One suggestion is to use >>art_movie to visually look at the
normalized, smoothed data that will be input to the GLM.
It is often helpful to compare the movie from a good data set and
the bad data set, to get a visual sense of what good data looks like.
If there are suspicious slices in the normalized smoothed data,
the same artifacts will often show up more clearly in the
data before any preprocessing.
There may be some bad slices in the data...the art_repair programs
cannot fix certain types of problems (e.g. the same bad slice on consecutive volumes).
A second suggestion is to use motion regressors in the design matrix,
if they are not already included.
Cheers,
Paul
----- Original Message -----
From: "Michael Treadway" <[log in to unmask]>
To: [log in to unmask]
Sent: Monday, April 20, 2009 11:46:02 AM GMT -08:00 US/Canada Pacific
Subject: [SPM] Artifact
Hi SPMers,
We have a first-level analysis for which several of our contrasts
have been showing "streaks" of activation (see attached image). We are
wondering if this pattern of activation could possibly result from
normal/benign variance, or whether it implies something seriously
wrong with either our data or preprocessing.
The motion for this subject was generally good (all runs < 1.2mm for
all 6 parameters). Preprocessing steps included ArtRepair bad slice
detection and bad volume detection.
Many Thanks,
Michael Treadway, MA
Department of Psychology
Vanderbilt University
301 Wilson Hall
111 South 21st Avenue
Nashville, TN 37203
610.909.2565
[log in to unmask]
--
Paul K. Mazaika, PhD.
Center for Interdisciplinary Brain Sciences Research
Stanford University School of Medicine
Office: (650)724-6646 Cell: (650)799-8319
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