stimulus presentation and image acquisition

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Stimulus Presentation and Image Acquisition Valentina Petre

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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) - PowerPoint PPT Presentation

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Page 1: Stimulus Presentation and Image Acquisition

Stimulus Presentation and Image Acquisition

Valentina Petre

Page 2: Stimulus Presentation and Image Acquisition

How do we Design an Experiment

Event related

Block design

Page 3: Stimulus Presentation and Image Acquisition

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

Page 4: Stimulus Presentation and Image Acquisition

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

Page 5: Stimulus Presentation and Image Acquisition

Stim on

Slice i

Frame aq

Event Related stimulus presentation desynchronized from scanner acquisition

Page 6: Stimulus Presentation and Image Acquisition

Protocols available 128 x 128 64 x 64 Mosaic

Resolution

Signal to Noise

Time betw. Acq.

Max # of slices for 128 frames

Time to acquire one slice

Delay time

Excitation order

high

2.3 x 2.3 mm

low

long (~10 min)

16 slices with 3.5s TR

120-130ms

140-150ms

low

5 x 5 mm

high

short

27 slices with 3 s

TR

100ms

140ms

ProtocolProp

Interleaved

Ascending

Page 7: Stimulus Presentation and Image Acquisition

Small voxel volume, low signal Large voxel, high signal

Air tissue interface

Air

Tissue

The field inhomogeneity is large, thus it will cause large phase dispersion across the voxel. The signal is reduced.

Page 8: Stimulus Presentation and Image Acquisition

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

Page 9: Stimulus Presentation and Image Acquisition

Bo

Page 10: Stimulus Presentation and Image Acquisition

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

Page 11: Stimulus Presentation and Image Acquisition
Page 12: Stimulus Presentation and Image Acquisition
Page 13: Stimulus Presentation and Image Acquisition
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Accessories

Page 15: Stimulus Presentation and Image Acquisition
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MR compatible mouse

Page 18: Stimulus Presentation and Image Acquisition

Outside the scanner room Inside the scanner room

Penetration panel

Page 19: Stimulus Presentation and Image Acquisition

Screens

Page 20: Stimulus Presentation and Image Acquisition
Page 21: Stimulus Presentation and Image Acquisition

Types of stimulation used at the MNI

• Visual

• Acoustic

• Pain

• Somatosensory

• EEG

Page 22: Stimulus Presentation and Image Acquisition

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.

Page 23: Stimulus Presentation and Image Acquisition

Parameters for the protocol to be used

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Artifacts

Patient wearing a metal studded belt Braces

http://www1.stpaulshosp.bc.ca/stpaulsstuff/MRartifacts.html

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RF Artifacts

Page 28: Stimulus Presentation and Image Acquisition

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

Page 29: Stimulus Presentation and Image Acquisition

Safety issues

Page 30: Stimulus Presentation and Image Acquisition

Safety issues contd..