We're testing an in-house sequence that applies z-shim compensations
only to selected slices, similar to what Du et al. (2007; MRM) have
used. The idea is to recover signal from OFC and amygdala without
increasing the overall TR markedly, by just applying the z-shim to the
areas most affected by artifacts.
However, this now results in some slices having a slightly longer
acquisition time than others, for example, inferior axial slices take
100 msec to acquire, whereas superior slices take only 66 msec to
acquire (sequence is interleaved on the Trio).
It isn't clear how to do slice-timing with unequal slice acquisition
times, or what other problems this may introduce -- all of the SPM
documentation seems to assume equal slice durations, yet it would seem
possible to modify this in the slice-timing routine.
Has anyone encountered this sort of issue before?
Thanks,
Stephan
Stephan Hamann
Department of Psychology
email: [log in to unmask]
http://www.socialtext.net/hamannlab
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