Hi HCP workbench folks, I’m trying to perform a particular calculation on a resting state data set using wb_command and, if possible, would like some advice on how to go about it most directly.
I’d like to compute the magnitude of a gradient at each point (voxel/vertex) on a surface and volume for a case in which each voxel/vertex corresponds to a vector valued function. To be explicit consider a volumetric data set V(x,y,z,t), where x,y,z are spatial coordinates and t is a time point. This could be just a typical resting state scan. Let 0 ≤ t ≤ m, where m is the last time point. For a given location, x0, y0,z0, the magnitude of the partial vector derivative dV/dx is given by: note: vector magnitudes are denoted by || || and is just a typical L2 norm || dV/dx || = || V(x0+dx ,y0 ,z0, t=0,1,2,….t=m) - V(x0, y0, z0, t=0,1,2,….t=m) || This is basically the magnitude of the vector difference of time series for two adjacent voxels It would appear that the workbench command -cifti-gradient is the appropriate starting place, but it is unclear how the command should be set up since computing the L2-norm would require calculating the sum-of-squares of the differences across all time points and the only option that I see is available is -average-output which would not serve my purpose if would simply perform the arithmetic mean across the time points if the difference This would be a relatively easy thing to implement in volume space, but I’d like to take advantage of working in surface-land for all of the usual reasons. Can you advise on what would be the most straightforward way to perform the calculation for || dV/dx || as outlined above. Many thanks! David Montez ________________________________ The materials in this message are private and may contain Protected Healthcare Information or other information of a sensitive nature. If you are not the intended recipient, be advised that any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this email in error, please immediately notify the sender via telephone or return mail. _______________________________________________ HCP-Users mailing list HCP-Users@humanconnectome.org http://lists.humanconnectome.org/mailman/listinfo/hcp-users
