F.C. Donders Centre for Cognitive Neuroimaging

1F.C. Donders Centre for Cognitive Neuroimaging

MR-Scanner

2F.C. Donders Centre for Cognitive Neuroimaging

MR-Scanner

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a) Protonen außerhalb des Magnetfeldes

N

Z

b) Protonen im Magnetfeld

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Components of MRI-scanner

Supergeleidendemagneet

Pulsprogramma

Rf zenderRf ontvanger

Gradiëntspoelen

Computersysteem

Rf antenne

Gradiëntversterkers

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Anatomische MR-Aufnahme

Angeregte Protonen kehren in verschiedenen Gewebearten (weisse, graue Substanz, Liquor) unterschiedlich schnell in den Ruhezustand zurück

160-180 sagittale Schichten Auflösung: 1 x 1 x 1 mm Dauer: +/- 10 Minuten

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Structural MR scan: sagittal slices

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radioaktives Wasser

HämoglobinSauerstoff

Blutstrom

Functionele MRI PET

Act

ieve

fas

eR

ust

fase

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Menon and Kim (1999)

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Blutfluss zu aktivem Hirngewebe nimmt stärker zu, als für die Sauerstofversorgung nötig

Sauerstoffsättigung des Hämoglobins im venösen Blut nimmt zu

Magnetische Störung durch venöses Blut nimmt ab

Angeregte Protonen drehen sich länger synchron. Ihr elektrisches Signal dauert länger/ist stärker.

Funktionelle MR-Aufnahme

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Data collection, fMRI

Terminology I– Volume = 1 brain image = 1 set of slices (typically 16-

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– Run = 1 set of volumes measured continuously (typically 80 – 120)

– Session = 1 set of runs without subject leaving the scanner (typically 2 – 16)

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Functional MR scan: 16

horizontal slices

(1 ‘volume’)

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Data collection, fMRI

Terminology II, Design types– Blocked = continous presentation of several stimuli of the same

type (advantage: stronger signal)– Event-related = measurement of response to single stimuli

(advantage: randomization possible, analysis can be based on behaviour)

– Measurement can be stimulus-locked (fixed temporal relation between stimulus and scan), jittered (average relation fixed but for every stimulus slightly varying), or temporally unrelated to the stimulus

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fMRI Design Options

BLOCKED:

SPACED EVENT-RELATED:

EVENT-RELATED:

MINI-BLOCKS: Instead of one event a small and varying number of events of the same condition

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TIME

TRANSIENT BOLDRESPONSETO EVENTS

MEASUREDBOLD

RESPONSE

SUSTAINED BOLDRESPONSE

TO SET

TIME

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Menon & Kim, 1999

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functional MR scan: movement correction

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PETPRONUNCIATION OF PSEUDOWORDS

vs.PRONUNCIATION OF WORDS

Hagoort, P., Indefrey, P., Brown, C., Herzog, H., Steinmetz, H., and Seitz, R.J. (1999).

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fMRIPSEUDOWORDS vs. WORDS

(0.001; 0.05 corr.)

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fMRISingle subject analyses: PSEUDOWORDS vs. WORDS

24Gazzaniga, Ivry, and Mangun (1998)

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Functional studies: PET – MR decision

Default: MR

Consider PET if:– ROI inferior temporal lobe– Overt continuous speech production during scans

necessary– High quality acoustic stimuli necessary– ERP registration during scans necessary– TMS during scans necessary– Claustrophobic subjects– Subjects with intracorporeal metal

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12 time series (runs) of 125 volumes, TR = 2338 sec

Encoding Delay Response

Stimulation protocol of one run

Words

Pseudowords

False font strings

Baseline (rest)

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‘What’-task

GRAGEL

BEURAL

DIESTE

BEURALyes

no

2 TR 6 TR 2 TR

TR=2338 ms

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GRAGEL

BEURAL

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BEURAL

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‘Where’-task

GRAGEL

BEURAL

BEURAL

BEURALno

yes

2 TR 6 TR 2 TR

TR=2338 ms

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BOLATI

DIESTE

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DIESTE

Delay

Encoding/Response

where

what

Delay

Encoding/Response

where

what

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non-verbal

verbal

Encoding period of ’what’-trials

p.orb

p.operc

MTG

ITG

lat.occ