Hi Li Bei,
I recommend you to read a mail from Will Penny written two days ago. The
messsage name is just "[SPM]".
If you have two conditions, c1 and c2 and you want to see whether c1 is greater
than c2 then you should 'build' a [1 -1] t-contrast. However, if you want to
see whether c2>c1 then you would build a [-1 1] t-contrast (provided c1 is the
first condition in the design matrix, c2 the second).
If you build an F contrast like [1 -1] it will test whether there are
differences between c1 and c2, that is, c1>c2 and also c2>c1. That's why you
see differences between a t and an F contrast.
Cheers
Juan J
Cita de Li Bei <[log in to unmask]>:
> Dear Sir:
>
> I want to get the active regions so I define
> t-contrast with weight vector [1 -1],and define
> F-contrast with the same vector ([1 -1]).The result of
> T-constrast and F-contrast is different,why?
> (1)could you explain the difference between T-contrast
> and F-contrast and how to define weight vector for
> both F and T contrast in detail ?
> (2)will result incorrect if i define VOI with
> t-contrast and analyse those VOIs in DCM??
>
>
> Thank you!
>
>
>
> =====
> Bei Li
> Institute of Neuroinformatics
> Dalian University of Technology
> 2 Ling Gong Rd, Dalian 116023, China
> Email:[log in to unmask]
>
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________________________________________________________
Juan José Lull Noguera - jualulno_at_upvnet.upv.es
[MI - Medical Imaging Area]
BET - Bioengineering, Electronics and Telemedicine Group
UPV - Politechnical University of Valencia - Spain
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