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High Resolution Retinotopy with BOSS fMRI

High Resolution Retinotopy with BOSS fMRI. Peder Larson & Michael Lustig March 2005 Collaborator: Junjie Liu. Powered by. MR Imaging. Non-radiation Non toxic imaging modality. Flexible tissue contrast Arbitrary plane imaging Many applications. Outline. Retinotopy R40 MRI 101

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High Resolution Retinotopy with BOSS fMRI

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

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

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

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

  5. fMRI Retinotopy • 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. Boss fMRI 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.

  6. MRI101 - Nuclear Spins • Nuclear spin – intrinsic angular momentum • In imaging, mostly Hydrogennuclei • Random orientation Boss fMRI

  7. Spin Polarization Superconducting electromagnet • Spins polarize in a magnetic field, B0 • Net magnetization – M||B0 B0 M Boss fMRI * figure, courtesy of Bill Overall

  8. Spin Polarization Superconducting electromagnet * B0 M Boss fMRI * AVI’s, courtesy of Bill Overall

  9. Precession • Precession about z-axis. • Frequency B0 (Larmor) • f 64Mhz at 1.5T Boss fMRI * AVI’s, courtesy of Bill Overall

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

  11. RF Excitation – lab frame • RF field , B1 rotating at Larmor frequency, tips the magnetization. Boss fMRI * AVI’s, courtesy of Bill Overall

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

  13. Transverse Mxy e-t/T2 Time 1-e-t/T1 Longitudinal Mz Time Relaxation Boss fMRI * AVI’s, courtesy of Bill Overall

  14. fMRI101 – Cerebral Hemodynamics Hb - oxyhemoglobindHb - deoxyhemoglobin Rest dHb dHb Hb dHb dHb dHb Hb dHb Activation Hb Hb dHb dHb Hb Hb Hb dHb dHb Hb Hb Hb Hb dHb Hb Hb Hb dHb O2 consumption Blood Flow dHb Boss fMRI

  15. BOLD Contrast Boss fMRI

  16. BOLD Contrast Imaging Time-frame Boss fMRI

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

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

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

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

  23. Experimental Setup Junjie Miki Peder Boss fMRI

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

  25. Anatomical Image • SPGR, 0.75x0.75x2mm resolution • Centered in Visual Cortex, near V1 and V2 • Contrast between gray and white matter • Flow is bright Boss fMRI

  26. Functional Pulse Sequence • Balanced - Steady State Free Precession Sequence • Single slice 30 interleave spiral, w/ 10ms readout • TR/TE = 16.667/1.6 [ms] • Flip = 7degrees • Resolution = 1 [mm] inplane • Slice = 2mm (TBW=4) • Frame rate = 2 [frame/sec] Boss fMRI

  27. Raw Data Boss fMRI

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

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

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

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

  32. Comparison to BOLD Result BOLD(3T)* BOSS (1.5T)** Boss fMRI *Same order of SNR – ie. BOSS rocks! ** coverage gaps due to single slice

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

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

  35. 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. Boss fMRI

  36. 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 Boss fMRI

  37. References • Miller KL, Hargreaves BA, Lee J, Ress D, deCharms RC, Pauly JM Functional brain imaging using a blood oxygenation sensitive steady-state. Magnetic Resonance in Medicine 2003;50: 675-683 • Scheffler K, Seifritz E, Bilecen D, Venkatesan R, Hennig J, Deimling M, Haacke EM. Detection of BOLD changes by means of a frequencysensitive trueFISP technique: preliminary results. NMR Biomed 2001; 14:490 496. 27. • R. F. Dougherty, et al Visual field representations and locations of visual areas V1/2/3 in human visual cortex. Journal of Vision, 2003;3(10),586-598. • J. M. Santos, G.Wright, P. Yang and J. Pauly, Adaptive Architecture for Real-Time Imaging Systems, Proc. ISMRM 10th Scientific Meeting, 468, 2002 Boss fMRI

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

  39. The End Boss fMRI

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