Dear SPMers,
I have two questions regarding ArtRepair and I would be very grateful if someone could help me.
First, when using art_global, a box comes up asking me for the realigned files. I have not resliced the files during realignment (the files are only resliced during normalization). Can I select the wa*.img files instead (ie, slice-timing corrected and normalized)?
>YES. Art_global will work with normalized images. It just needs to find the realignment files for each session (usually rp001.txt).
Second, is it still recommended to include the 6 motion parameters during the specification of the model at 1st level even if I use art_global?
>GENERALLY YES. There are two kinds of motion artifacts- rapid scan-to-scan motions that produce spin history artifacts and image distortions, and "large" motions where there is little scan-to-scan movement, but where the head is still displaced from the reference image that was used for realignment. Art_global detects the volumes with rapid motions and interpolates through them to suppress possible noise spikes on those volumes. But if the subject's head slowly drifted a 1 mm in translation, the displacement effect is still present and art_global will not detect it. Adding motion regressors will adjust for the displacement effect. The possible exception to using motion regressors is when there is substantial task-correlated motion, which can be issue in block design experiments.
- Paul Mazaika
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