DataCollection in MREIT€¦ · IIRC, Kyung Hee Univ. May, 2014 19 Signal and Noise in MREIT...
Transcript of DataCollection in MREIT€¦ · IIRC, Kyung Hee Univ. May, 2014 19 Signal and Noise in MREIT...
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Data Collection in MREIT
Eung Je Woo
Department of Biomedical Engineering
Kyung Hee University
http://iirc.khu.ac.kr
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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
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EOD