Dianne,
Generally, presents of negative FA values indicate a problem in alignment
among images of different directions.
It is expected to see them on the peripheral contour of the brain where
misregistration will be most apparent. However, if you see them trough out
the brain, your studies might not have been aligned well or you have a
problem with one or more direction images.
pk
----- Original Message -----
From: "Hedok Lee" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, December 05, 2007 2:35 PM
Subject: Re: [FSL] FA values greater than 1
> Dear Dianne:
>
> You can get FA above 1 when you have negative eigenvalues.
>
> Examples:
>
> The numbers are listed in the ordered of eigenvalue 1,2,3, mean, and FA.
>
> 500 500 -500 167 1.16
> 500 400 700 533 0.28
> 500 -200 300 200 1.01
>
> I typically ignore them. Others may have different opinions.
>
> Hope this helps,
>
> Hedok
>
> Dianne Patterson wrote:
>> Hello All,
>>
>> We have seen some values over 1 in our FA images...mostly these are
>> around the edges, but sometimes they are in the brain.
>> I know there was mention of this on the archives...and the suggestion was
>> that it wasn't a problem...
>>
>> But I am concerned...how do we end up with these high values?
>> Should they be thresholded out before further image processing?
>>
>> Is FSL unique in producing these high FA values?
>>
>> Any more information about the topic and/or suggestions about how to
>> handle it would be appreciated.
>>
>> Thankyou,
>>
>> Dianne
>>
>>
>>
>> --
>> Dianne Patterson, Ph.D.
>> [log in to unmask] <mailto:[log in to unmask]>
>> ERP Lab
>> University of Arizona
>> 621-3256 (Office)
>
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