Greetings,
I'm trying to write a script to generate hemodynamic timecourses for particular voxels. I want to imitate the feature in tkmedit where these graphs can be viewed as Percent Signal Change.
I know how to generate this for averages across an ROI, but that involves computing the Average Baseline Activity, a quantity which is tied to the size ROI and thus does not make sense to use for a single voxel.
Does anyone know what value is used to properly scale the hemodynamic timecourses and how to compute that value?
Thanks
Matt Cain mcain@nmr.mgh.harvard.edu
What I do in "froi" is take the value at the particular voxel and divide by the h-offset value for that voxel and multiply by 100. For ROIs, that's done individually for each voxel, and then averaged to get the value for the ROI.
To get the standard deviation is similar, except of course you can't simply average standard deviations, but rather I compute the variance for each voxel, average the variances together, and then compute the standard deviation.
The standard error is more complicated but I can give you more info if you'd like.
nick
On Jun 16, 2004, at 3:24 PM, Matt Cain wrote:
Greetings,
I'm trying to write a script to generate hemodynamic timecourses for particular voxels. I want to imitate the feature in tkmedit where these graphs can be viewed as Percent Signal Change.
I know how to generate this for averages across an ROI, but that involves computing the Average Baseline Activity, a quantity which is tied to the size ROI and thus does not make sense to use for a single voxel.
Does anyone know what value is used to properly scale the hemodynamic timecourses and how to compute that value?
Thanks
Matt Cain mcain@nmr.mgh.harvard.edu
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
Thanks for the suggestions. I'm trying to read in the h-offset volumes, but I can't figure out the correct matlab script to use. To read in the h volumes I'm using fast_ldsxabfile, but that assumes there is a file <stem>.dat and there's no h-rh-offset.dat. I could probably hack something together, but this sounds like a problem that's probably ben solved before...
-Matt
On Jun 16, 2004, at 16:14, Nick Knouf wrote:
What I do in "froi" is take the value at the particular voxel and divide by the h-offset value for that voxel and multiply by 100. For ROIs, that's done individually for each voxel, and then averaged to get the value for the ROI.
To get the standard deviation is similar, except of course you can't simply average standard deviations, but rather I compute the variance for each voxel, average the variances together, and then compute the standard deviation.
The standard error is more complicated but I can give you more info if you'd like.
nick
On Jun 16, 2004, at 3:24 PM, Matt Cain wrote:
Greetings,
I'm trying to write a script to generate hemodynamic timecourses for particular voxels. I want to imitate the feature in tkmedit where these graphs can be viewed as Percent Signal Change.
I know how to generate this for averages across an ROI, but that involves computing the Average Baseline Activity, a quantity which is tied to the size ROI and thus does not make sense to use for a single voxel.
Does anyone know what value is used to properly scale the hemodynamic timecourses and how to compute that value?
Thanks
Matt Cain mcain@nmr.mgh.harvard.edu
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
freesurfer@nmr.mgh.harvard.edu
-
Matt Cain -
Nick Knouf