fMRI Group
description
Transcript of fMRI Group
fMRI Group
Natasha Matthews, Ashley Parks, Destiny Miller, Ziad Safadi, Dana Tudorascu, Julia Sacher. Adviser: Mark Wheeler
Aims
Learn to implement block and event-related fMRI experimental designs
Develop a thorough understanding of the major choice points in the analysis stream for fMRI data
Learn fMRI data post-processing: GLM and group analysis
Block ER
Design
Pros: High detection power due to
response summation Simple analysis
Con:Can’t look at effects of single events
(e.g., correct vs. incorrect trials; target present vs. absent)
Pros: Good estimation of time courses and
reasonable detection Enables post hoc sorting (e.g.,
correct vs. incorrect; target present vs. absent)
Con: Some loss of power for the contrast
between trial types.
Task: Median Nerve Stimulation
A nerve stimulation device is place on the subjects wrist above their median nerve
An electrical pulse is applied, resulting in activation of the nerve
Data AcquisitionScanner : Siemens 3T Trio
Number of subjects: 3
Anatomical Scan
T1 (MPRAGE)Slices : 38Functional Scan (Block design)
Whole Brain ScanSlices : 38Volumes:144
Voxel Size : 4 mm x 4 mm x 3.2mmInterleaved AcquisitionTR : 2sT2* Contrast
Scanner : Siemens 3T Trio
Number of subjects: 3
Anatomical Scan
T1 (MPRAGE)Functional Scan (Event-related design)
Whole Brain ScanSlices : 38Volumes run 1: 256Volumes run 2: 256Voxel Size : 4 mm x 4 mm x 3.2mmInterleaved AcquisitionTR : 2sT2* Contrast
Scanner : Siemens 3T TrioNumber of subjects: 3
Anatomical Scan
T1 (MPRAGE)Slices : 38Voxel Size: 0.5mm x 0.5mm x 1.0mm
Blocked Design
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Time 0 s……....……….22s…….32s…………54s……64s…………86s……..96s……………. …278s Task
Volumes……………….11.…….16..…….……27.……32..…………43.……...48.……………. …139 (+5 extra)
Rest Rest Rest Rest
ZAP ZAP ZAP
Median Nerve Stimulation Localizer Task DesignGoal: Determine Motor Cortex Activation Region for Event
Related Task
Nerve Stimulation Localizer Task
Data Preprocessing for individual subjectsData Format: convert scanner images to format readable by AFNI
Dicom data, reformat to BRICK & .HEAD
Time Shift (slice timing correction): interpolation of time series to a specific point in TR (Fourier transformation: most accurate).
Spatial Registration (motion correction): of all images in the time series to a base image: we chose 6th image of run (close to structural image).
Smoothing: We investigated 4mm, 8mm, 12mm.
Spatial Smoothing
Box-car Model
Model Fit: No smoothing
Model Fit: 4mm smooth
Model Fit: 8mm smooth
Model Fit: 12 mm smooth
t-statistics in individual voxels in ROI
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Nopreprocessing
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41.36.27
44.37.29
Beta coefficients in individual voxels in ROI
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Nopreprocessing
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44.37.29
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Data Preprocessing: Preparing for group analysis
Normalize time series: Regression coefficients now expressed as % signal change. For each run divide each time point by the mean and multiply by 100.
Original data Normalized data
Preparing data for group analysis
Registration to standard space: Can be done manually or automatically
Atlas TemplatesTT_N27+tlrc: AKA “Colin brain”. One subject (Colin) scanned 27 times and averaged.
TT_avg152T1+tlrc: Montreal Neurological Institute template, average volume of 152 normal brains.
Group t-test (zap > baseline)
Event-related Design
Event Related Design: Stimulation with 3 different frequencies
2 Hz
3.85 Hz
9 Hz
Zap ON 9.09 3.85 2.00
Inter-stimulus jitter - 2, 4, 6 seconds
Data from a representative subject2 Hz 3.8 Hz 9 Hz
Comparison of 9 Hz Event Related Design and Block Design
Bloc
k de
sign
Even
t rel
ated
des
ign
Creation of ROI masks to explore event-related data
ROI from functional results (localizer task)
ROI based on atlas coordinates
Time courses extracted from functionally defined ROI
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Time
Beta values
average_9Hzaverage_4Hzaverage_2Hz
Peak of the activation
Area under the curve
Results of ANOVA on event related datausing the PEAK of the time course
Results of ANOVA on event related datausing the AREA UNDER THE CURVE
Thank you
Mark WheelerSeong-Gi KimTomika CohenRebecca Clark
Fellow MNTPers!