The problem is with the function you use to fit the signal intensity.
If you make the fitting iterative, then it should be possible to deal
with negative values in the data by maximising the likelihood.
It's been a while since I looked at the attached code, but I think it
may do what you want (if the right info is in the image headers).
Have it checked out by someone who knows how to program first though.
As ever with bits of code sent by email, there is no guarantee that it
will work.
Best regards,
-John
On 23 June 2011 12:54, SUBSCRIBE SPM Shangwenyan Gong
<[log in to unmask]> wrote:
> Hello, Everyone,
>
> Sorry take your time! I have one problem due to negative signal intensity after SPM motion correction.
>
> I am doing t2* map of brain. And my first step is pre-processing of raw data (signal intensity). After SPM motion correction (realignment and reslice), I found negative signal intensity generated. And these negative signal intensity will cause complex t2* values, but t2* values should be at least real. Thus my t2* map will contain a lot of artifacts.
>
> So I wish to ask how to deal with these negative signal intensity? I do not know if I can introduce an offset to make negative values become positive, IF I can, how big the offset should I use?
>
> Thank you!
>
> Shangwenyan Gong
>
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