Dear SPMers,
We would like to
compare patients who have participated in two sessions of the same PET paradigm,
while they were treated or not treated with
a pharmacological treatment. Sessions were separated by 8 weeks.
The order of
sessions was counterbalanced, with 5 subjects in a treated - untreated order,
and 5 subjects in untreated - treated
order.
We have 6 experimental conditions (with 2
replications, i.e, 12 scans/subject/session):
cond 1:
N
cond 2:
H
cond 3:
A
cond 4: B
cond 5: C
cond 6:
S
In each session,
our contrasts of primary interest are: S -N; S-H and C-A.
We want to test the effect of the pharmacological
treatment on the rCBF responses to the stimuli (for example, compare S-N when
treated with S-N when
untreated).
In a message from
K. Friston (07/13/2001; session effect), he said that it was possible to
"specify the number of sessions", but we don't see this
option in SPM99 for PET. Is it fMRI specific? if yes, how can we take advantage
to the fact that we have the same subjects in the 2
sessions?
Another problem
is that we think that the treatment may have an effect on the global cerebral
blood flow. If we compare scans between treatment
conditions, the differences may be then due to this factor. What is the method
to correct this problem?
Finally, when
assessing the main effect of treatment (irrespective of experimental conditions,
is it correct to use the contrast -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 (the first
6
terms represent the 6 untreated experimental
conditions, the second six terms
represent the 6 treated experimental conditions) in a
single-group/multi-subjects/conditions and covariates
model?
Thank you.
J.R.
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Jérôme REDOUTE
CERMEP
Hôpital Neuroogique
59, Bd Pinel. 69003 LYON
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