Dear Ruth,
>Best New Year's greetings to all SPM-helpers!
>
>
>My question relates to the interpretation of the numerical values given for
>"fitted and adjusted response" in SPM-plot.
>
>After making an extensive search of SPM archives, I find that for PET
studies,
>the question has not been clarified.
>
>From the message below, I copy the section of current interest:
>
> Alex: In which units is the response plotted?
>
> Karl: If you have used scaling normalization (with a grand mean of
100)
> the units are adimensional and correspond to percentage of whole brain
> mean.
>
>
>The question is, how to interpret the "response" when plotting fitted and
>adjusted values from a PET study where grand mean = 50 and subject-specific
>ANCOVA scaling was employed? If I understand correctly, "percent change"
is
>not relevant here. How shall we identify the units of measurement in the
graph?
>
The value of 50 for (rCBF) PET was choosen since 50 (ml/(min*100ml)) is
approximately the whole brain mean of CBF that was found when measuring it
quantatively (demands arterial line). Hence, when measuring rCBF
qualitatively (i.e. obtain a map lineraly related to CBF) the scaling to 50
scales the values approximately to ml/(min*100ml).
>Thanks for your advice,
>
>Ruth Reinsel
>
Good luck Jesper
Jesper Andersson
Wellcome Dept. of Cognitive Neurology
12 Queen Square
London WC1N 3BG
phone: 44 171 833 7484
fax: 44 171 813 1420
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