Dear FSL Experts,
we are planning to study the influence of four different context factors on the resting state signal (within subject design). I was wondering how to organize the paradigm with respect to the shimming procedure to ensure field homogeneity.
1 One option is to organise the scanning session in four separate (9 min) runs applying a different context factor during each run (=4 experimental conditions per subject). Before each run there is an automatic shim.
2 The alternative is to acquire all 4 experimental conditions in a sinlge run shimming only once instead of shimming before each separate run (the way 'task' fmri is typically done)
Maybe 2) is better because shimming before each run might introduce a bias to each condition (shimming may not produce identical 'homogeneous' fields ?)
Based on your experience which design would you suggest ?
Thanks a lot!
andi
