3/12/2010

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MRI Techniques for Neuro and MSK Imaging

Chen Lin, PhD

Indiana University School of Medicine & Clarian Health Partners

Declaration of Conflict of Interest or Relationship

Research support from Siemens Healthcare

Chen Lin, PhD 3/2010

Typical Neuro Protocols

Routine Brain

• LOC 3PL

• SAG T1 SE

• SAG T2 FLAIR

• AX T2 FLAIR

• AX T1 SE

• AX T2 TSE FS +C

• AX DW EPI +C

• AX T1 3D IRSPGR +C

• COR T1 SE FS +C

• SAG T1 SE +C OPT

• AX T1 SE +C OPT

Routine Spine

• LOC 3PL

• SAG COR LOC

• SAG T1 TSE

• SAG STIR

• AX T1 TSE

• SAG T2 TSE +C (3D)

• Sag T1 TSE FS +C

• AX T1 TSE +C

Chen Lin PhD 3/2010

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Typical Ortho Protocols

Routine Knee

• AX LOC

• SAG COR LOC

• AX T2 TSE FS

• AX GRE

• SAG PD TSE

• SAG T2 TSE

• COR PD TSE

• COR STIR

• OCOR T2 ACL

• OSAG T2 ACL

Routine Shoulder

• AX LOC

• SAG COR LOC

• AX PD TSE FS

• AX GRE

• COR PD TSE

• SAG PD TSE

• COR MOD IR

• SAG T2 TSE FS

• SAG T2 TSE

• COR T2 TSE

Chen Lin PhD 3/2010

Outlines

• Conventional Spin Echo (CSE)

• Fast Spin Echo (FSE / TSE)

– 2D and 3D Fast Spin Echo (SPACE, CUBE)

× Single Shot Fast Spin echo (SSFSE, HASTE)

• Multi Contrast Spin Echo (T2 Mapping)

• Inversion Recovery (IR)

– FLAIR

– T1-FLAIR

– IR-FSE

– IR-SPGR / MP-RAGE

– Phase Sensitive ReconChen Lin PhD 3/2010

The Structure of MR Pulse SequencesMagnetization Preparation Section• Chemical Shift Selective Saturation / Excitation• Spatial Selective Saturation• Magnetization Transfer (MT), CHESS water suppression• Inversion Recovery (IR)

Data Acquisition Section• Slice/Slab Selective Excitation• Phase Encoding(s)• Signal Generation

• Spin Echo (SE), Fast SE (FSE/TSE), Single-shot FSE (SSFSE/HASTE)• Gradient Recalled Echo (GRE), Single-shot GRE (EPI)

• Diffusion Weighting (DWI/DTI) and Gradient Moment Nulling (GMN)• Frequency Encoding• Filling of K-space

Magnetization Recovery Section• Spoiling• Driven Equilibrium

Increment Phase

Encoding

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Conventional Spin Echo

Chen Lin PhD 3/2010

TE/2TE/2

Excitation Refocusing

Phase Encoding

Frequency Encoding

TRNext Excitation

rBW–Min. FOV–Chem. Shift–Distortion–SNR

Signal and Contrast of CSE

Max. signal when:

Excitation = 900

Refocusing = 1800

When TR>>TE:

Chen Lin PhD 3/2010

Short TR / Greater T1 Contrast

Long TE / Greater T2 contrast

PD

T1 ?

T2

Low SNR !

/ 1 / 2

0 (1 )TR T TE TS M e e

More Efficient Use of MR Signal

Chen Lin PhD 3/2010

t

900 x 1800 +y

SE

B1 / Mxy

FID

900 x 1800 +y

SEFID

TR = 400 – 4000 ms

TE = 10 – 200 ms

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Fast Spin Echo and CPMG Condition

Chen Lin PhD 3/2010

t

900 x

1800 +y 1800 -y 1800 +y

SE SE SE

B1 / Mxy

t 2t 2t

1. Refocusing RF pulses are 90 deg out of phase with respect to excitation RF pulse.

2. Identical spacing between refocusing RF pulses.

3. Identical phase accumulation between refocusing RF pulses.

Fast/Turbo Spin Echo Train

Chen Lin PhD 3/2010

Rewind

Echo Spacing

Echo Train Length (Turbo Factor)

Available TEeff in FSE/TSE

Echo Train Length = ? & Echo Spacing = ?Chen Lin PhD 3/2010

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RARE, FSE/TSE Sequence

t

Chen Lin PhD 3/2010

Short TEEffective Long TEEffective

B1 / Mxy

t 2t 2t

FSE/TSE Artifact

Chen Lin PhD 3/2010

CSE TE=30ms TSE ETL=30 EP=10ms TE=30ms

TSE ETL=30 EP=10msTE=130ms

ky

I

ky

I

ky

I

T2 Blurring and Edge Ringing

ky

kx

ky Y

II

Multi-shot FSE/TSE

I-space Point Spread Function

FT

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K-space Intensity Profile

Blurring

Ringing/Ghosting

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CSE FSE CSE FSE

FSE/TSE versus CSE

MT Effect

PD T2

Contrast

DifferenceBright FatChen Lin PhD 3/2010

T1 SE vs TSE of Hip Joint

Chen Lin PhD 3/2010

rBW = 485Hz/pix, ETL=5rBW = 485Hz/pix, ETL=1

Bright Fat with due to J-coupling

Lipid Mxy

TE(ms)

FSE/TSE with short echo spacing

CSE

CC

H

H

H

80 160

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CSE and TSE of Knee

SE, TE 14, 14cm, 3mm,

208 x 320, 3:04

TSE, Fat Sat, TE 14, 14cm,3mm,

208 x 320, 3:55

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Chen Lin PhD 3/2010

Driven Equilibrium (Fast Recovery, Restore)

• Add 180y + 90-x RF pulses to refocus and flip the Mxy

back to Z axis.

• Allow shorter TR ( ~2000ms) while maintaining T2w or PDw.

t

180y 90-x

X

Z

Y

Z

Y

90x

XChen Lin PhD 3/2010

Restore Example

TSE4 min

TSE with Restore2.4 min

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Stimulated Echo & CPMG

Mxy

t

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900 x

a10 y

SE SE + STE SE + STE

a20 y a30 y

Refocusing Flip Angle (RFA) < 1800

Contrast Difference between FSE and CSE

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RFA = 1500

RFA = 1800 RFA = 1200

CSE

Contrast Difference between FSE and CSE

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200

400

600

800

1000

1200

1400

1 2 3 4 5 6 7 8 9 101112131415161718

CSE

TSE_180

TSE_150

TSE_120

1300

1500

1700

1900

2100

2300

2500

2700

1 2 3 4 5 6 7 8 9 101112131415161718

CSE

TSE_180

TSE_150

TSE_120

TR/TE/ETL=2000/86/10TR/TE/ETL=2000/8.6/10

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3D FSE, SPACE, CUBESamplingPerfection withApplication optimizedContrast using different flip angleEvolutions

3D FSE/TSE w. variable refocusing flip angle schedules:

• Constant: same as 3D TSE

• PD Variant: optimized for short TE

• T2 Variant: optimized for longer TE

Constant Refocusing Flip Angles

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T2 Var. Refocusing Flip Angles

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Variations of 3D SPACE

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T1 SPACE1 x 1 x 3 mm³

FLAIR SPACE 1 x 1 x 1 mm³

T2 SPACE 1 x 1 x 1 mm³

Isotropic Hires T2 SPC of Brain

3D SPACE, GRAPPA 2, 0.9 x 0.9 x 0.9 mm3 4:27 min

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Chen Lin PhD 3/2010

3D FLAIR SPACE of Brain

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3D T2 SPACE of IAC

Acoustic Nerve

3D SPACE with 0.3 mm isotropic resolution in 6 min

3D T2 SPACE of Spine

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Reducing Susceptibility Artifact w. SPACE

2D TSE T2 MPR of 3D SPACE T2

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3D SPACE of Pelvis

Chen Lin PhD 3/2010

AX MPR of 3D Cor PD/T2 of Hip

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3D T1 FSE of Brain @ 3T

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3D T1 FSE of Pelvis @ 1.5T

Chen Lin PhD 3/2010

TR = 700ms TR = 553ms

3D SPACE Features

• Offers 3D imaging with isotropic resolution.

• Can be reformated to other planes or thicker 2D to improve SNR.

• Useful when multiple 2D of same contrast but different orientations are desired.

• Produces better image quality for PD and T2 than T1.

• Reduces SAR @ 3T.

• Helps minimize artifact from susceptibility.

Chen Lin PhD 3/2010

Multi Contrast Spin Echo

t

Mxy (TEn) = M0 exp(-TEn/T2)

Chen Lin PhD 3/2010

TE3TE2TE1

B1 / Mxy

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Cell

Water/

mobile

ions

GAG

+

-

++

++

+

+

+ +

+

+

+

+

+

++

-

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-

-

-

-

-

-

-

--

-

-

-

Morphology

Collagen

Biochemical Composure

Cartilage T2 Mapping

Chen Lin PhD 3/2010

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T2 Mapping of MCPJ for JRA

Chen Lin PhD 3/2010

11.5ms 23ms 34.5ms 46.0ms

57.5ms 69.0ms 80.5ms T2 MapT2 Map

RF

GS

ADC

GR

GP

180°

M0

Inversion Recovery

Tissue magnetization

Magnetization Preparation by IR

90° 180° 180° 180° 180° 180° 180°

Acquisition

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Variations of IR Technique

Inversion Options:

• Non-selective

• Slice-selective

• Spectral selective

• Adiabatic

• Flow-induced Adiabatic

• Combination of multiple inversions

Acquisition Options:

• Unlimited (TSE and TFL are common)

• 2D and 3D

• View ordering and correction of k-space modulation can be important.

Chen Lin PhD 3/2010

Applications of IR

• Selectively suppress tissue / background signal based on T1 differences– STIR, SPIR, SPAIR– FLAIR

• Improve T1 contrast (Phase Sensitive Recon)– MP-RAGE, IR-SPGR, IR-TFE– T1FLAIR– T1IR

• T1 Measurement / T1 Mapping• Tagging / Labeling

– Arterial Spin Labeling (ASL)

Chen Lin PhD 3/2010

T1 of Various Tissue Types

Tissue T1 @ 1.5T (msec)

T1 @ 3.0T (msec)

CSF 4400 4500

WM 780 850

GM 920 1330

Blood 1200 1500

Muscle 870 1160

Fat 220 260

TInull = 0.69 x T1

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STIR, FLAIR, TI and TINull

STIR: Short Tau Inversion Recovery, TRIM

FLAIR: FLuid Attenuated Inversion Recovery, “Dark Fluid”

TInull (Water)

Fat signal

Fluid signal

Inversion RF Pulse

Signal

TInull(Fat)

Time

Chen Lin PhD 3/2010

Interleave of Inversion & Acquisition

ACQ4

IR1

ACQ5

IR2

ACQ1

IR3

ACQ2

IR4

ACQ3

IR5

TI

ACQ1

IR1

TI

ACQ1

IR1

ACQ2

IR2

ACQ3

IR3

ACQ4

IR4

ACQ5

IR5

TI

IR2 IR3 IR4 IR5

ACQ2 ACQ3 ACQ4 ACQ5

STIR

FLAIR

T1IR

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FLAIR Optimization

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TI=2250ms TI=2500ms TI=2700ms

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From FLAIR to T1FLAIR

SignalLong TI and TRShort TI and TR

T1-weighted FLuid-Attenuated Inversion Recovery (T1FLAIR)

• Axial T1 FLAIR @ 3T with TR/TE/TI/ETL = 2100/9.5/900/3

• Improves T1 contrast at 3.0T

• High SAR limits number of slices and coverage

Chen Lin PhD 3/2010

T1 FLAIR of Spine

• Use shorter TR and TI than FLAIR (Modified FLAIR)• Suppress CSF and provides good T1 contrast

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Faster HR→ Shorter RR→ Less Recovery → Shorter TI

TI

TI

Adjust TI according to TR

Lock TI and TR for Tissue Suppression

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Double IR for Brain

Dark Fluid Dark Fluid & Dark WM

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Better Lesion Detection with DIR

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MP-RAGE, IR-SPGR

Either with Inversion Recovery or Saturation Recovery

Chen Lin, PhD 11/09

TI

Mz

IR

SPGR

MP-RAGE versus MP-EFGRE @ 3.0T

MP-RAGE 9:14 MP-EFGRE 6:30

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T1-weighted Imaging for Brain @ 3.0T

2D SE 60 2D T1 FLAIR 2D FLASH 3D FLASH 3D MPRAGE

IQ=4 IQ=6 IQ=4 IQ=5 IQ=5

IQ: The median perceived overall image quality

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Chen Lin PhD 3/2010

IR with Phase Sensitive (PS) Recon

Inversion

Signal

Time

Blood

Myocardium

True IR (Real IR) for Brain

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PS T1IR

PS T1IR T1SE T2 FLAIR

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Phase Sensitive Reconstruction

• An image reconstruction option, no additional scan time

• Improve contrast

• May produce artifact.

Ask for both magnitude recon and PS recon images.

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Look-Locker IR for T1 mapping

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Summary

• Main characteristics of spin echo pulse sequence.

• Variations of spin echo pulse sequence and their applications for Neuro and Ortho imaging.

• Key issues for optimizing spin echo based techniques.

Chen Lin PhD 3/2010

Thank You !

www.indiana.edu/~mri