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help > RE: Calculating DVARS
Nov 15, 2020 08:11 PM | Alfonso Nieto-Castanon - Boston University
RE: Calculating DVARS
Dear Zahra,
The first-level covariate named 'QC_timeseries' (this is typically created during ART preprocessing step) contains two timeseries, the first is the Global Signal change timeseries, and the second is the Framewise Discplacement timeseries. These two timeseries are the ones that are: a) thresholded, in order to determine possible outlier scans; and 2) averaged to compute summary QC_MeanGSchange and QC_MeanMotion stats. That said, while similar, GSchange timeseries is not exactly the same as DVARS, since the former is computed as the absolute scan-to-scan difference of the across-voxels-average of the BOLD signal, while the latter is computed as the square root of the across-voxel-average of the squared absolute difference of the BOLD signal, so there is no one-to-one relationship/transformation between GSchange and DVARS.
Hope this helps
Alfonso
Originally posted by Zahra Mor:
The first-level covariate named 'QC_timeseries' (this is typically created during ART preprocessing step) contains two timeseries, the first is the Global Signal change timeseries, and the second is the Framewise Discplacement timeseries. These two timeseries are the ones that are: a) thresholded, in order to determine possible outlier scans; and 2) averaged to compute summary QC_MeanGSchange and QC_MeanMotion stats. That said, while similar, GSchange timeseries is not exactly the same as DVARS, since the former is computed as the absolute scan-to-scan difference of the across-voxels-average of the BOLD signal, while the latter is computed as the square root of the across-voxel-average of the squared absolute difference of the BOLD signal, so there is no one-to-one relationship/transformation between GSchange and DVARS.
Hope this helps
Alfonso
Originally posted by Zahra Mor:
Dear Conn experts,
Excuse my naive question!
How do we calculate DVARS (Power, 2012) in Conn?
I have the Mean GSchange as a 2nd level covariate, but can not figure out how to step back to each subject's global signal change. So then (maybe) I can use this subject level GSchange to calculate DVARS (?)
Thanks in advance!
Excuse my naive question!
How do we calculate DVARS (Power, 2012) in Conn?
I have the Mean GSchange as a 2nd level covariate, but can not figure out how to step back to each subject's global signal change. So then (maybe) I can use this subject level GSchange to calculate DVARS (?)
Thanks in advance!
Threaded View
| Title | Author | Date |
|---|---|---|
| Zahra Moradimanesh | Nov 10, 2020 | |
| Alfonso Nieto-Castanon | Nov 15, 2020 | |
| Nick Bray | Nov 10, 2020 | |
| Zahra Moradimanesh | Nov 10, 2020 | |
| Alex G | Nov 10, 2020 | |
| Zahra Moradimanesh | Nov 10, 2020 | |