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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