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mcDESPOT Repeatability at 3T

mcDESPOT Repeatability at 3T. March 25, 2012 Jason Su. Questions. ASSET vs. ARC: How do parallel imaging artifacts propagate through to the maps? Is mcDESPOT w/ B-S B1 correction a repeatable experiment at 3T? What is the effect of inaccurate B1 on each of the maps?

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mcDESPOT Repeatability at 3T

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  1. mcDESPOT Repeatability at 3T March 25, 2012 Jason Su

  2. Questions • ASSET vs. ARC: How do parallel imaging artifacts propagate through to the maps? • Is mcDESPOT w/ B-S B1 correction a repeatable experiment at 3T? • What is the effect of inaccurate B1 on each of the maps? • How do the maps compare to 1.5T? • Does MWF remain the same? We would hope it would but does not for UBC group’s MWF

  3. Scanning • 1 volunteer • 2 scans, baseline and follow up exactly 24 hours later • Acceleration: 70% partial k-space, ASSET 2 or ARC 2x1.5 • B-S: TR 500ms, BS FA 270 deg., 32x32 22cm FOV, 6mm slice • Day 0 – no HOS • 8ch head coil: ASSET, ARC • 32ch head coil: ASSET • Day 1 – some HOS • 8ch head coil: ASSET (SSFP HOS), ARC (HOS) • 32ch head coil: ASSET (no HOS), ARC (no HOS) • 6:30 for one complete mcDESPOT protocol at 2mm isotropic

  4. Post-Processing • B-S B1 maps via updated Orchestra recon • Converted to flip angle then “kappa” maps • xmtAddScan and xmtAddFTG are stored in header for efgre3d22M4v04 • Need to add ia_rf1 to header, assuming now that = 32767 when xmtAddScan < 200, otherwise unknown (thankfully not the case) • Linear interpolation from 27 to 80 slices • 3T2 protocol expiry? Interest in getting it running at Sherman and 3T3. • Registration to intermediate “halfway” space • Distributes interpolation errors/blur equally between two volumes • Allows for much better voxelwisecomparison • White matter segmentation is performed with FSL FAST on the registration target • The mask is then eroded with a spherical kernal of radius 2mm to stay away from possible GM edges

  5. ASSET vs. ARC • Images and maps are presented without B1 correction • Would have added an additional variable and not needed for this comparison • Artifacts are more prominent in ASSET • Clear skull aliasing artifact running through center of images • How do parallel imaging artifacts propagate through to the maps?

  6. Sample Images: 32ch ASSET SPGR

  7. Sample Images: 32ch ARC SPGR

  8. Sample Images: 8ch ASSET SPGR

  9. Sample Images: 8ch ARC SPGR

  10. 32ch ASSET: Single T1

  11. 32ch ARC: Single T1

  12. 32ch: Single T1

  13. 32ch: Single T1 in WM

  14. 8ch: Single T1

  15. 8ch: Single T1 in WM

  16. 32ch ASSET: Single T2

  17. 32ch ARC: Single T2

  18. 32ch: Single T2

  19. 32ch: Single T2 in WM

  20. 8ch: Single T2

  21. 8ch: Single T2 in WM

  22. 32ch ASSET: MWF

  23. 32ch ARC: MWF

  24. 32ch: MWF

  25. 32ch: MWF in WM

  26. 8ch: MWF

  27. 8ch: MWF in WM

  28. Conclusions • 32ch coil seems to give less consistent results than 8ch for ARC vs. ASSET • Artifacts are more apparent with 32ch (surprising?) and are responsible for higher percent difference than 8ch • 8ch SPGR images appear better with ASSET • MWF seems less affected by the artifacts than T1 and T2, or at least harder to see

  29. Repeatability • Is mcDESPOT w/ B-S B1 correction a repeatable experiment at 3T? • Will show 8ch ASSET, 8ch ARC, 32ch ASSET • 32ch ARC was not collected at baseline

  30. Sample Image: Kappa Map

  31. Sample Image: Kappa Map

  32. 8ch ASSET 0d: Single T1

  33. 8ch ASSET 1d: Single T1

  34. 8ch ASSET: Single T1

  35. 8ch ASSET: Single T1 in WM

  36. 8ch ARC: Single T1

  37. 8ch ARC: Single T1 in WM

  38. 32ch ASSET: Single T1

  39. 32ch ASSET: Single T1 in WM

  40. 8ch ASSET 0d: Single T1

  41. 8ch ASSET 1d: Single T2

  42. 8ch ASSET: Single T2

  43. 8ch ASSET: Single T2 in WM

  44. 8ch ARC: Single T2

  45. 8ch ARC: Single T2 in WM

  46. 32ch ASSET: Single T2

  47. 32ch ASSET: Single T2 in WM

  48. 8ch ASSET 0d: MWF

  49. 8ch ASSET 1d: MWF

  50. 8ch ASSET: MWF

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