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MR-Scanner. F.C. Donders Centre for Cognitive Neuroimaging. MR-Scanner. F.C. Donders Centre for Cognitive Neuroimaging. b) Protonen im Magnetfeld. N. a) Protonen au ßerhalb des Magnetfeldes. Z. Gradiëntspoelen. Rf antenne. Components of MRI-scanner. Supergeleidende magneet. Rf - PowerPoint PPT Presentation
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1F.C. Donders Centre for Cognitive Neuroimaging
MR-Scanner
2F.C. Donders Centre for Cognitive Neuroimaging
MR-Scanner
3
4
a) Protonen außerhalb des Magnetfeldes
N
Z
b) Protonen im Magnetfeld
5
Components of MRI-scanner
Supergeleidendemagneet
Pulsprogramma
Rf zenderRf ontvanger
Gradiëntspoelen
Computersysteem
Rf antenne
Gradiëntversterkers
7
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-
24)
– 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