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Stimulus Presentation and Image Acquisition

Stimulus Presentation and Image Acquisition. Valentina Petre. How do we Design an Experiment. Block design. Event related. Block design. * Very good statistical power * Good for “all or none” phenomena (example visual, or acoustic stim)

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Stimulus Presentation and Image Acquisition

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  1. Stimulus Presentation and Image Acquisition Valentina Petre

  2. How do we Design an Experiment Block design Event related

  3. Block design * Very good statistical power * Good for “all or none” phenomena (example visual, or acoustic stim) * Good for an initial experimental probe – pilot study (exceptions) * The optimal block length 14 to 20 s * Do not depend much on the assumption of a certain hemodynamic function * Subject might anticipate the stimulus

  4. Event related * Multiple trials presentation in one run * Optimum time 16s * Close trials 4s –still can be separated * You must assume linearity * Depend on the model of the hemodynamic function * Reduced in sensitivity – vary the inter trial interval

  5. Event Related stimulus presentation desynchronized from scanner acquisition Slice i Stim on Frame aq

  6. Protocols available Protocol Prop Interleaved Ascending

  7. Small voxel volume, low signal Large voxel, high signal Air tissue interface Tissue Air The field inhomogeneity is large, thus it will cause large phase dispersion across the voxel. The signal is reduced.

  8. How to avoid intravoxel dephasing • Reduce the slice thickness. The longest dimension of your voxel should not be parallel with the direction of field variation • Orient the slices oblique • For spin echo sequences, the effect is smaller

  9. DBo

  10. Equipment available • 1.5 T Vision Siemens scanner head coil surface coil • Head holder device ear protection nose piece bite bar • Mirror and mirror stand • Mouse & joy stick • Trigger box • Projector cables RGB VGA screen • Physiological monitoring

  11. Accessories

  12. MR compatible mouse

  13. Penetration panel Inside the scanner room Outside the scanner room

  14. Screens

  15. Types of stimulation used at the MNI • Visual • Acoustic • Pain • Somatosensory • EEG

  16. Programs used for stimulus presentation • GLstim available on the SGI (R. Hoge ) • Media Control Function on PC (Windows) Pierre Ahad • SuperLab http://www.superlab.com • Make your own.

  17. Parameters for the protocol to be used

  18. Artifacts Patient wearing a metal studded belt Braces http://www1.stpaulshosp.bc.ca/stpaulsstuff/MRartifacts.html

  19. RF Artifacts

  20. Safety issues • Implants • Pacemaker • Metallic part left after surgery, or metallic fragments in their eyes • Belts • Tools (screw drivers, scissors, pens…) • Credit cards, bus pass. • Certain type of makeup, tattoos • Avoid loops

  21. Safety issues

  22. Safety issues contd..

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