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1 F.C. Donders Centre for Cognitive Neuroimaging MR-Scanner.

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Präsentation zum Thema: "1 F.C. Donders Centre for Cognitive Neuroimaging MR-Scanner."—  Präsentation transkript:

1 1 F.C. Donders Centre for Cognitive Neuroimaging MR-Scanner

2 2 F.C. Donders Centre for Cognitive Neuroimaging MR-Scanner

3 3

4 4 a) Protonen außerhalb des Magnetfeldes N Z b) Protonen im Magnetfeld

5 5

6 Components of MRI-scanner Supergeleidende magneet Pulsprogramma Rf zender Rf ontvanger Gradiëntspoelen Computersysteem Rf antenne Gradiëntversterkers

7 7 Anatomische MR-Aufnahme l Angeregte Protonen kehren in verschiedenen Gewebearten (weisse, graue Substanz, Liquor) unterschiedlich schnell in den Ruhezustand zurück l sagittale Schichten l Auflösung: 1 x 1 x 1 mm l Dauer: +/- 10 Minuten

8 8 Structural MR scan: sagittal slices

9 9 radioaktives Wasser Hämoglobin Sauerstoff Blutstrom Functionele MRIPET Actieve fase Rust fase

10 10 Menon and Kim (1999)

11 11 l Blutfluss zu aktivem Hirngewebe nimmt stärker zu, als für die Sauerstofversorgung nötig l Sauerstoffsättigung des Hämoglobins im venösen Blut nimmt zu l Magnetische Störung durch venöses Blut nimmt ab l Angeregte Protonen drehen sich länger synchron. Ihr elektrisches Signal dauert länger/ist stärker. Funktionelle MR-Aufnahme

12 12 Data collection, fMRI l Terminology I – Volume = 1 brain image = 1 set of slices (typically ) – Run = 1 set of volumes measured continuously (typically 80 – 120) – Session = 1 set of runs without subject leaving the scanner (typically 2 – 16)

13 13 Functional MR scan: 16 horizontal slices (1 ‘volume’)

14 14 Typische funktionelle MR-Messung l 125 Messungen von 16 horizontalen Schichten in einer Messperiode (Run) l TR (time to repeat) = 2338 ms Dauer zwischen zwei aufeinanderfolgenden Messungen derselben Schicht l Auflösung: x x 5.5 mm l 12 Runs

15 15 Data collection, fMRI l 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

16 16 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

17 17 TIME TRANSIENT BOLD RESPONSE TO EVENTS MEASURED BOLD RESPONSE SUSTAINED BOLD RESPONSE TO SET TIME

18 18 Menon & Kim, 1999

19 19

20 20 functional MR scan: movement correction

21 21 PET PRONUNCIATION OF PSEUDOWORDS vs. PRONUNCIATION OF WORDS Hagoort, P., Indefrey, P., Brown, C., Herzog, H., Steinmetz, H., and Seitz, R.J. (1999).

22 22 fMRI PSEUDOWORDS vs. WORDS (0.001; 0.05 corr.)

23 23 fMRI Single subject analyses: PSEUDOWORDS vs. WORDS

24 24 Gazzaniga, Ivry, and Mangun (1998)

25 25 Functional studies: PET – MR decision l Default: MR l 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

26 26 12 time series (runs) of 125 volumes, TR = 2338 sec EncodingDelayResponse Stimulation protocol of one run Words Pseudowords False font strings Baseline (rest)

27 27 ‘What’-task GRAGEL BEURAL DIESTE BEURAL yes no 2 TR6 TR2 TR TR=2338 ms

28 28 GRAGEL BEURAL

29 29 BEURAL

30 30 ‘Where’-task GRAGEL BEURAL no yes 2 TR6 TR2 TR TR=2338 ms

31 31 BOLATI DIESTE

32 32 DIESTE

33 Dela y Encodin g/Respo nse wher e wha t

34 Dela y Encodin g/Respo nse wher e wha t

35 35 non-verbal verbal Encoding period of ’what’- trials p.or b p.oper c MT G ITG lat.occ


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