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fMRI: Biological Basis and Experiment Design Lecture 6: Pulse Sequences, Hardware, Software

This lecture covers the hardware and software components of fMRI experiments, including coils, amplifiers, electromagnetic radiation, and pulse sequence diagrams.

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fMRI: Biological Basis and Experiment Design Lecture 6: Pulse Sequences, Hardware, Software

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  1. fMRI: Biological Basis and Experiment DesignLecture 6: Pulse Sequences • Hardware • Software www.hoghaven.com

  2. Hardware • Coils • RF • Gradient RF Head coil from www.nmr.mgh.harvard.edu/~rhoge/HST583/doc/HeadCoil.jpg Gradient coil picture from www.med.umn.edu/.../cvs/martin/gallery.html • Amplifiers • RF • Input • Output ("pre-amp") • Gradient

  3. RF Hardware for NMR experiments

  4. Electromagnetic radiation • Electromagnetic energy (light, RF wave, radiated heat) travels as a pair of oscillating electric and magnetic fields • Polarization is determined by the orientation of the E field ls7pm3.gsfc.nasa.gov/whatsRM/em.html

  5. Parallel Imaging Arrays at 7T 2002 2003 Start: 4 Loop 8 Loop 8 Strip 16 Strip 15 Strip Open 32 Strip 2004

  6. Software SYNGO console - choose pulse sequence - set parameters - ... - image display and storage MR-IR - image reconstruction Can't remember name - final safety checks - send actual commands to hardware

  7. Parts of a pulse sequence • Magnetization preparation: when equilibrium doesn't give you the contrast you want • Important timing parameter: TI = inversion time • Excitation: rotate (prepared) magnetization to transverse plane • Important timing parameter: TR = repetition time • Read-out: detect transverse magnetization • Important timing parameter: TE = echo time

  8. Pulse sequence diagrams Magnetization preparation Excitation Read-out Nrep RF GSS GPE GRO DAC

  9. Magnetization preparation T1-contrast enhanced by inversion preparation No inversion preparation

  10. Inversion recovery (magnetization preparation) An image taken at this point will have white matter brighter than gray matter; no signal from CSF

  11. Inversion recovery (partial volume effects) An image taken at this point will have a black boundary between white / gray and CSF (which won't be black)

  12. T1-contrast in repeated measurements

  13. Pulse sequence diagram: MP-RAGE (256 x 256) Inversion pulse Nrep = 256 Inversion time Excitation pulse TR ~ 10 ms RF GSS PE table increments each repetition GPE GRO 256 points DAC

  14. Read-out: echo time and total duration

  15. Pulse sequence diagram: EPI (128 x 128 image) Inversion pulse TR =2500 ms Nrep = 64 TI = 900ms RF GSS GPE GRO 128 pts 128 pts DAC

  16. Acquired data: k-space

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