How to Get Rid of Fat Comparison of Fat Suppression ...mri/seminars/slides/fat suppression by Chen Lin.pdf · Comparison of Fat Suppression Techniques in Clinical MRI ... –Composite

3/13/2010

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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

3/13/2010

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T1

STIR

Normal bone marrow Leukemia

15 yo w/ hip pain and decreased ROM

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Fat Saturation

T1w T1w + FS


Chemical Shift Artifact


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)


MRI Properties of Fat

• Chemical Shift:

• T1 and T2 relaxation time:

• J-coupling

Field Strength F/W Separation1.5T 220 Hz3.0T 440 Hz


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.


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


Strong versus Weak FatSat for Ortho


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


In-homogeneous B0 field


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


Optimizing Center Frequency

Multiple scan of 20sec each


100 Hz 150 Hz 200 Hz 250 Hz

Full Scan with Offset of 200Hz


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Adjust/Confirm Center Frequency


Composite RF Pulse

• Concatenation of sub pulses to improve performance (i.e. insensitive to B0 and B1 inhomogeneity)


• 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


Bo BoBoBo

45°

1-1 Binomial for Fat Only

45°

time

t = 1/2*f


Bo BoBoBo

45°

ProSet Examples

• Limited slice thickness

• Lengthy pulse


1 1 1 2 1 1 3 3 1

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WE versus FatSat for Foot


Water Excitation Conventional Fat Sat

Spectral Spatial (SpSp) pulse


RF pulses

Gradient Waveform

Amplitude Modulation

Excitation Profile of SpSp


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.


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


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


TINull decreases Suppression less selective

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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


Kijo

wsk

i, R

. et

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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


Water Saturation plus STIR

Water Fat Silicone

Freq


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.


Fat null

Fat signal

Water signalSpectral Selective IR Pulse

Excitation Pulse

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

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.


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


B1 SensitivityZ

Y

X

M

B1

Z

Y

X

M

B1

Z

X

M

B1

Y

Z

Y

X

M

B1

Z

Y

X

M

B1

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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SPAIR versus SPIR

T2 TSE w. SPAIR


T2 TSE w. SPIR


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


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.


In/Op Phases and DIXON, IDEAL


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

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of

Dr.

Bo

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Two and Three Point DIXON

Gslice

Gphase

Gread

TRa(qn) a(qn+1)


OUT IN OUT

Two-point DIXON Example


TE = 2.4ms TE = 4.8ms

Water-only Fat-only

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3PT DIXON Example


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

Water-only Fat-only T2*

Breast Fat Suppression @ 3.0T


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


TSE DIXON Water-only

TSE FatSat

TSE DIXON

TSE

Water + Lipid Suppression in MRS



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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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



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.


Thank You !

www.indiana.edu/~mri

How to Get Rid of Fat Comparison of Fat Suppression ...mri/seminars/slides/fat suppression by Chen Lin.pdf · Comparison of Fat Suppression Techniques in Clinical MRI ... –Composite

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