3/13/2010

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

18 YO male with low back pain -

Fibrous dysplasia
Courtesy of Dr. Boaz Karmazyn

T1 STIR
Chen Lin, PhD 3/2010

1
 3/13/2010

15 yo w/ hip pain and decreased ROM

Normal bone marrow Leukemia

Courtesy of Dr. Boaz Karmazyn

T1

STIR

Chen Lin, PhD 3/2010

Fat Saturation

T1w T1w + FS

Chen Lin, PhD 3/2010

Chemical Shift Artifact

rBW = 125Hz rBW = 490Hz

Chen Lin, PhD 3/2010

2
 3/13/2010

Artifacts in EPI

N/2 Ghosting
Distortion
(Expansion)

Chemical shift

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:
Field Strength F/W Separation
1.5T 220 Hz
3.0T 440 Hz
• T1 and T2 relaxation time:
Field Strength T1 Relaxation Time
1.5T 220 ms
3.0T 260 ms
• J-coupling

Chen Lin, PhD 3/2010

3
 3/13/2010

Chemical Shift Selective Saturation

• Spectrally selective excitation (Narrow BW
excitation with no gradient applied) + spoiling.

University Munich (LMU),

• Suppress signal within certain resonance
frequency range. i.e. fat.

T1 FLASH, FatSat, Post T2 TSE, FatSat

Chen Lin, PhD 3/2010

Shoulder w/o & w. Fat Suppression

PD PD + Fat Sat

Chen Lin, PhD 3/2010

Strong versus Weak FatSat for Ortho

Optimized Flip Angle Fixed Flip Angle

Chen Lin, PhD 3/2010

4
 3/13/2010

Quick FatSat for Breast Imaging

T1 VIBE Dynamic T1 + Fat Sat

• Interleaved, 1 / 40 k-space lines.

• Use Quick FatSat to maintain temporal
resolution.
Chen Lin, PhD 3/2010

In-homogeneous B0 field

Chen Lin, PhD 3/2010

Better Shim Capability

Gradient shim High order shim

Chen Lin, PhD 3/2010

5
 3/13/2010

Adjust Shim Volume

3D Shim Volume

3D T2 SPACE w. FatSat @ 3T

Chen Lin, PhD 3/2010

Optimizing Center Frequency

Multiple scan of 20sec each

100 Hz 150 Hz 200 Hz 250 Hz

Chen Lin, PhD 3/2010

Full Scan with Offset of 200Hz

Chen Lin, PhD 3/2010

6
 3/13/2010

Adjust/Confirm Center Frequency

Chen Lin, PhD 3/2010

Composite RF Pulse
• Concatenation of sub pulses to improve performance
(i.e. insensitive to B0 and B1 inhomogeneity)
90x 90y 90x
• Composite ChemSat Pulses:
 CHEmical Shift Selective
(CHESS)
 Binomial Pulse (ProSat, WE) Gs Gs Gs

 Spectral Spatial Pulse (SpSp)

 Band Selective Inversion
with Gradient dephasing
(BASING)
 MEGA, MELV Chen Lin, PhD 3/2010

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

Chen Lin, PhD 3/2010

7
 3/13/2010

1-1 Binomial for Water Only

45° 45°

t = 1/2*f

time

Bo Bo Bo Bo

Chen Lin, PhD 3/2010

1-1 Binomial for Fat Only

45° t = 1/2*f

time
45°

Bo Bo Bo Bo

Chen Lin, PhD 3/2010

ProSet Examples

1 1 1 2 1 1 3 3 1

• Limited slice thickness

• Lengthy pulse
Chen Lin, PhD 3/2010

8
 3/13/2010

WE versus FatSat for Foot

Water Excitation Conventional Fat Sat

Chen Lin, PhD 3/2010

Spectral Spatial (SpSp) pulse

Amplitude
Modulation

RF pulses

Gradient
Waveform

Chen Lin, PhD 3/2010

Excitation Profile of SpSp

Zur Y., MRM, 43, 410, 2000

Chen Lin, PhD 3/2010

9
 3/13/2010

SpSp Considerations

Without Fat With Fat

Suppression Suppression

 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

STIR, and compare with FLAIR

STIR/TRIM : Short Tau Inversion Recovery,
FLAIR: FLuid Attenuated Inversion Recovery, “Dark Fluid”

Signal
Fat signal

Fluid signal Time

Inversion TInull(Fat) TInull (Water)

RF Pulse
Chen Lin, PhD 3/2010

Interleave of Inversion & Acquisition

IR1 IR2 IR3 IR4 IR5

ACQ1 ACQ2 ACQ3 ACQ4 ACQ5

STIR
TI

IR1 IR2 IR3 IR4 IR5

ACQ1 ACQ2 ACQ3 ACQ4 ACQ5

FLAIR
TI

Chen Lin, PhD 3/2010

10
 3/13/2010

Dependence on Flip Angle and TR

As the inversion flip angle or TR decreases:
0.15
180
150
120

Relative |Mz(t)|
0.1

0.05

0
200 250 300

T1 (ms)

TINull decreases Suppression less selective

Chen Lin, PhD 3/2010

Multifocal MRSA Osteomyelitis

Courtesy of Dr. Boaz Karmazyn of IUSM

Chen Lin, PhD 3/2010

STIR versus FATSAT in the Presence of

Field Inhomogeneity

STIR T1 TSE with FATSAT

Chen Lin, PhD 3/2010

11
 3/13/2010

More about STIR

• In-sensitive to B0 • Lower SNR
inhomogeneity – improved with shorter
– More reliable than TE (17-48 msec )
FATSAT for large FOV and • Bad idea with Gd
off-center (shoulder)
– shorter post-contrast
– works at lower field tumor T1
strengths
• Red marrow signal can
• High visibility for fluid obscure subtle edema
– long T1 bright on STIR – use TE=45-48+ to
– long T2 bright on STIR, suppress marrow
given long enough TE

Chen Lin, PhD 3/2010

Modified STIR for MSK

Kijowski, R. et al. Am. J. Roentgenol.
2005;185:371-378

STIR Modified STIR

• TE=50-100; TI=110-120 @ 1.5T
• Improved SNR and maintain fluid sensitivity
Chen Lin, PhD 3/2010

Water Saturation plus STIR

Water Fat Silicone

Freq

220Hz 320Hz

Silicone Breast Implants

Chen Lin, PhD 3/2010

12
 3/13/2010

SPIR
Spectral Water signal
Selective
IR Pulse Fat signal
Excitation Pulse

Fat null

• SPectral selective Inversion Recovery

• Frequency selective inversion pulse (1000 – 1100) to
invert fat only.
• SNR of water is perserved.
Chen Lin, PhD 3/2010

B1 Non-uniformity
• Inherent in the scanner
– Design and tuning of
body coil
• 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
Chen Lin, PhD 3/2010

In-homogeneous B1 field

Chen Lin, PhD 3/2010

13
 3/13/2010

SPAIR , ASPIR
Spectral Water signal
Selective
Adiabatic Fat signal
IR Pulse
Excitation Pulse

Fat null

• 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

Conventional vs Adiabatic Inversion

Z Z Z Z Z

M
M
M
Y Y Y Y Y
B1 B1 B1 B1 B1
M M
X X X X X
Z Z Z Z Z

M
M
B1 M
B1
Y Y Y Y Y
B1 B1 M
B1 M
X X X X X
Chen Lin, PhD 3/2010

B1 Sensitivity
Z Z Z Z Z

M
M
M M M
Y Y Y Y Y
B1 B1 B1 B1 B1
X X X X X
Z Z Z Z Z

M
M
B1 M
B1
Y Y Y Y Y
B1 B1 M
B1 M
X X X X X

Chen Lin, PhD 3/2010

14
 3/13/2010

SPAIR versus SPIR

T2 TSE w. SPAIR T2 TSE w. SPIR

Chen Lin, PhD 3/2010

C-Spine with SPAIR

TSE w. SPAIR
Chen Lin, PhD 3/2010

Breast DCE with SPAIR @ 3T

VIBE with SPAIR VIBE with FATSAT

Chen Lin, PhD 3/2010

15
 3/13/2010

Abdominal Applications

DW SS-EPI @ b=50 w. SPAIR HASTE w. SPAIR

Chen Lin, PhD 3/2010

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

TE: 0 ms 2.25 ms 4.5 ms @ 1.5T

Water

Fat

ST (TEOut) = SW - SF(TEOut) ST (TEIn) = SW + SF(TEIn)

SW = [ST(TEIn) + ST(TEOut)]/2 ; SF(TEOut) = [ST(TEIn) - ST(TEOut)]/2

Chen Lin, PhD 3/2010

16
 3/13/2010

17 yo boy with Hodgkin's disease,

treated for right knee metastasis

Courtesy of Dr. Boaz Karmazyn

T2 FS T1 In Phase Op Phase

Chen Lin, PhD 3/2010

Two and Three Point DIXON

a(qn) a(qn+1)
TR

Gslice

Gread

Gphase

OUT IN OUT

Chen Lin, PhD 3/2010

Two-point DIXON Example

TE = 2.4ms TE = 4.8ms

Water-only Fat-only
Chen Lin, PhD 3/2010

17
 3/13/2010

3PT DIXON Example

TE = 2.4ms TE = 4.8ms TE = 9.5ms

Water-only Fat-only T2*

Chen Lin, PhD 3/2010

Breast Fat Suppression @ 3.0T

Chen Lin, PhD 3/2010

Cor T1 of Pelvis with TSE DIXON

TSE DIXON TSE DIXON

In-Phase Op-Phase

TSE DIXON TSE DIXON

Water-only Fat-only

Chen Lin, PhD 3/2010

18
 3/13/2010

TSE DIXON of Ankle with Metal

TSE DIXON TSE DIXON

Water-only

TSE TSE FatSat

Chen Lin, PhD 3/2010

Water + Lipid Suppression in MRS

Chen Lin, PhD 3/2010

Very Selective Saturation (VSS) Pulse

1 Mz/Mo

VSS 0.8

0.6
Conventional
OVS 0.4

0.2

0
-20 -15 -10 -5 0 5 10 15 20
Z (mm)
Chen Lin, PhD 3/2010

19
 3/13/2010

Shaping the PRESS box with VSS bands

Chen Lin, PhD 3/2010

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

Benefit of VSS Sat. Band

Cit
Cho/Cr

lipid
Cit
Cho/Cr
3 cm thick Lipids

Edge of
VSS Band

Chen Lin, PhD 3/2010

20
 3/13/2010

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

21