[Mristudio-users] Why deleting b0 from one of the runs increases FA a lot.

[Susumu Mori]

Do you mean, you used different gradient tables for different runs?
I wonder if the gradient table and images are not matched for a part of
data.
Suppose you have 1 b0 + 12 DWIs x 2 runs and you lost one b0 in the second
run.
The only way to analyze this data, I can think of, is, combine the two runs
as 1 b0 + 12 DWIs + 12 DWIs and crate one 25-element gradient table.

In general, if you have less data, you have lower SNR and FA goes up but I
doubt if the loss of one b0 could cause such a large FA increase.


On Fri, Sep 27, 2013 at 10:38 AM, Dorian P. <alb.net at gmail.com> wrote:

> Dear developers and Dr. Mori,
>
> I am comparing FA for some tracts at two time points. At each time point I
> acquire 2-3 DTI runs to increase SNR. However, the scanner has
> malfunctioned for one of the runs in one subject. As a result the B0 image
> is not saved, but all other DWIs are there. So, I set the collapsed B0 to
> gradient 100, 100, 100 and align all DWIs to the only B0 available. For
> some results, the resulting FA is increased a lot.
>
> I tried the same procedure with another subject, when I set one of the B0
> to gradient 100, 100, 100, the resulting FA of the tract goes up from 0.51
> to 0.62.
>
> Is there any explanation why this is happening, and whether I should
> delete completely the collapsed B0 instead of setting it to 100, 100, 100?
>
> Thank you.
> Dorian
> TJU
>
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