Magnetic Resonance Electrical Impedance Tomography (MREIT)web.yonsei.ac.kr/nipi/lectureNote/MREIT(ISMRM2011) by Woo.pdf · IIRC, KHU Magnetic Resonance Electrical Impedance Tomography

IIRC, KHU Magnetic Resonance Electrical Impedance Tomography (MREIT) May 2011

Magnetic Resonance ElectricalImpedance Tomography (MREIT)As Electromagnetic Tissue Property Imaging Modality

Eung Je Woo

Department of Biomedical EngineeringImpedance Imaging Research Center (IIRC)

Kyung Hee UniversityKorea

[email protected]

mailto:[email protected]


Contents Introduction

• Electromagnetic Tissue Property Imaging• Conductivity and Permittivity• Electrical Impedance Tomography (EIT)

MREIT Research at IIRC

Technical Problems in MREIT

Future Directions


Acoustic impedance Proton density and MR phenomena Oxygen and water diffusion Optical absorption, scattering, and emission X-ray attenuation γ-ray emission

Image Contrast


Acoustic impedance Proton density and MR phenomena Oxygen and water diffusion Optical absorption, scattering, and emission X-ray attenuation γ-ray emission Electrical conductivity Electrical permittivity Magnetic susceptibility Neural activity Biochemistry

Image Contrast

Electromagnetic Tissue Property

Electromagnetic Source


Medical Imaging Modality Ultrasound MRI OCT X-ray PET

Source Imaging MRE MREIT EIT MAT-MI MIT MREPT QSM Microwave Tomography Terahertz Imaging DOT

What are differences?

- Linear vs. nonlinear

- High vs. low sensitivity

- Well- vs. ill-posedness


Electromagnetic Tissue Property Imaging

Electrical Impedance Tomography (EIT) Admittivity (conductivity and permittivity) imaging Frequency range: 10 Hz to 1 MHz Difference imaging

Magnetic Induction Tomography (MIT) Microwave Tomography Magneto-Acoustic Tomography – Magnetic Induction (MAT-MI)

MR Electrical Impedance Tomography (MREIT) Conductivity imaging Frequency range: below 1 kHz Static imaging

MR Electrical Property Tomography (MREPT) Admittivity (conductivity and permittivity) imaging Frequency : Larmor frequency (128 MHz at 3 T) Static imaging

Quantitative Susceptibility Mapping (QSM)


Conductivity and Resistance

V -Cl

-e

-e

+Na

I

I

V

-eI

-eI

-Cl+Na

dc=J vd µ=v E c uµ σ σ= = = − ∇J E Eu= −∇E q=F E

L

S

, ,

1 , 1

V V VE J E I JS SL L L

L L VV I I RIS S

LI

RS

σ σ σ

ρσ σ

= = = = =

= = = = =

Mobile Ions


Permittivity and Capacitance

V+-+-

+-+-

+-+-

+-+-

+-+-

+-+-

+-+-

+-+-

+-+-

V-+-+

-+-+

-+-+

-+-+

-+-+

-+-+

-+-+

-+-+

-+-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-+

-e

-e- - - - - - - - -

+ + + + + + + + +

-e

-e+ + + + + + + + +

- - - - - - - - -+Q

-Q +Q

-Q

L

S

( ) ( )( )

Q V V

dQ t dv ti t Cdt

SC

dt

Lε= =

= =

( ) sin( ), ( ) cos( )10, 90 ,

v t V t i t V C t

V V Cj C

ω ω ω

ωω

= =

= ∠ = ∠ = =VV I ZI

PolarizationImmobile Polar Molecules


i(t) ~

Cell and Bio-impedance

1

1

2

2

RCCR

1 21 2

1 1R jX R Rj C j Cω ω

= + = + + +Z

-Cl+Na

-Cl+Na

+Na -Cl

+ + + + + + +

+ + + + + + +

_ _ _ _ _ _ _

_ _ _ _ _ _ _

Cell Membrane

Extra-cellular Fluid

Intra-cellular Fluid

cos , sinR jX Z

R Z X Zθ

θ θ= + = ∠= =

Z( )( )

( ) sin and

( ) sinm

m

i t I t

v t I Z t

ω

ω θ

=

= +

i(t) ~

+

v(t)

−

+

v(t)

−


Cell Structures in TissuesExtra-cellular

Fluid

Intra-cellularFluid

CellularMembrane

( , ) ( , )( , )

(, ) (( , )) c

ω ω

σ

σ

µω

ω

ω

=

=

J r E r

r

r

r r

• Ion Concentration

• Ion Mobility


Simple Case 1

Homogeneous Object

I

I

LowFrequency

Current

HighFrequency

Current

Macroscopic Conductivity Seen by the Current

(( ), () ) ,cσ µ ωω = r rr


Simple Case 2

Insulating MembraneFilled with the Same Saline

I

I

LowFrequency

Current

HighFrequency

Current

(( ), () ) ,cσ µ ωω = r rr



Simple Case 3

I

I

LowFrequency

Current

HighFrequency

Current

Insulating Membrane with HolesFilled with the Same Saline

(( ), () ) ,cσ µ ωω = r rr



Simple Case 4

I

I

LowFrequency

Current

HighFrequency

Current

Insulating Membrane with HolesFilled with the Same Saline

(( ), () ) ,cσ µ ωω = r rr



Simple Case 5

Solid Anomaly withConductivity Contrast

I

I

LowFrequency

Current

HighFrequency

Current

(( ), () ) ,cσ µ ωω = r rr



Admittivity of Biological Tissue

Molecular composition of cells Shape and direction of cells Density and structure of cells Intra- and extra-cellular fluids Concentration and mobility of ions Temperature Probing method including frequency and

electrode configuration

( ) ( ) ( ), , j ,γ ω σ ω ωε ω= +r r r


Breast Tissues

A. J. Surowiec, S. S. Stuchly, J. R. Barr, and A. Swarup, ”Dielectric properties of breast carcinoma and the surroundingtissues,” IEEE Trans. Biomed. Eng., vol. 35, no. 4, pp. 257–263, 1988.

NormalTissue

LobularCarcinoma

DuctalCarcinoma


Liver Tissues

D. Haemmerich, S.T. Staelin, J. Z. Tsai,S. Tungjitkusolmun,D. M. Mahvi and J.G. Webster, “In vivoelectricalconductivity ofhepatic tumours,”Physiol. Meas., vol.24, pp. 251–260,2003.

Normal Cells Tumor

NecrosisFibrosis


Conductivity and Neural Activity Cole K S and Curtis H J 1939 Electrical impedance of the squid giant axon during

activity J. Gen. Physiol. 22 649-670 Cole K S 1949 Dynamic electrical characteristics of squid axon membrane Arch.

Sci. Physiol. 3 253-258 Adey W, Kado R and Didio J 1962 Impedance measurements in brain tissue of

animals using microvolt signals Exp. Neruol. 5 47-66 Van-Harreveld A and Schade J 1962 Changes in the electrical conductivity of

cerebral cortex during seizure activity Exp. Neurol. 5 383-400 Rank J B 1963 Specific impedance of rabbit cerebral cortex Exp. Neurol. 7 144-152 Aladjolova N A 1964 Slow electrical processes in the brain Prog. Brain Res. 7 155-

237 Geddes 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. 5 271-293

Meister M, Pine J, Baylor, DA 1994 Multi-neuronal signals from the retina: acquisition and analysis J. Neurosci. Meth. 51 95-106

Neural activity produces 1-5% local conductivity changes at low frequency.


Action Potential

-+

Current Source

Crab Nerve V1 V2

Action Potential

-5

0

5

10

mV

2245

2250

2255

2260

2265

Time (msec)

R (o

hms)

Resistance0 10 20 30 40 50

-2

0

2

4

6

8

CA

P [m

V]

0 10 20 30 40 50-1

0

1

2

Time [ms]

∆σ

[%]

CAP

∆σ

Conductivity of Crab Nerve

From D. Holder and T. I. Oh


Functional & Pathological Changes Regional Lung Ventilation Perfusion Pulmonary Edema Cardiopulmonary Functions Hemorrhage Ischemia Stomach Emptying Visceral Fat Brain Functions Neural Activity Tumor Others


( ) ( )( )( ) ( )

0 in on

uu g

σσ

∇⋅ ∇ = Ω− ∇ ⋅ = ∂Ω

r rr r n

( ) ( ) ( ) ( ) ( )uσ σ== − ∇J r r r r E r

( ) ( ) ( )03

' ''4 '

dµπ Ω

× −=

−∫

J r r rB r r

r r

1E2EΩ

∂Ω

I I

n

L− L+

a

(σ, u, J, B)

(g)

Probing by Injecting Current


Numerical Example using FEM

B. I. Lee, S. H. Oh, E. J. Woo, S. Y. Lee, M. H. Cho, O. Kwon, J. K. Seo, J. Lee, and W. S. Baek, “Three-dimensional forward solver and its performance analysis for MREIT using recessed electrodes," Phys. Med. Biol., vol. 48, 1972-1986, 2003.

σ

u

1E

2E

yx

yx

[S/m]

Bx

By

Bz

yx

yx

yx

Jx

Jy

Jz

yx

yx

yx

[mV]

[Tesla]

[Tesla]

[Tesla]

[mA/mm2]

[mA/mm2]

[mA/mm2]


EIT and MREIT

EIT (Electrical Impedance Tomography)- Admittivity imaging from 10 Hz to 1 MHz- Boundary current-voltage measurement- Time- or frequency-difference imaging- Low spatial resolution- High temporal resolution- Functional imaging

MREIT (Magnetic Resonance EIT)- Conductivity imaging below 1 kHz- Internal magnetic flux density measurement- Absolute or contrast imaging- High spatial resolution- Low temporal resolution- Static and functional imaging


EIT

( ) sin( )p mi t I tω=

( ) sin( )q pq mv t Z I tω θ= +

Ip=Im∠0

Vq=ZpqIm∠θ

Zpq=Zpq∠θp

q

i

V

( ) ( )( )( ) ( )

0 in on

uu g

ω ω

ω ω

γγ

∇⋅ ∇ = Ω− ∇ ⋅ = ∂Ω

r rr r n

( ) ( ) ( )jωγ σ ωε= +r r r

(Electrical Impedance Tomography)


Data Collection Protocol

Neighboring Method

(10-4-10-6V)

(10-3-10-4A)


Difference Imaging in EIT

If admittivity changes as

boundary voltage changes accordingly as

When δγ is small, by a linearization.

A difference image is by tSVD, for example.

2 1 ,γ γ δγ= +

2 1.u u uγ γ δ= +

u γδ δγ= S† uγδγ δ= S

2 1T Tu u uδ= +

Time-difference (tdEIT)

2 1T Tγ γ δγ= +2 1u u uω ω δ= +

Frequency-difference (fdEIT)

2 1ω ωγ γ δγ= +

( ) ( )( )( ) ( )

0 in on .

uu g

γγ

∇⋅ ∇ = Ω− ∇ ⋅ = ∂Ω

r rr r n

The relation between voltage u and admittivity γ is nonlinear since


EIT System Current Source

Digital waveform generation and DAC

Balanced current source using Howland circuit

Generalized impedance converter

Voltmeter Differential voltage

amplifier and ADC Digital phase-

sensitive demodulation using FPGA


Imaging Experiments


Regional Lung Ventilation

Sitting

R

X

Right Lateral Left Lateral

Sitting

RightLateral

LeftLateral


Stomach Filling and EmptyingFilling

Emptying

0s 35s 45s 56s 1m 3s 1m 33s 1m 48s 1m 54s20s (Intake)

15m 20m 22m 29s 25m 32m 30s 35m 50m 52m 29s


Applications of EIT

Time-difference imaging Pulmonary function Cardiac function Gastric emptying

Frequency-difference imaging Tumor Ischemic Stoke Hemorrhage


Commercial EIT SystemFrom http://www.drager.com

Electrode Belt Before Maneuver 10 Minutes After 4 Hours After


MREIT

Internal measurements

Non-invasive measurements

Non-contact measurements

Spatial information encoded in measured data

(Magnetic Resonance Electrical Impedance Tomography)

High-resolution conductivity imaging using MRI


( ) ( )( )( ) ( )

0 in on

uu g

σσ

∇⋅ ∇ = Ω− ∇ ⋅ = ∂Ω

r rr r n

( ) ( ) ( ) ( ) ( )uσ σ== − ∇J r r r r E r

( ) ( ) ( )03

' ''4 '

dµπ Ω

× −=

−∫

J r r rB r r

r r

1E2EΩ

∂Ω

I I

n

L− L+

a

(σ, u, J, B)

(g)

Probing by Injecting Current


Numerical Example using FEM

B. I. Lee, S. H. Oh, E. J. Woo, S. Y. Lee, M. H. Cho, O. Kwon, J. K. Seo, J. Lee, and W. S. Baek, “Three-dimensional forward solver and its performance analysis for MREIT using recessed electrodes," Phys. Med. Biol., vol. 48, 1972-1986, 2003.

σ

u

1E

2E

yx

yx

[S/m]

Bx

By

Bz

yx

yx

yx

Jx

Jy

Jz

yx

yx

yx

[mV]

[Tesla]

[Tesla]

[Tesla]

[mA/mm2]

[mA/mm2]

[mA/mm2]


B0

Electrode

Lead Wire

( )( , )( , )( , ) ( , ) x yz c j xm k yn kj B x y Tj x yS m n M x y e e e dxdyγδ∞ ∆ + ∆±±

−∞= ∫ ∫

MRI for MREIT

M. L. G. Joy, G. C. Scott, and R. M. Henkelman, “In vivo detection of applied electric currents bymagnetic 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 nonuniformcurrent density by magnetic resonance,” IEEE Trans. Med. Imag., vol. 10, no. 3, pp. 362-374, 1991.


Magnetic Flux Density (Bz) ImagingWe use both positive and negative injection currents.

Inverse Fourier Transform

Compute phase and unwrap phase

k-space data collection

Scaling and slice ordering


Agar PhantomPhantomMRI parameters:

TR/TE = 1400/60msFOV = 200mmMatrix size = 128 ×128Slice thickness/Gap = 3/0mmNumber of slices = 8Average = 2Current amplitude = 27mACurrent pulse width = 24msVoxel size(x,y,z) = 1.5625×1.5625×3mm3

Phantom:

Solution : 2S/m (NaCl=12.5g/l, CuSO4=2g/l)Object (agar) : 0.5S/m (NaCl=2g/l, CuSO4=2g/l, Agar=15g/l)


Agar PhantomWrapped

Phase ImageMR

Magnitude Image


Homogeneous Domain: Bz

Horizontal Injection Current Vertical Injection Current

-6

-4

-2

0

2

4

6

x 10-8

-6

-4

-2

0

2

4

6

x 10-8


Inhomogeneous Domain: Bz

Horizontal Injection Current Vertical Injection Current

-6

-4

-2

0

2

4

6

x 10-8

-6

-4

-2

0

2

4

6

x 10-8


Harmonic Bz Algorithm

Image DataModel(from Data)

where and

20 uµ σ∇ = − ∇ ×∇B0µ = ∇×J B 2

0 , ,zu uB

x y y xσ σµ

∂ ∂ ∂ ∂∇ = ⋅ − ∂ ∂ ∂ ∂

( ) ( ) ( )uσ= − ∇J r r r


CoReHA

Available from http://iirc.khu.ac.kr with manual and data sets

(Conductivity Reconstructor using Harmonic Algorithms)


CoReHA

iFFT Magnitude Image

Bz Image

K-space Data

| ⋅ |

∠

Phase Image

Unwrap

Coordinate Setup

Pre-processing


CoReHASegmentation Electrode Modeling Meshing and Modeling

HarmonicInpainting


Conductivity Image

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

Homogeneous Phantom(L2-error = 3.2%)

0

0.5

1

1.5

2

2.5

3

3.5

4

Agar Object Phantom(L2-error ~ 5%)

[S/m] [S/m]


Swine Leg

5

0

-5

[ Tesla ] ×10-8

MR Magnitude Image Bz Image forHorizontal Injection

Bz Image forVertical Injection


Swine Leg

0.6

0.5

0.4

0.3

0.2

0.1

0

[ S/m ]0.6

0.5

0.4

0.3

0.2

0.1

0

[ S/m ]

MR Magnitude Image Conductivity Image Color-coded Conductivity Image


Swine Leg

MR Magnitude Image

Conductivity Image

Color-coded Conductivity Image


Postmortem Canine Head

5

0

-5

[ Tesla ] ×10-8





MR Magnitude Image Conductivity Image

Skull

Temporalis fascia

Basisphenoid

Soft palate

Palatine tonsil

Masseter muscle

Lingualis proprius muscle

Gray matter

White matter

Temporalis muscle

Nasopharynx

Mandible

Digastricus muscle

Geniohyoideus muscle


MR Magnitude Image

Conductivity Image




In Vivo Canine Brain

MR Magnitude Image

Conductivity Image


5

0

-5

[ Tesla ] ×10-7

5

0

-5

[ Tesla ] ×10-7

E1+

E1-

E2+

E2-

Postmortem Canine Chest





Longissimusthoracis muscle

Spinal cord

Medias-tinum

Rightatrium

Right ventricle

Interventricular septum

Left ventricle

Esophagus

Body fluid accumulated in mediastinum

Body fluid in thoracic wall

Postmortem Canine Chest


MR Magnitude Image

Spinal cord

Medias-tinum Right

atrium

Right ventricle

Interventricular septum

Left ventricle

Esophagus

Trachea

Body fluid accumulated in mediastinum

Pleural fluid in pleural cavity

Longissimusthoracis muscle

Pneumonic Canine Chest

Normal Normal


MR Magnitude Image


Conductivity Image

Pneumonic Canine Chest


Spinal cord

Kidney

Liver

Spleen

Stomach

Large & small intestine

Peritoneal cavity


Postmortem Canine Abdomen



Spinal cord

Kidney

Gas trappedin intestine

Large & small intestine

Peritoneal cavity

Postmortem Canine Abdomen


Cortex

Medulla Renal pelvis

Urethra

Cortex

MedullaRenal pelvis

Urethra


Canine Kidney


MR Magnitude image Conductivity Image Color-coded Conductivity Image

SacrumMedial gluteus

medius

Rectum

Prostate glandIschium

Penis

Postmortem Canine Pelvis


MR Magnitude Image


Conductivity Image

Postmortem Canine Pelvis


Human Imaging


5

0

-5

[ Tesla ] ×10-8

5

0

-5

[ Tesla ] ×10-8

In Vivo Human Leg

E1+

E1-

E2+

E2-




Tibia

FibulaTibial nerveTibial artery & vein

Interosseousmembrane

Tendon

Calcaneal tendon

Tendon


In Vivo Human Leg


5

0

-5

[ Tesla ] ×10-8

5

0

-5

[ Tesla ] ×10-8

In Vivo Human Knee




Patellar ligament

Articular cartilage

Cruciate ligament

Tibial nerve

Gastrocnemius

Infrapatellar fat pad with synovial membrane

Medial femoral condyleLateral femoral condyle

Synovial capsule of knee joint


In Vivo Human Knee


MREIT Images


Signal in MREIT Phase Accumulation, Magnetic Flux Density, Bz

Imaging object• Shape and size• Conductivity distribution

Electrode configuration Amplitude of injection current, I

Current Injection Time, Tc Limited by TE and TR

Current injection during RF? Current injection during reading?

Typical Values using Spin Echo Pulse Sequence

( ) ( )2 c zT BγΦ =r r

6 2 82 41.065 10 [rad/s/T] 10 [s] 10 [T] 0.0082[rad] 1− −Φ = × × × × = ≈


Limitation in Injection Current Patient auxiliary current (IEC 601-1) : current flowing

in the patient in normal use between any patientconnection and all other patient connections and notintended to produce a physiological effect• 0 Hz – 0.1 Hz : 0.01 mArms

• 0.1 Hz – 1 kHz : 0.1 mArms

• 1 kHz – 100 kHz : 0.1 × f (in kHz) mArms

• Above 100 kHz : 10 mArms


Limitation in Injection Current Therapeutic current (IEC 601-2-10) is defined as

functional current from nerve or muscle stimulator• 0 Hz – 0.1 Hz : 80 mArms

• 0.1 Hz – 400 Hz : 50 mArms

• 400 Hz – 1500 Hz : 80 mArms

• Above 1500 Hz : 100 mArms

• For pulse duration < 0.1 s, pulse energy < 0.3 J

• Pulse voltage < 500 V

Diagnostic current in dentistry and ophthalmology(IEC 601-2-10)• 10 mArms


Limitation in Injection Current Threshold to stimulate a nerve with 20 µm diameter

(McRobbie and Foster, 1984)• 1 A/m2 below 1 kHz

• 2.5 mA through 5×5 cm2 uniform current density electrode

Conventional Electrode Uniform Current Density Electrode

(σ = 0.17 S/m) (σ = 0.17 S/m)


Noise in MREIT Random Noise in MR Phase Image

Noise Standard Deviation in Bz, • Current injection time, Tc• Magnitude image SNR, ΨM

Typical Values

Factors Affecting sBz• Performance of current source• Performance of MRI scanner including RF coils• Pulse sequence• MR imaging parameters

12zB

c M

sTγ

=Ψ

6 2

1 3.4 [nT]2 41.065 10 [rad/s/T] 10 [s] 500zBs

−= =

× × × ×


Applications Pathological changes related with conductivity

• Brain tumor• Breast tumor• Prostate tumor

Brain functions• Conductivity changes associated with neural activity• Conductivity changes related with brain injury, stroke,

epilepsy, tumor, and others Provide conductivity values to source imaging

problems in EEG, MEG, and ECG Planning and optimization of treatments using

electromagnetic energy Applications in biology and chemistry


Breast Model

Hydrogel : 0.17 S/mGlandular Tissue : 0.023 S/mSubcutaneous Fat : 0.019 S/mAnomaly : 0.0023 S/m

FOV : 135 mmSlice thickness : 4.2 mmImage size : 128 x 128Injected current : 0.7 or 1 mAAnomaly size : 15 mm

Glandular Tissue

Subcutaneous Fatty Tissue

Anomaly

HydrogelCarbon Electrode

Lead Wire

Voltage, u Current Density, Jx Current Density, Jy Voltage, u Current Density, Jx Current Density, Jy


Breast Simulation

Magnitude Bz - Horizontal ConductivityBz - Vertical

Magnitude Bz - Horizontal ConductivityBz - Vertical

1 mA Injection

0.7 mA Injection


Head Model• Height : 22.5 cm• Length: 18.8 cm• Width: 16.4 cm• Electrode size : 64 cm2

(8 × 8 cm2)


Head ModelModel Mesh

• Number of degrees of freedom = 2,709,374• Number of elements = 291,294


Head Model

Skin and electrodes (31,190 elements)

Skull (26,320 elements)

CSF (64,036 elements)

Brain (163,249 elements)Anomaly (580 elements) Ventricle (5,919 elements)


Simulation Settings

Skin

Skull

CSF

BrainAnomaly

Ventricle

• Hydrogel = 0.17 S/m• Skin = 0.17 S/m• Skull = 0.02 S/m• CSF = 0.91 S/m• Ventricle = 2.00 S/m• Brain = 0.09 S/m• Anomaly = 0.0945 S/m(5% contrast)

• FOV =200 mm• Slice thickness = 6.8 mm• Image size = 128• Current amplitude = 6.4 mA• Electrode size = 64 cm2

• Anomaly size: 15 mm

Conductivity

Imaging ParameterHydrogel


Horizontal Injection Current

Magnetic flux density, Bz

Current density, Jx Current density, Jy Voltage, u

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-7

-6

-5

-4

-3

-2

-1

0

-3

-2

-1

0

1

2

3

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-6

-4

-2

0

2

4

6

-1.5

-1

-0.5

0

0.5

1

1.5x 10

-8

-1.5

-1

-0.5

0

0.5

1

1.5x 10

-8


Vertical Injection Current

Magnetic flux density, Bz

Current density, Jx Current density, Jy Voltage, u

-6

-4

-2

0

2

4

6

0

1

2

3

4

5

6

7

8

9

10

0

0.5

1

1.5

2

-6

-4

-2

0

2

4

6

0

2

4

6

8

10

0

0.5

1

1.5

2

-1.5

-1

-0.5

0

0.5

1

1.5x 10

-8

-1.5

-1

-0.5

0

0.5

1

1.5x 10

-8


Without Noise

Magnitude Bz - Horizontal ConductivityBz - Vertical Conductivity

Without anomaly

With anomaly


With Noise

Magnitude Bz - Horizontal ConductivityBz - Vertical Conductivity

Without anomaly

With anomaly


Directions Maximize signal and minimize noise

• Optimize current source • Optimize electrode configuration• Optimize pulse sequence and imaging parameters• Increase current pulse width• Increase averaging (low temporal resolution)• Increase pixel size (low spatial resolution)• Improve RF coil• Use high-field high-performance MRI system

Reduced FOV and ROI imaging

Denoising techniques and hybrid algorithms

Reduce Imaging Current!


Multi-echo Pulse Sequence

Tc2

Tc1

Tc2

Tc1

Tc2

Tc2

Tc2

Tc1

90° 180° Echo 180° Echo 180° Echo

Spin echo

ICNE

Multi -echo

Injection current

Data acquisition

TE/2 TE 2TE 3TE

90° 180° Echo

90° 180° Echo

TE/2 TE

TE/2 TE


b-SSFP Pulse Sequence

RF pulse

GS

GP

GR

I

TRα < 900

( ) ( )( ) ( ) ( ) ( )( ) ( ) ( )( ) ( )

( ) ( ) ( ) ( )

1 1 2 2

1 2 2 1 2

0 1 2

0 1 2

2 2 20 12 2

( )

exp / , exp /

1 cos 1 cos cos cos

1 sin 1 cos /

1 sin sin /

1 sin, 1 2 cos

( , ) ( , ) x y

y

x

x y

j xm k yn kj

E TR T E TR T

D E E E E E

M M E E D

M M E E D

M EM x y M M E E

D

S m n M x y e e dxdyφ

α θ α θ

θ α θ

θ α θ

αθ

∞ − ∆ + ∆

−∞

= − = −

= − − − − −

= − −

= −

−= + = + −

= ∫ ∫


High-sensitivity RF Coils• Sodickson D K and Manning W J 1997 Simultaneous

acquisition of spatial harmonics (SMASH): fastimaging with radiofrequency coil arrays Magn. Reson.Med. 38 591-603

• Wiggins G C, Polimeni J R, Potthast A, Schmitt M,Alagappan V and Wald L L 2009 96-channel receive-only head coil for 3 Tesla: design optimization andevaluation Magn. Reson. Med. 62 754-62

• Mekle R, van der Zwaag W, Joosten A and Gruetter R2008 Comparison of three commercially availableradio frequency coils for human brain imaging at 3Tesla Magn. Reson. Mater. Phy. 21 53-61

• Hiratsuka Y, Miki H, Kikuchi K, Kiriyama I, Mochizuki T,Takahashi S and Sadamoto K 2007 Sensitivity of aneight-element phased array coil in 3 Tesla MR imaging:a basic analysis Magn. Reson. Med. Sci. 6 177-81www.medical.siemens.com

32 channel 64 channel


New Techniques in MRI•Scheffler K 2004 Fast frequency mapping with balanced SSFP: theory and applicationto proton-resonance frequency shift thermometry Magn. Reson. Med. 51 1205-11

•Klarhofer M, Barth M, Moser E 2002 Comparison of multi-echo spiral and echo planarimaging in functional MRI Magn. Reson. Imaging 20 356-64

•Ge Y, Korogi Y, Sugahara T, Shigematsu Y, Hirai T, Kitajima M, Liang L, Dai J andTakahashi M 2001 Comparison between EPI and HASTE for ultra-fast MR imaging ofthe human brain Neuroradiol. 43 1046-55

•Candes E, Romberg J and Tao T 2006 Robust uncertainty principles: exact signalreconstruction from highly incomplete frequency information IEEE Trans. Inf. Theory52 489-509

•Donoho D 2006 Compressed sensing IEEE Trans. Inf. Theory 52 1289-1306•Santos J M, Cunningham C H, Lusting M, Hargreaves B A, Hu B S, Nishimura D Gand Pauly J M 2006 Single breadth-hold whole-heart MRA using variable-densityspirals at 3T Mag. Res. Med. 55 371-379

•Block K T, Uecker M and Frahm J 2007 Under-sampled radial MRI with multiple coils:iterative image reconstruction using a total variation constraint Mag. Res. Med. 571086-1098

•Lusting M, Donoho D and Pauly J M 2007 Sparse MRI: the application of compressedsensing for rapid MR imaging Mag. Res. Med. 58 1182-1195


Towards Neuro-imaging

MRI-compatible EEG

MRI-compatible EIT

MREIT• Low-noise high-performance MRI system at 3 or 7 T• Uniform current density electrode, electrode configuration,

and low-noise current source• Sensitivity enhancement by improvements in RF coil and

pulse sequence • Fast imaging method• Denoising, image reconstruction, and anomaly detection

algorithms• Functional imaging protocol and statistical image analysis


Outlook: Multi-modal Approach

MRI-MREIT-EIT-

EEG

Multi-modal

Neuro-imaging

• MR image

• Surface voltage map

• Magnetic flux

density image

• Conductivity image

• Current density

image

• Current source

image

Surface voltage (EEG)- Endogenous- Spontaneous or evoked- 10-6 – 10-5 V

Surface voltage (EIT)- Exogenous- Spontaneous or evoked- 10-4 – 10-3 V

Internal magneticflux density (MREIT)- Exogenous- Spontaneous or evoked- 10-10 – 10-8 T

Geometry andother information (MRI)- Endogenous- Spontaneous or evoked


Collaborators at IIRC


Acknowledgement

National Research Foundation (NRF) of Korea• Impedance Imaging Research Center (IIRC)

• Ion Conduction Imaging Group

Kyung Hee University

Researchers at IIRC• Mathematicians

• Engineers

• Biologists and clinicians

International Collaborators


Thank you for your attention.

Documents

Magnetic Resonance Electrical Impedance Tomography (MREIT)web.yonsei.ac.kr/nipi/lectureNote/MREIT(ISMRM2011) by Woo.pdf · IIRC, KHU Magnetic Resonance Electrical Impedance Tomography