xyz and z-score at peak of a cluster

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1

Hi everyone,

After using “Clusterize” and “Rpt” buttons to generate the table of clusters, I notice that the XYZ coordinates and Z score obtained for the peak of each cluster in the table is different for the following 2 cases:
(1) Click “Jump” to move to the peak of a cluster, then observe the Z score value shown at "Thr = … " on the bottom of the main GUI windows.
(2) I first click on “Write” to write out a dataset for the cluster, then run 3dExtrema with the cluster dataset as mask to output a few local maxima points, then I take the first point with highest Z score.
The Z score of the peak obtained from (2) is higher than that from (1).
And when moving to the XYZ coordinates obtained from (2), "Thr = … " really shows a higher value than (1).
I feel that I am missing something important here.
Could anyone please explain the difference.
My clusters are quite small, and the difference in terms of XYZ is just a few mm (still in the same atlas ROI), but I expect the peak should be the same for (1) and (2). (!?)

Thanks,
Duong

2

Hi Duong,

I would have to guess you are just seeing the effect of resampling in the GUI. If the underlay is a higher-resolution anatomy, then afni might resample the overlay to match it, which could result in shifting values and coordinates.

Set the underlay to be the same as the overlay and try again.

  • rick