High Resolution 3D Diffusion Pulse Sequence

Dept. of RadiologyMedical Imaging Research Lab.

University of Utah

Eun-Kee Jeong, Ph.D.Seong-Eun Kim, Ph.D.Ph.D.Gregory Katzman, M.D.M.D.Dennis L. Parker, Ph.D.

Diffusion MRIDiffusion MRIBASICSBASICS

G

18090

G

echoTE

At the echo time TE, NMR signal is decayed by, - T2 decay (spin-spin diffusion) - diffusive motion

ijij2DbTTE

oij eeSbTES /),(

b D G D Gij ij i ij j ( / )

b G2 ( / )

For any set of diff. gradient pulses

Signal loss Signal loss : : by intra-voxel phase dispersionby intra-voxel phase dispersion

Conventional TConventional T22 WI WI DW-EPIDW-EPI

Diffusion Imaging : Diffusion Imaging : Detection of Acute StrokeDetection of Acute Stroke

Diffusion gradients sensitize MR Image to motion of extra-cellular water

Higher diffusive motion lower signal intensity

Tissue Sample ATissue Sample A Tissue Sample BTissue Sample B

Freely Diffusing Water = DarkFreely Diffusing Water = Dark Larger DLarger D

Restricted Diffusion = BrightRestricted Diffusion = Bright Smaller DSmaller D

Diffusion Imaging: PrinciplesDiffusion Imaging: Principles

CELLCELL

EXTRA-CELLULAR SPACEEXTRA-CELLULAR SPACE

FREELY DIFFUSING WATER INFREELY DIFFUSING WATER INEXTRA-CELLULAR SPACEEXTRA-CELLULAR SPACE

X Diffusion-WeightingX Diffusion-Weighting Y Diffusion-WeightingY Diffusion-Weighting Z Diffusion-WeightingZ Diffusion-Weighting

GGFEFE

GGPEPE

GGSSSS

RFRF

Diff. Grad. along different axisDiff. Grad. along different axis

SS

PE

FE

Diffusion Imaging : Diffusion Imaging : TRACTOGRAPHYarc. fasciculus

unc. fasciculus

. DWI. DWI probes micro motion of Hprobes micro motion of H22O in tissue.O in tissue.

. Largest diffusion in body (CSF): . Largest diffusion in body (CSF): -drift velocity drift velocity vvd d = ~0.1mm/sec= ~0.1mm/sec (ADC = ~2.6x10(ADC = ~2.6x10-3 -3 mmmm22/sec)/sec)

x = ~10x = ~10m/100ms TE m/100ms TE Requires large gradient!! Requires large gradient!!

. Any physiological motion. Any physiological motion- velocity - velocity v v > ~10 mm/sec> ~10 mm/sec -> too huge for diff. gradient -> too huge for diff. gradient- - motion induced artifactmotion induced artifact on on Multi-shotMulti-shot DWI DWI

-One-shot EPI-DWI freezes physiological motionOne-shot EPI-DWI freezes physiological motion..

. Susceptibility artifact. Susceptibility artifact

Diffusion EPI: GOOD & BADDiffusion EPI: GOOD & BAD

single-shot DW-EPIsingle-shot DW-EPI 8 shots DW-EPI8 shots DW-EPICSF motion artifactCSF motion artifactOff-line correctionOff-line correction needed! needed!

PP EE

Single-/Multi-shot EPI-DWISingle-/Multi-shot EPI-DWI

Geometric Distortion in DW-EPIGeometric Distortion in DW-EPI non-EPI DW non-EPI DW MRI.MRI.

DW EPIDW Propeller

(2D FSE based + Motion correection)

A patient with post-op symptoms, aneurysm clip caused artifacts in EPI.

b=0 b=0b=1000 b=1000

PURPOSETo develop a high-res., non-EPI Diff., and multi-shot pulse sequence.

METHODS

• Multi-shot, 3D pulse sequence for higher SNR.- Multi-shot Motion-induced phase must be corrected.

• Motion correction or motion insensitive pulse sequence- Navigator echo technique is not used.- Diffusion PreparationPreparation technique Used!- Small motion may not degrade the resultant images.

• High resolution: Imaging matrix 256 read-out- EPI: 128 Read-out 256 RO will generate more geometric

distortion.

METHODSMETHODS Started from GE’s 3D SSFP (FIESTA)

• Segmentation of 3D SSFP- Gradient balancing is interrupted. some loss of steady state.- Multi-shot 3DFSE-like (CPMG) pulse sequence.- Each RF pulse tips some longitudinal magnetization to

transverse plane.

• Segmented 3D SSFP-DW - Diffusion is encoded as Prep. Pulses in between two

segmentations.- Any phase error caused during DW Prep will be lost by 90-x amplitude modulated

3D Seg.SSFP3D Seg.SSFP

+x +y-y-xRF

GD

3D Seg. SSFP

Segmented 3D SSFPTRTR

RF

GFE

GPE

GSE

3D SSFP: maintain high steady state (longitudinal & transverse)

Diff. Prep.

Acquired signal Acquired signal Diff. Prep. Magnetization Diff. Prep. Magnetization + Re-grown Magnetization + Re-grown Magnetization MR signal is mixture of:

- Diffusion prepared magnetization- Re-grown magnetization

- Will be significant for spins with short T1.

: T1 (brain tissues) = ~800 ms long enough!

- More for non-centric ordering of phase-/slice-encoding

- Centric slice ordering was used to reduce the contribution of re-grown spins.

Longitudinal Magnetization for nLongitudinal Magnetization for nthth pulsepulse

Typical imaging parametersTypical imaging parametersMss: Longitudinal steady-state magnetization

N : Number of echoes : 32, 48, 64t : effective echo spacing : ~ 4 msT1: spin-lattice relaxation time : ~ 800 ms

: flip angle : 15 ~ 45o

b

t

b bTR

1

1

1

/

/)1()1(

1

/

cos1

cos1cos Tt

Ttnn

oTtnnbD

SSnz e

e

T

tMeeMM

To be minimized!!

CENTRIC View-Ordering: CENTRIC View-Ordering: 3D Seg.SSFP-DW3D Seg.SSFP-DW

Significant re-grown magnetizationMostly DW magnetization

echo number echo number

slic

e en

codi

ng G

rad.

centric non-centric

b = 500b = 500

RESULTS

3ddw: SRSS: 3ddw: SRSS: dog heart vs. EPI DWdog heart vs. EPI DW (fresh in ethanol 70% + water 30 %)(fresh in ethanol 70% + water 30 %)

256x192x48 etl:48 TE:66msFOV: 16cm/2.5 mmtone_factor = 0.4 rf10_on = 0 opflip = 45o SpSat: Default S/I

EPI(256x128) EPI(256x128)

3D SSSFP3D SSSFP

b = 0b = 0 b = 500b = 500

3D Seg.SSFP-DW: 3D Seg.SSFP-DW: Human VolunteerHuman Volunteer b: 0 (S/I) 250 750 b: 0 (S/I) 250 750 ADC mapADC map

256x256x64 etl:32 0.86x0.86x1.5 mm3

RCVR BW: 62.5kHz NEX: 2 = 48o

optic nerveoptic nerve

CONCLUSION• Segmentation of 3D SSFP: successfulSegmentation of 3D SSFP: successful

- Chemical fat saturationChemical fat saturation- Spatial saturationSpatial saturation- Diffusion gradientsDiffusion gradients

• 3D Segmented SSFP-DW3D Segmented SSFP-DW- High Resolution 3D DWI is acquired.High Resolution 3D DWI is acquired.- Almost No susceptibility artifactAlmost No susceptibility artifact- Anisotropy is observed.Anisotropy is observed.

Problem: table vibration ????

G

18090

G

(a) (b)

t=0 tt=0 t1 1 t t11++ t t2 2 t t22++

Gradient

RF

Phase: stationary & moving spinsPhase: stationary & moving spins

1122

33

x

z

11

22

33

++

x

z

44

11

22

33

x

z

44

y 1122

33

++

x

z

tt1 1 t t11++ t t2 2 t t22++

44

1 2 3

xx

4

xx1 1 x x22(=0)(=0) x x33

G

3D Seg.SSFP-DW Sptial SAT, Chem Sat, DW Prep ON

ChemSat Diff.Prep SpSat ’- Echo Train … … - -

GGFEFE

GGPEPE

GGSESE

RFRF

Diffusion Prep.Diffusion Prep.

3D Seg.SSFP-DW: ph-/sl-encoding order?

256x160x32, FOV = 16cm, 256x160x32, FOV = 16cm, z = 1.5mm z = 1.5mm

Diffusion grad. along R/L. Diffusion grad. along R/L.

b = 0 200 400 700

Excised dog heartExcised dog heart preserved in formalin preserved in formalin T T11 : ~200 ms : ~200 ms

Apodization w/ zero-Filling: Apodization w/ zero-Filling: 512 ZIP2, ZIP512512 ZIP2, ZIP512

256x256256x256

No apodizationNo apodization gaussian apodizationgaussian apodization Trianglular Apod. Trianglular Apod. SS SS

512x256x96(True ACQ.)

256x256x256x256x64:phFOV 0.7564:phFOV 0.75 etl:48etl:48

FOV: 25.6cm/1.0 mm(isotropic)FOV: 25.6cm/1.0 mm(isotropic)

tone_factor = 0.4 rf10_on = 0 tone_factor = 0.4 rf10_on = 0

opflip = 45opflip = 45o o SpSat: OFF SpSat: OFF

encode_mode=1 (Y-centric), encode_mode=1 (Y-centric),

TR/TE: ~250/~60 msTR/TE: ~250/~60 ms

Scan time: ~1:00 min.Scan time: ~1:00 min.

3D Seg.SSFP-DW3D Seg.SSFP-DW: : along different directionalong different direction

A/P R/L S/IA/P R/L S/I

256x256x64

etl:32

0.86x0.86x1.5 mm3

RCVR BW: 62.5kHz

= 48o

NEX: 1

3ddw: 3ddw: dog heart (1 yr old)dog heart (1 yr old) 07-19-0207-19-02

D = 0.5x10- 3mm2/sec

0 1000 100

200 400200 400

Signal Intensity vs. b valueSignal Intensity vs. b value

b = 0 (S/I)b = 0 (S/I)

SI vs. b

b (sec/mm2)

SI

0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0

D = 1.48x10D = 1.48x10-3-3 mm mm22/sec/secADC MapADC Map

Single exponential decaySingle exponential decay

Signal from re-grown Mag.: negligibleSignal from re-grown Mag.: negligible

3D Seg.SSFP-DW3D Seg.SSFP-DW:: Fresh CeleryFresh Celeryb = 0 b = 750 b = 0 b = 750

A/P R/L S/IA/P R/L S/I

256x160x64

etl:64

NEX: 2

FOV: 16 cm

Sl. thickness: 3.0mm

= 40o

ADC mapsADC maps

3D Seg.SSFP-DW3D Seg.SSFP-DW: : SpSat, DTIPrepSpSat, DTIPrep

256x192x32256x192x32= 45o

TR:minTR:min

FOV = 16cmFOV = 16cm

sl.thick.=2.0mmsl.thick.=2.0mm

b = 500 b = 500 S/I S/I

1/ON, 0/OFF1/ON, 0/OFF

1-1-1-1 1-1-1-0 1-1-1-0

3D Seg.SSFP3D Seg.SSFP

+x +y-y-x

RF

GD

non-centricnon-centric centriccentric

3ddw: 3ddw: SRSS (SRSS (Square root of Sum of squaresSquare root of Sum of squares))

07-19-0207-19-02 S/I R/L A/PS/I R/L A/P

R/L+A/P A/P+S/I S/I+R/L R/L+A/P A/P+S/I S/I+R/L

256x192x48 etl:48 TE:66ms FOV: 16cm/1.5 mm SpSat: Default S/Itone_factor = 0.4 Head coil opflip = 45o rf10_on = 0 tipup_f=0

3D Seg.SSFP-DW vs. EPI-DW3D Seg.SSFP-DW vs. EPI-DW3D SSSFP EPI(256x128) 3D SSSFP EPI(256x128)

b=750 b=750 b=750 b=750

S/I

A/P

S/I

A/P