1. Bruce Fischl MGH ATHINOULA A. MARTINOS CENTER Harvard Medical School MIT CSAIL/HST some open issues in functional MRI (thanks to Larry Wald for almost all these slides)

2. Integrating Function and Structure. Local functional organization of cortex is largely 2- dimensional! From (Sereno et al, 1995, Science).

3. Some hot topics/open questions: 1.EPI distortions. 2.Large N arrays/parallel acquisition and High field (or ultra-high field). 3.Open issues.

4. EPI distortions: change with TE. 3T, TE = 21, 30, 40, 50, 60ms

5. EPI distortions: change with slice thickness.

6. EPI distortions: other factors 1.Scale linearly with field strength. 2.Change with changing shim. 3.Bone/air interface particularly problematic. 4.Are inversely proportional to bandwidth.

7. Some hot topics/open questions: 1.EPI distortions. 2.Large N arrays/parallel acquisition and High field (or ultra-high field). 3.Open issues.

8. Large N Arrays 1.The sensitivity of a coil generally scales inversely with its area. 2.The sensitivity of a coil falls off with depth, with the rate of falloff inversely proportional to the coil diameter. How to get uniformly high sensitivity? Tile the head with lots of little coils!

9. Two ways to improve sensitivity in the brain. Big magnet Small coils

10. Two ways to improve sensitivity in the brain. Big magnet Small coils

11. MGH array development 32 ch. at 3T 90 ch. at 1.5T 32 ch. at 7T

12. SNR Maps – increased sensitivity everywhere 23 Channel8 ChannelCP Head 0 10 20 30 40 50 90 Channel

13. Acceleration Arrays contain lots of redundant information (since each coil sees the entire brain, albeit with variable SNR) As usual in MRI, can tradeoff time and SNR – acceleration to increase EPI bandwidth and decrease distortion.

14. 1/FOV water kyky kxkx Under-sampled kspace Increasing Bandwidth: accelerate the EPI by leaving out every other line… 1/2 FOV, from under-sampled kspace

15. Two ways to get to the unfolded image… FFT kspace, every other line (under-sampled) Folded, but many FFT SMASH, GRAPPA SENSE

16. EPI distortions: acceleration 4x acceleration at 1.5T vs. no acceleration

17. 3D Flash with 16x accel. 1mm x 1mm x 2mm, acquisition time = 23sec Courtesy: Mathias Nittka, Siemens TR = 12 TE = 4.7 FA = 15 deg BW = 130 3T: 32 channel

18. What else can be done with SNR? Can also trade SNR for resolution, although the price is high!

19. MGH 3T 32 channel 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg

20. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 24

21. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 28

22. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 32

23. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 36

24. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 40

25. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 44

26. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 48

27. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 52

28. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 56

29. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 60

30. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel 64

31. 3T MP-RAGE 380um x 380um x 1mm, 7 scans of 9 minutes each motion corrected TI=900ms, TR/TE/flip = 2250/4.35/9deg MGH 3T 32 channel

33. Single shot GRE EPI 1.0mm isotropic, 192x192, TE= 30ms R=2 GRAPPA MGH 3T 32 channel

34. 1mm Res. Diffusion MRI iPAT=2iPAT=3 iPAT=5iPAT=4 Product EPI b = 1000 s/mm 2 256x256 matrix FoV = 256 mm Thick = 2.0 mm TR = 3200 ms TE (iPAT 2) = 112 ms TE (iPAT 3) = 94 ms TE (iPAT 4) = 87 ms TE (iPAT 5) = 87 ms Shots 12-30 Courtesy Michael Zwanger & Gunnar Kruger 3T 32 channel

35. Courtesy: G. Sorensen and R. Wang, Thomas Benner, MGH Martinos Center 2mm isotropic DTI, whole brain, 7 minutes

36. 7T array coil 750um isotropic resolution 7T High Resol. fMRI w/ BOSS method results from C. Miller, Univ. Oxford and C. Wiggins

37. 1.What to do about the veins? 2.How to accurately align high res functional data to structurals? 3.Non-Fourier reconstructions to account for other distortions? 4.What to do about physiological noise? 5.How to optimally combine different echoes? Open Questions for High-Field High resolution imaging.

38. 7 Tesla: Dielectric Resonance within head Intensity inhomogeneity in transmit B1 field (changes contrast!)

39. How to get rid of the veins? What is the true limit of the neural resolution of fMRI?

40. Larry Wald Graham Wiggins Andreas Potthast Chris Wiggins Franz Schmitt Christina Triantafyllou Gunnar Krueger Greg Sorensen Mattias Nitka Thomas Benner many others many others MGHSiemens Acknowledgements