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High Resolution 3D Diffusion Pulse Sequence

High Resolution 3D Diffusion Pulse Sequence. Dept. of Radiology Medical Imaging Research Lab. University of Utah. Eun-Kee Jeong, Ph.D. Seong-Eun Kim, Ph.D. Gregory Katzman, M.D. Dennis L. Parker, Ph.D. Diffusion MRI BASICS. Signal loss : by intra-voxel phase dispersion.

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High Resolution 3D Diffusion Pulse Sequence

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  1. High Resolution 3D Diffusion Pulse Sequence Dept. of Radiology Medical Imaging Research Lab. University of Utah Eun-Kee Jeong, Ph.D. Seong-Eun Kim, Ph.D. Gregory Katzman, M.D. Dennis L. Parker, Ph.D.

  2. Diffusion MRI BASICS

  3. Signal loss : by intra-voxel phase dispersion At the echo time TE, NMR signal is decayed by, - T2 decay (spin-spin diffusion) - diffusive motion For any set of diff. gradient pulses G G 90 180 echo TE

  4. Diffusion Imaging : Detection of Acute Stroke Conventional T2 WI DW-EPI

  5. CELL EXTRA-CELLULAR SPACE FREELY DIFFUSING WATER IN EXTRA-CELLULAR SPACE Diffusion Imaging: Principles • Diffusion gradients sensitize MR Image to motion of extra-cellular water • Higher diffusive motion  lower signal intensity Tissue Sample A Tissue Sample B Freely Diffusing Water = Dark Larger D Restricted Diffusion = Bright Smaller D

  6. PE FE SS Diff. Grad. along different axis X Diffusion-Weighting Y Diffusion-Weighting Z Diffusion-Weighting GFE GPE GSS RF

  7. Diffusion Imaging : TRACTOGRAPHY arc. fasciculus unc. fasciculus

  8. Diffusion EPI: GOOD & BAD • . DWIprobes micro motion of H2O in tissue. • . Largest diffusion in body (CSF): • drift velocity vd = ~0.1mm/sec(ADC = ~2.6x10-3 mm2/sec) • Dx = ~10mm/100ms TE  Requires large gradient!! • . Any physiological motion • - velocity v > ~10 mm/sec -> too huge for diff. gradient • - motion induced artifact on Multi-shot DWI • One-shot EPI-DWI freezes physiological motion. • . Susceptibility artifact

  9. Single-/Multi-shot EPI-DWI PE single-shot DW-EPI 8 shots DW-EPI CSF motion artifact Off-line correction needed!

  10. Geometric Distortion in DW-EPI  non-EPI DW MRI. DW Propeller (2D FSE based + Motion correection) DW EPI b=0 b=1000 b=0 b=1000 A patient with post-op symptoms, aneurysm clip caused artifacts in EPI.

  11. To develop a high-res., non-EPI Diff., and multi-shot pulse sequence. PURPOSE

  12. 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 Preparation 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. METHODS

  13. 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 a 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 p/2+x p+y p-yp/2-x 3D Seg.SSFP RF GD METHODS

  14. a a a a a a a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -a a RF GFE GPE GSE TR Segmented 3D SSFP a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a 3D Seg. SSFP 3D SSFP: maintain high steady state (longitudinal & transverse) Diff. Prep.

  15. 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. Acquired signal Diff. Prep. Magnetization + Re-grown Magnetization

  16. Dt b b b TR Longitudinal Magnetization for ntha pulse Typical imaging parameters Mss: Longitudinal steady-state magnetization N : Number of echoes : 32, 48, 64 Dt : effective echo spacing : ~ 4 ms T1: spin-lattice relaxation time : ~ 800 ms a : flip angle : 15 ~ 45o To be minimized!!

  17. CENTRIC View-Ordering: 3D Seg.SSFP-DW centric non-centric b = 500 Significant re-grown magnetization Mostly DW magnetization slice encoding Grad. echo number  echo number 

  18. RESULTS

  19. 3ddw: SRSS: dog heart vs. EPI DW (fresh in ethanol 70% + water 30 %) b = 0 b = 500 EPI(256x128) 3D SSSFP 256x192x48etl:48 TE:66ms FOV: 16cm/2.5 mm tone_factor = 0.4 rf10_on = 0 opflip = 45o SpSat: Default S/I

  20. 3D Seg.SSFP-DW: Human Volunteer b: 0 (S/I) 250 750 ADC map optic nerve 256x256x64etl:32 0.86x0.86x1.5 mm3 RCVR BW: 62.5kHz NEX: 2 a = 48o

  21. CONCLUSION • Segmentation of 3D SSFP: successful • Chemical fat saturation • Spatial saturation • Diffusion gradients • 3D Segmented SSFP-DW • High Resolution 3D DWI is acquired. • Almost No susceptibility artifact • Anisotropy is observed. Problem: table vibration  ????

  22. G G 4 (a) (b) G 1 23 t t Gradient t=0 t1 t1+t t2 t2+t x1 x2(=0) x3 90 180 x RF z z z z + + 3 4 1 4 y 1 1 2 2 2 2 3 3 4 3 1 x x x x t1 t1+t t2 t2+t Phase: stationary & moving spins

  23. GFE GPE GSE RF ChemSat Diff.Prep SpSat a’-a/2 - a -Echo Train… … - a -a/2 3D Seg.SSFP-DWSptial SAT, Chem Sat, DW Prep ON Diffusion Prep.

  24. b = 0 200400 700 3D Seg.SSFP-DW: ph-/sl-encoding order? Excised dog heart preserved in formalin  T1 : ~200 ms 256x160x32, FOV = 16cm, Dz = 1.5mm Diffusion grad. along R/L.

  25. Apodization w/ zero-Filling: 512 ZIP2, ZIP512 No apodization gaussian apodization Trianglular Apod.  SS 256x256x64:phFOV 0.75etl:48 FOV: 25.6cm/1.0 mm(isotropic) tone_factor = 0.4 rf10_on = 0 opflip = 45o SpSat: OFF encode_mode=1 (Y-centric), TR/TE: ~250/~60 ms Scan time: ~1:00 min. 512x256x96(True ACQ.) 256x256

  26. 3D Seg.SSFP-DW: along different direction A/P R/L S/I 256x256x64 etl:32 0.86x0.86x1.5 mm3 RCVR BW: 62.5kHz a = 48o NEX: 1

  27. 0 100 200 400 3ddw: dog heart (1 yr old) 07-19-02 D = 0.5x10- 3mm2/sec

  28. Signal Intensity vs. b value Single exponential decay Signal from re-grown Mag.: negligible b = 0 (S/I) D = 1.48x10-3 mm2/sec ADC Map

  29. 3D Seg.SSFP-DW:Fresh Celery b = 0 b = 750 A/P R/L S/I 256x160x64 etl:64 NEX: 2 FOV: 16 cm Sl. thickness: 3.0mm a = 40o ADC maps

  30. p/2+x p+y p-yp/2-x 3D Seg.SSFP RF GD 3D Seg.SSFP-DW: SpSat, DTIPrep p/2 - p - p - p/2 1/ON, 0/OFF centric non-centric • 256x192x32 • = 45o TR:min • FOV = 16cm • sl.thick.=2.0mm • b = 500  S/I 1-1-1-1 1-1-1-0 1-1-1-0

  31. 3ddw: SRSS (Square root of Sum of squares) S/I R/L A/P R/L+A/P A/P+S/I S/I+R/L 07-19-02 256x192x48etl:48 TE:66ms FOV: 16cm/1.5 mm SpSat: Default S/I tone_factor = 0.4 Head coil opflip = 45o rf10_on = 0 tipup_f=0

  32. 3D Seg.SSFP-DW vs. EPI-DW 3D SSSFP EPI(256x128) b=750 b=750 S/I A/P

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