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CHAP 8 Image quality, SNR, CNR
– Introduction
– SNR
– CNR
– K-space filling strategies
CHAP 9 Off-Resonance effects
– Magnetic Susceptibility
– Implication for Imaging
– Water-Fat shift
CHAP 8 Image quality, SNR, CNR
– Introduction
– SNR
– CNR
– K-space filling strategies
CHAP 9 Off-Resonance effects
– Magnetic Susceptibility
– Implication for Imaging
– Water-Fat shift
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Image quality: The art of “trade-off”
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SNR definition
SNR in MRI
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Practical SNR measurement
CNR (Contrast to Noise Ratio)
Rel
SI,
rel
CN
R
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CHAP 8 Image quality, SNR, CNR
– Introduction
– SNR
– CNR
– K-space filling strategies
CHAP 9 Off-Resonance effects
– Magnetic Susceptibility
– Implication for Imaging
– Water-Fat shift
kx
ky
p1
p*1
p2
p*2
Partial k-space sampling
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Partial Echo acquisition
TE
Tacq
TE
Tacq
Gx
Partial Echo: pulse sequence
diagram
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Acceleration
Acceleration
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Scan Percentage
Scan Percentage
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Scan Percentage
Scan Percentage
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Scan Percentage
Scan Percentage
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Scan Percentage
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Scan Percentage
Scan Percentage
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Scan Percentage
Scan Percentage
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Scan Percentage
Scan Percentage
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Scan Percentage
Scan Percentage
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Scan Percentage
Scan Percentage
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Acceleration
Partial Fourier (half scan)
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Partial Fourier (half scan)
Partial Fourier (half scan)
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Partial Fourier (half scan)
Partial Fourier (half scan)
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Partial Fourier (half scan)
Partial Fourier (half scan)
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Partial Fourier (half scan)
Partial Fourier (half scan)
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Rectangular FOV
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Rectangular FOV
Rectangular FOV
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Rectangular FOV
Rectangular FOV
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Rectangular FOV
Rectangular FOV
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Rectangular FOV
Matrix size
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Matrix size
Matrix size
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FOV Size
FOV Size
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FOV Size
FOV Size
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FOV Size
FOV Size
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FOV Size
CHAP 8 Image quality, SNR, CNR
– Introduction
– SNR
– CNR
– K-space filling strategies
CHAP 9 Off-Resonance effects
– Magnetic Susceptibility
– Implication for Imaging
– Water-Fat shift
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Magnetic properties of matter
placed in a magnetic field
Magnetic Susceptibility
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CHAP 8 Image quality, SNR, CNR
– Introduction
– SNR
– CNR
– K-space filling strategies
CHAP 9 Off-Resonance effects
– Magnetic Susceptibility
– Implication for Imaging
– Water-Fat shift
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In practice…
B pixel
B
pixel
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Intravoxel dephasing
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Bz
Geometric distortion
Susceptibility artefact
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x
B0 homogeneity in the bore
CHAP 8 Image quality, SNR, CNR
– Introduction
– SNR
– CNR
– K-space filling strategies
CHAP 9 Off-Resonance effects
– Magnetic Susceptibility
– Implication for Imaging
– Water-Fat shift
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H2O and Fat
Water-Fat-Shift
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”in-phase / out-of-phase” evolution
GRE sequences
In-phase / out-of-phase
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In-phase / out-of-phase images
Water-fat shift artefact
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Field strength and water-fat-shift
Fat and water image: Ankle
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