr)
Animal Experiment:
Animal Experiment:
Subject
Subject
1)
Weight : 11Kg
2)
Length : about 700mm
3)
Diameter (chest): about 150mm
Liver
Rib
IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr) April 2008
Animal Experiment:
Animal Experiment:
B
B
z
z
Image
Image
[Tesla]
5
0
-5
x 10
-8[Tesla]
5
0
-5
x 10
-8B
zfor
Horizontal
Injecti
o
n
B
zfor
Vertical
Injecti
o
n
MR Magnitude Image
127IIRC: Imped
a
n
c
e Imaging
Research Center, Korea (h
ttp://iirc.khu.ac.kr)