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Magnetic Resonance Electrical Impedance Tomography

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(1)

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)

(2)

IIRC: Imped

a

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

(3)

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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

)

84

(4)

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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

(5)

IIRC: Imped

a

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c

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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 r

ECG

Amplifier

(

)

(;

)

(;

)

(;

tV

t

f

σ

∇⋅

=

rr

r

86

(6)

IIRC: Imped

a

n

c

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Research Center, Korea (h

ttp://iirc.khu.ac.kr) April 2008

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

87

(7)

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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

88

(8)

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April 2008

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

(9)

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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.

(10)

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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

(11)

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EIT using Boundary Measurements

EIT using Boundary Measurements

Ne

umann

(Boundary

Current)

Dirichlet

(Boundary

Voltage)

(12)

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April 2008

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. Smallw

ood, 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 93

(13)

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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

(14)

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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

(15)

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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

(16)

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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)

(17)

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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 y

j

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

98

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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 Echo

G

r

G

s t

I

Tc2 Tc1 99

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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

(20)

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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

102

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MRI Scanner:

MRI Scanner:

3T Scanner at IIRC

3T Scanner at IIRC

103

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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

104

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Recessed Electrodes

Recessed Electrodes

B

z

Image

MR Magnitude Image

Phantom

Recessed

Electrodes

(25)

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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)

(26)

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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)

107

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Agar Phantom:

Agar Phantom:

M

M

and

and

Φ

Φ

Images

Images

Wrapped

Phase

Image

Magnitude

(28)

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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 3

Homogeneous Phantom

(L

2

-error = 3.2%)

Agar Object Phantom

(L

2

-error ~ 5%)

[S/m]

[S/m]

(30)

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ttp://iirc.khu.ac.kr) April 2008 -1.5 -1 -0.5 0 0.5 1 1.5 2 x 10 -7

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 E2

ab

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 E2

ab

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.

(31)

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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

112

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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 0.76

Conductivity values were measured after experiments by an impedance analyzer using the four-electrode method.

(33)

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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 in

B

B

zz

B

B

zz

M

M

Horizontal Injection

Vertical In

114

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Tissue Phantom:

Tissue Phantom:

B

B

z

z

Images

Images

B

B

zz

B

B

zz

M

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 in

M

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, “Elect

rical conductivity images of

biological ti ssue phantoms in MR EI T,” Physiol. Meas. , vol. 26, pp. S279-S288, 2005. 116

(36)

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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, “Elect

rical conductivity images of

biological ti ssue phantoms in MR EI T,” Physiol. Meas. , vol. 26, pp. S279-S288, 2005. 117

(37)

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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)

118

(38)

Estimation 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+07

http://niremf.ifa

c.cnr.it/tissprop/

Gabriel C et al, P

h

ys. Med. Biol. 1996;41:2231-2293

(39)

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 1 132

Gall 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

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ys. Med. Biol. 1996;41:2231-2293

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Dielectric anatomical model of permittivity and

conductivity at 120 MHz and 1 GHz

Mazzurana

M et al, Phys. Med. Biol. 2003;48:3157-3170

(41)

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