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How to Get Rid of Fat –Comparison of Fat Suppression
Techniques in Clinical MRI
Chen Lin, PhD
Indiana University School of Medicine & Clarian Health Partners
Declaration of Conflict of Interest or Relationship
Research support from Siemens Healthcare
STIRT1
18 YO male with low back pain -Fibrous dysplasia
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Chen Lin, PhD 3/2010
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T1
STIR
Normal bone marrow Leukemia
15 yo w/ hip pain and decreased ROM
Co
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of
Dr.
Bo
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arm
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Chen Lin, PhD 3/2010
Fat Saturation
T1w T1w + FS
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Chemical Shift Artifact
Chen Lin, PhD 3/2010
rBW = 125Hz rBW = 490Hz
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N/2 Ghosting
Chemical shift
Distortion (Expansion)
Artifacts in EPI
More severe at higher field strength
Fat Suppression Options
• Based on chemical shift difference (Freq. Selective)
– Conventional FatSat (FS) or ChemSat (CS)
– Composite RF pulse (ProSat, WE, SpSp, CHESS, etc.)
– In-phase / Op-phase and DIXON/IDEAL
• Based on T1 relaxation difference
– STIR
• Hybrid
– SPIR and SPAIR
• Based on spatial distribution (Spatial sat. band)
• Subtraction (For dynamic imaging)
Chen Lin, PhD 3/2010
MRI Properties of Fat
• Chemical Shift:
• T1 and T2 relaxation time:
• J-coupling
Field Strength F/W Separation1.5T 220 Hz3.0T 440 Hz
Chen Lin, PhD 3/2010
Field Strength T1 Relaxation Time1.5T 220 ms3.0T 260 ms
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Chemical Shift Selective Saturation
• Spectrally selective excitation (Narrow BW excitation with no gradient applied) + spoiling.
• Suppress signal within certain resonance frequency range. i.e. fat.
Chen Lin, PhD 3/2010
T1 FLASH, FatSat, Post T2 TSE, FatSat
Un
ive
rsit
y M
un
ich
(LM
U),
Shoulder w/o & w. Fat Suppression
PD PD + Fat Sat
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Strong versus Weak FatSat for Ortho
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Fixed Flip AngleOptimized Flip Angle
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Quick FatSat for Breast Imaging
• Interleaved, 1 / 40 k-space lines.
• Use Quick FatSat to maintain temporal resolution.
T1 VIBE Dynamic T1 + Fat Sat
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In-homogeneous B0 field
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Better Shim Capability
Gradient shim High order shimChen Lin, PhD 3/2010
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Adjust Shim Volume
3D T2 SPACE w. FatSat @ 3T
3D Shim Volume
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Optimizing Center Frequency
Multiple scan of 20sec each
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100 Hz 150 Hz 200 Hz 250 Hz
Full Scan with Offset of 200Hz
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Adjust/Confirm Center Frequency
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Composite RF Pulse
• Concatenation of sub pulses to improve performance (i.e. insensitive to B0 and B1 inhomogeneity)
Chen Lin, PhD 3/2010
• Composite ChemSat Pulses:
CHEmical Shift Selective (CHESS)
Binomial Pulse (ProSat, WE)
Spectral Spatial Pulse (SpSp)
Band Selective Inversion with Gradient dephasing (BASING)
MEGA, MELV
90x 90y 90x
Gs Gs Gs
ProSet
• Principle of Selective excitation technique
• A train of RF pulses with pre-defined amplitude ratios and spacing
• Produce water-only or fat-only excitation
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1-1 Binomial for Water Only45°
time
t = 1/2*f
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Bo BoBoBo
45°
1-1 Binomial for Fat Only
45°
time
t = 1/2*f
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Bo BoBoBo
45°
ProSet Examples
• Limited slice thickness
• Lengthy pulse
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1 1 1 2 1 1 3 3 1
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WE versus FatSat for Foot
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Water Excitation Conventional Fat Sat
Spectral Spatial (SpSp) pulse
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RF pulses
Gradient Waveform
Amplitude Modulation
Excitation Profile of SpSp
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Zur
Y., M
RM
, 43,
410
, 200
0
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SpSp Considerations
Less spatially selective with short sub-pulses.
More sensitive to B0 inhomogeneity with fewer sub-pulses.
Require accurate alignment of RF and gradient waveforms.
Chen Lin, PhD 3/2010
With Fat Suppression
Without Fat Suppression
STIR, and compare with FLAIR
STIR/TRIM : Short Tau Inversion Recovery,
FLAIR: FLuid Attenuated Inversion Recovery, “Dark Fluid”
TInull (Water)
Fat signal
Fluid signal
Inversion RF Pulse
Signal
TInull(Fat)
Time
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Interleave of Inversion & Acquisition
ACQ1
IR1
TI
ACQ1
IR1
ACQ2
IR2
ACQ3
IR3
ACQ4
IR4
ACQ5
IR5
TI
IR2 IR3 IR4 IR5
ACQ2 ACQ3 ACQ4 ACQ5
STIR
FLAIR
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Dependence on Flip Angle and TR
As the inversion flip angle or TR decreases:
0
0.05
0.1
0.15
200 250 300
T1 (ms)
Rel
ativ
e |M
z(t)
|
180150120
Chen Lin, PhD 3/2010
TINull decreases Suppression less selective
Multifocal MRSA Osteomyelitis
Chen Lin, PhD 3/2010
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STIR versus FATSAT in the Presence of Field Inhomogeneity
STIR T1 TSE with FATSAT
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More about STIR
• In-sensitive to B0
inhomogeneity
– More reliable than FATSAT for large FOV and off-center (shoulder)
– works at lower field strengths
• High visibility for fluid
– long T1 bright on STIR
– long T2 bright on STIR, given long enough TE
• Lower SNR
– improved with shorter TE (17-48 msec )
• Bad idea with Gd
– shorter post-contrast tumor T1
• Red marrow signal can obscure subtle edema
– use TE=45-48+ to suppress marrow
Chen Lin, PhD 3/2010
Kijo
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. et
al. A
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Modified STIR for MSK
• TE=50-100; TI=110-120 @ 1.5T
• Improved SNR and maintain fluid sensitivity
STIR Modified STIR
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Water Saturation plus STIR
Water Fat Silicone
Freq
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Silicone Breast Implants
220Hz 320Hz
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SPIR
• SPectral selective Inversion Recovery
• Frequency selective inversion pulse (1000 – 1100) to invert fat only.
• SNR of water is perserved.
Chen Lin, PhD 3/2010
Fat null
Fat signal
Water signalSpectral Selective IR Pulse
Excitation Pulse
B1 Non-uniformity
• Inherent in the scanner
– Design and tuning of body coil
Chen Lin, PhD 3/2010
• Caused by patient
– RF shielding and dielectric effect
– Often seen in Torso and Pelvis
– More prominent at high field such as 3.0T
Consequence:
Receiving -> variation of signal intensity
Transmitting -> variation of flip angle
In-homogeneous B1 field
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SPAIR , ASPIR
• SPectral Attenuated Inversion Recovery
• SPectral-selective Adiabatic Inversion Recovery
• Adiabatic SPectral-selective Inversion Recovery
• Uses an adiabatic frequency selective inversion pulse.
Chen Lin, PhD 3/2010
Fat null
Fat signal
Water signalSpectral Selective AdiabaticIR Pulse
Excitation Pulse
Conventional vs Adiabatic InversionZ
Y
X
M
B1
Z
Y
X
M
B1
Z
Y
X
M
B1
Z
Y
X
MB1
Z
Y
X
MB1
Z
Y
X
M
B1
Z
Y
X
M
B1
Z
Y
X
M
B1
Z
Y
X
MB1
Z
Y
X
MB1
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B1 SensitivityZ
Y
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M
B1
Z
Y
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M
B1
Z
X
M
B1
Y
Z
Y
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M
B1
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Y
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M
B1
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M
B1
Z
Y
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M
B1
Z
Y
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M
B1
Z
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MB1
Z
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MB1
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SPAIR versus SPIR
T2 TSE w. SPAIR
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T2 TSE w. SPIR
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C-Spine with SPAIR
TSE w. SPAIR
Breast DCE with SPAIR @ 3T
VIBE with SPAIR VIBE with FATSAT
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Abdominal Applications
DW SS-EPI @ b=50 w. SPAIR HASTE w. SPAIR
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SPAIR, ASPIR
• STIR ‘like’ contrast, but for fat only.
• Insensitivity to B1 inhomogeneity (better for 3.0T).
• Takes longer time than FatSat and SPIR (compensate by applying less frequently).
• SPAIR delay time can be set on Phillips.
Chen Lin, PhD 3/2010
In/Op Phases and DIXON, IDEAL
Chen Lin, PhD 3/2010
2.25 ms 4.5 msTE: 0 ms @ 1.5T
Water
Fat
SW = [ST(TEIn) + ST(TEOut)]/2 ; SF(TEOut) = [ST(TEIn) - ST(TEOut)]/2
ST (TEIn) = SW + SF(TEIn)ST (TEOut) = SW - SF(TEOut)
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T2 FS T1 In Phase Op Phase
17 yo boy with Hodgkin's disease,treated for right knee metastasis
Co
urt
esy
of
Dr.
Bo
az K
arm
azyn
Chen Lin, PhD 3/2010
Two and Three Point DIXON
Gslice
Gphase
Gread
TRa(qn) a(qn+1)
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OUT IN OUT
Two-point DIXON Example
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TE = 2.4ms TE = 4.8ms
Water-only Fat-only
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3PT DIXON Example
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TE = 2.4ms TE = 4.8ms TE = 9.5ms
Water-only Fat-only T2*
Breast Fat Suppression @ 3.0T
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Cor T1 of Pelvis with TSE DIXON
TSE DIXON Water-only
TSE DIXONIn-Phase
TSE DIXONOp-Phase
TSE DIXON Fat-only
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TSE DIXON of Ankle with Metal
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TSE DIXON Water-only
TSE FatSat
TSE DIXON
TSE
Water + Lipid Suppression in MRS
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Chen Lin, PhD 3/2010
Very Selective Saturation (VSS) Pulse
0-20 -15 -10 -5 0 5 10 15 20
Z (mm)
0.2
0.4
0.6
0.8
1 Mz/Mo
Conventional
OVS
VSS
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Chen Lin, PhD 3/2010
Shaping the PRESS box with VSS bands
Shaping the PRESS Box with VSS
• 6 default ROI-edge bands controlled by UserCV
• 4 - 6 additional GRx bands
• Progressive flip angles
Chen Lin, PhD 3/2010
Chen Lin, PhD 3/2010
Benefit of VSS Sat. Band
Lipids
Edge of
VSS Band
3 cm thick
Cit
Cho/Cr
Cit
Cho/Cr
lipid
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Summary
• There are MANY options to perform fat suppression in MRI.
• Each has its own pros and cons.
• Need to understand their potentials and pitfalls when selecting the best fat suppression options according to the application.
Chen Lin, PhD 3/2010
Thank You !
www.indiana.edu/~mri