DataCollection in MREIT€¦ · IIRC, Kyung Hee Univ. May, 2014 19 Signal and Noise in MREIT...

Data Collection in MREIT

Eung Je Woo

Department of Biomedical Engineering

Kyung Hee University

[email protected]

http://iirc.khu.ac.kr

IIRC, Kyung Hee Univ. May, 2014

2

Bioelectromagnetism at Low Frequency (Exogenous)

, 4′, ′| ′| ′

⋅ , , 0inΩ, , ⋅ on Ω

Admittivity

Voltage

, , ,

Magnetic Flux Density

Current Density

Injection Current (Exogenous)


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MREIT( ) ( ) ( )V J r r r 0 3

'( ) ( ') '4 '

dv

r rB r J rr r

V J B ( ) ( ) 0V r r

on nV Jn

J BJ‐ Algorithm

0

1( ) ( )

J r B r

BzBz‐ Algorithm

J BzBz‐J AlgorithmJ‐ Algorithm


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Magnetic Field Imaging using MRI

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 dxdy

Joy et al., Mag. Reson. Imag., 1989

Scott et al., IEEE Trans. Med. Imag., 1991


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Spin Echo

RF

Gp

TE

TE/2 TE/2

t

t

t

90o180o

t

Spin Echo

Gr

Gs

tITc2

Tc1


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Phase Accumulation in Spin Echo

t2t

FIDRF echo signal or spin echo (SE)

t0 t4t3

t0 t1 t4t2 t3

RF 90 RF 180

t1

TE/2 TE/2TE

Extra phase by BzTc1 Extra phase by Bz Tc2


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Gradient Echo

ITc

RF

Gs

Gr

Gp

°

t

t

t

t

GE signal

t


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Phase Accumulation in Gradient EchoDephasing gradient pulse

Rephasing gradient pulse

t

FID signal

Rephased or echo signal (gradient echo)

t0 t2 t4t1 t3

t0 t1 t4t2 t3Extra phase by BzTc


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Magnetic Flux DensityWe use both positive and negative injection currents.

Inverse Fourier Transform

Compute phase and unwrap phase

k‐space data collection

Scaling and slice ordering


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CDI by Subject Rotation

),,(1),,(0

zyxzyx BJ

B0

Transversal ImagingSlice for Bz

Three Coronal ImagingSlice for Bx

Three Sagittal ImagingSlice for By

( , ) ( )( , )( , ) ( , ) q c x yj B x y T j xm k yn kj x yqS m n M x y e e e dxdy

zyx aaay

Bxx

Byx

Bzz

Bxz

Byy

Bz0

1


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Magnetic Field Imaging using MRIWrapped Phase Image

MRMagnitude Image


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Magnetic Flux Density ImageHorizontal Injection Current Vertical Injection Current

-6

-4

-2

0

2

4

6

x 10-8

[T]

2 0zB 2 0zB

2 0zB 2 0zB

20 u B

0 J B

u J


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MREIT (Magnetic Resonance Electrical Impedance Tomography)

Image DataModel(from Data)

where and

20 u B0 J B

20 , ,z

u uBx y y x

u J r r r


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CoReHA (Conductivity Reconstructor using Harmonic Algorithms)

http://iirc.khu.ac.kr


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CoReHA (Conductivity Reconstructor using Harmonic Algorithms)Segmentation Electrode Modeling Meshing and Modeling

HarmonicInpainting


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MREIT Image

1.4 mm 1.8 mm 2.2 mm

1.7 mm 1.4 mm 1.4 mm

1.4 mm

Canine Head Canine Chest Canine Abdomen

Canine Pelvis Human Leg Human Knee

Canine Head


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MRI vs. Conductivity Image

Right atrioventricularvalve

Right ventricle

Ventricular septum

Left ventricle

Left atrioventricularvalve

Cortex

Medulla Renal pelvis

Ureter Cortex

MedullaRenal pelvis

Ureter

Peripheral zone

Urethral crest

Central zone

Fibrous connective tissue

a

Heart

Kidney

Prostate


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MRI vs. Conductivity Image (Canine Pelvis)

MR Magnitude Image

Conductivity Image

Color‐coded Conductivity Image


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Signal and Noise in MREIT

• Strength and Distribution of Signal Bz• Imaging object

• Shape and size• Conductivity distribution

• Electrode configuration• Amplitude of injection current, I

• Noise in Bz• Magnitude image SNR

• Voxel size and TR/TE• Main magnetic field strength

• Duration of injection current, Tc• Other MR imaging parameters and pulse sequence


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Pulse Sequences

RF

SliceSelection

PhaseEncoding

Reading

CurrentI

-I

Tc

I

-I

0.5Tc 0.5Tc

Spin Echo (SE) Gradient Echo (GE)


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Noise Estimate in MREIT

M

Z

M ZRe[Z]

ReIm

Im[Z]

O

O Add noise:


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Noise Measurement

HomogeneousConductivity

and


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Measured Noise in Bz

-0.02 -0.01 0 0.01 0.020

20

40

60

80

100

[T/m2]

3T

-0.02 -0.01 0 0.01 0.020

20

40

60

80

100

[T/m2]

11T

Field Strength [T] 3 11NEX 1 4 1 4

11.8 22.2 59.6 123

[nT] 13.9 7.54 2.73 1.32

[nT] 15.0 6.72 2.91 1.35

• Conductivity = 0.625 S/m

• Voxel size = 111 mm3

• Injection current = 10 mA

• Pulse width = 16 ms

DataCollection in MREIT€¦ · IIRC, Kyung Hee Univ. May, 2014 19 Signal and Noise in MREIT...

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