1. MR RL High Resolution Retinotopy with BOSS fMRI Peder Larson & Michael Lustig March 2005 Collaborator: Junjie Liu Powered by

2. MR RL Boss fMRI 2 MR Imaging Non-radiation Non toxic imaging modality. Flexible tissue contrast Arbitrary plane imaging Many applications

3. MR RL Boss fMRI 3 Outline Retinotopy R40 MRI 101 –Basic MR physics fMRI 101 –Functional MRI basics – BOLD fMRI 201 –BOSS fMRI Results

4. MR RL Boss fMRI 4 Retinotopy R40 Mapping the retina to cortex One-to-one mapping from retinal stimulation to primary visual cortex (V1) –First step in visual processing V1 Images from “The Primary Visual Cortex”, Matthew Schmolesky, http://webvision.med.utah.edu/VisualCortex.htmlhttp://webvision.med.utah.edu/VisualCortex.html

5. MR RL Boss fMRI 5 fMRI Retintopy Expanding rings and rotating wedges used as stimuli for radial and angular mapping Source: R. F. Dougherty, et al (2003). Visual field representations and locations of visual areas V1/2/3 in human visual cortex. Journal of Vision, 3(10),586-598. Source: HTML: Visual field representations and locations of visual areas V1/2/3 in human visual cortex (Download PDF) R. F. Dougherty, V. M. Koch, A. A. Brewer, B. Fischer, J. Modersitzki and B. A. Wandell (2003). Visual field representations and locations of visual areas V1/2/3 in human visual cortex. Journal of Vision, 3(10),586-598, DOI 10.1167/3.10.1.HTML: Visual field representations and locations of visual areas V1/2/3 in human visual cortex (Download PDF)

6. MR RL Boss fMRI 6 MRI101 - Nuclear Spins Nuclear spin – intrinsic angular momentum In imaging, mostly Hydrogen nuclei Random orientation

7. MR RL Boss fMRI 7 Spin Polarization Spins polarize in a magnetic field, B 0 Net magnetization – M||B 0 B0B0 M Superconducting electromagnet * figure, courtesy of Bill Overall

8. MR RL Boss fMRI 8 Spin Polarization B0B0 M Superconducting electromagnet * * AVI’s, courtesy of Bill Overall

9. MR RL Boss fMRI 9 Precession Precession about z-axis. Frequency   B 0 (Larmor) f  64Mhz at 1.5T * AVI’s, courtesy of Bill Overall

10. MR RL Boss fMRI 10 MR Signal Only Transverse Magnetization induces current which is picked by an RF coil

11. MR RL Boss fMRI 11 RF Excitation – lab frame RF field, B 1 rotating at Larmor frequency, tips the magnetization. * AVI’s, courtesy of Bill Overall

12. MR RL Boss fMRI 12 RF Excitation - rotating frame Simplification: Coordinates rotate at Larmor frequency Excitation becomes rotation RF 90° Pulse-sequence diagram * AVI’s, courtesy of Bill Overall

13. MR RL Boss fMRI 13 Relaxation Time Transverse M xy e -t/T2 Time 1-e -t/T1 Longitudinal M z * AVI’s, courtesy of Bill Overall

14. MR RL Boss fMRI 14 fMRI101 – Cerebral Hemodynamics Hb - oxyhemoglobindHb - deoxyhemoglobin dHb Hb dHb Hb Rest Activation O 2 consumption Blood Flow dHb

15. MR RL Boss fMRI 15 BOLD Contrast

16. MR RL Boss fMRI 16 BOLD Contrast Imaging Time-frame

17. MR RL Boss fMRI 17 BOLD issues Blood Oxygenation Level Dependent Poor SNR Poor spatial/temporal resolution Image artifacts Signal loss sinuses

18. MR RL Boss fMRI 18 fMRI201 - Steady State imaging Fast High SNR efficiency Less artifact problems Frequency sensitive RF … °°  ° °° * AVI’s, courtesy of Bill Overall

19. MR RL Boss fMRI 19 BOSS fMRI Blood Oxygenation Sensitive Steady State dHb Hb * figure, courtesy of Dr. Karla Miller

20. MR RL Boss fMRI 20 BOSS fMRI Deoxy signal subtracts from Oxy signal dHb Hb rest activation dHb Hb

21. MR RL Boss fMRI 21 BOSS fMRI Advantages: –Fast –SNR efficient –High functional sensitivity –No artifacts Caveat: –Functional sensitivity to a small region of the brain Uses: –High resolution fMRI

22. MR RL Boss fMRI 22 Our Retinotopy Three Stimuli: –Expanding ring –Rotating Wedge –Full Field On/Off 161 second experiments 24 second period Repeated each experiment twice

23. MR RL Boss fMRI 23 Experimental Setup Miki Peder Junjie

24. MR RL Boss fMRI 24 Protocol 1.Subject placed into magnet 2.Acquire anatomical reference image 3.Run various visual stimuli and acquire functional data 4.Repeat (3) for improved signal-to-noise ratio

25. MR RL Boss fMRI 25 Anatomical Image SPGR, 2x1x1mm resolution Centered in Visual Cortex, near V1 and V2 Contrast between gray and white matter Flow is bright

26. MR RL Boss fMRI 26 Raw Data

27. MR RL Boss fMRI 27 Full Field Stimulus Correlation used to determine activation Activation only on gray matter throughout slice Average of 2 scans

28. MR RL Boss fMRI 28 Expanding Ring Time-varying activation as ring expands Red = activated by inner rings Blue = activated by outer rings

29. MR RL Boss fMRI 29 Expanding Ring – 3D Data mapped onto 3D anatomical image Gaps in coverage because only one slice was imaged

30. MR RL Boss fMRI 30 Expanding Ring – 2D projection Reformat of 3D image to 2D plane Again, coverage gaps due to single slice Activation begins in upper left

31. MR RL Boss fMRI 31 Comparison to BOLD Result Result from previous multislice study on same volunteer Correlates well with BOSS result –Primary differences in upper left (foveal area) BOSS BOLD

32. MR RL Boss fMRI 32 Full Field Coherence Result Shows similar activation to correlation No timing information High coherence only in gray matter, not white matter

33. MR RL Boss fMRI 33 Full Field Amplitude Result Thresholded to show only >0.3 coherence Primarily ~4% amplitude activation Extremely high amplitude (~25%) near vessels (%)

34. MR RL Boss fMRI 34 Conclusions BOSS fMRI works for retinotopy! SNR is promising and comparable to BOLD in 3T. Faster imaging enables 3D volume acquisitions with better spatial/temporal resolution.

35. MR RL Boss fMRI 35 Future BOSS Projects Potential for very high resolution (< 1 mm) studies 3D scan for larger volumetric coverage Ocular Dominance –Requires < 1mm resolution –Switch between using left and right eye Better Retinotopy –3D and various center frequencies for more coverage

36. MR RL Boss fMRI 36 Thank Yous Junjie Liu – Retinotopy help, data analysis help, and ideal subject Jongho Lee – BOSS expert Juan Santos – Real-time MRI Jedi master

37. MR RL Boss fMRI 37 The End