fmri: biological basis and experiment design lecture 17: baselines, snr & cnr visualizing data...
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![Page 1: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/1.jpg)
fMRI: Biological Basis and Experiment DesignLecture 17: Baselines, SNR & CNR
• Visualizing data• Trial triggered
average• Baselines• SNR and CNR
– Block vs. ER
1 light year = 5,913,000,000,000 miles?
![Page 2: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/2.jpg)
Localizers scans define ROI
![Page 3: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/3.jpg)
Sample data – selected voxels, impulse response
Subject 3
Subject 4
Subject 2
Subject 1
voxe
l
time (seconds ... scans concatenated)
Scan 1 Scan 2 Scan 3 Scan 4
![Page 4: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/4.jpg)
Sample data – ROI average
Subject 3
Subject 4
Subject 2
Subject 1
voxe
l
time (seconds ... scans concatenated)
Scan 1 Scan 2 Scan 3 Scan 4
![Page 5: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/5.jpg)
Sample data – response average (60 trials)
Subject 3
Subject 4
Subject 2
Subject 1
time (seconds)
![Page 6: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/6.jpg)
Sample data – response average (30 trials)
Subject 3
Subject 4
Subject 2
Subject 1
time (seconds)
![Page 7: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/7.jpg)
Sample data – response average (15 trials)
Subject 3
Subject 4
Subject 2
Subject 1
time (seconds)
![Page 8: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/8.jpg)
Effect of averaging
Subject 3
Subject 4
Subject 2
Subject 1
NM
Error bars are S.E.M. (M)
![Page 9: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/9.jpg)
Analyzing each scan separately
Subject 3
Subject 4
Subject 2
Subject 1
![Page 10: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/10.jpg)
Baselines and contrasts
20s block cycles 10s block cycles
![Page 11: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/11.jpg)
Trade-off between CNR and block length
20s block cycles, 40 repetitions
10s block cycles, 80 repetitions
More contrast, fewer samples
Less contrast, more samples
![Page 12: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/12.jpg)
Signal-to-noise ratio
• Thermal noise– white– independent of voxel size– independent of tissue type– independent of voxel location– trivial with 3 x 3 x 3mm voxels– a problem with 1.5 x 1.5 x 1.5 mm voxels (1/8th volume)– for the sake of argument:
• SNRthermal,3mm = 160
• SNRthermal,1.5mm = 20
![Page 13: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/13.jpg)
SNRthermal: block and ER design
![Page 14: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/14.jpg)
Contrast-to-noise ratio: block and (slow) ER design
2.10083.0
01.0
3.70083.0
06.0
ER
ERER
block
blockblock
N
CCNR
N
CCNR
2.10083.0
01.0
ER
ERER N
CCNR3.7
0083.0
06.0
block
blockblock N
CCNR
![Page 15: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/15.jpg)
Response estimate: single voxel (SNR = 120)
![Page 16: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/16.jpg)
Sample data – block experiment
Scan 2Scan 1
time (seconds ... 2 scans concatenated)
voxe
l
ROI average predicted from HIRF
![Page 17: FMRI: Biological Basis and Experiment Design Lecture 17: Baselines, SNR & CNR Visualizing data Trial triggered average Baselines SNR and CNR –Block vs](https://reader036.vdocuments.net/reader036/viewer/2022062516/56649d3f5503460f94a185cb/html5/thumbnails/17.jpg)
Block response estimated with different HIRFsHIRF HRF