[Mristudio-users] How to combine DTI data from different runs

[susumu mori]

Hi Darren,

In a previous communication in the mailing list, I explained why we can not
use regular k-space averaging for DTI and, therefore, we average data after
magnitude calculation (we average images, not k-space data). If anybody
remembers which thread it was, I would appreciate it.

Anyway, because we first have to calculate image before averaging, there is
no point to ask scanners to do the averaging. One downside of the
averaging-by-the-scanner is, if the images are mis-registered or there are
corrupted images, we can not undo the averaging.

I believe that is why Siemens always save all images separately (without
creating an "averaged image" even if multiple averaging is specified.

Please note the difference between "repeated scans (you submitted the same
protocol twice)" and "averaged scans (you specified 2 signal averaging)"
when you use Siemens. Either way, all images are saved individually and they
are basically the same studies. However, in the former case, the "repeated
images" are stored in different directories and Siemens console can not
combine them for DTI  calculation. With the latter case, the repeated images
are stored in the same directory and Siemens console can combine them to
calculate one DTI data.

Either way, when you use DtiStudio, you need to load all files at once and
DtiStudio can combine them to calculate one DTI.

Now going back to your question;

1) You can specify the number of signal averaging in Siemens. I'm not sure
why you thought you couldn't. However, if you meant, "Siemens saved all
images separately without averaging", then you are correct.
2) DtiStudio can read repeated scans and combine them for one DTI
calculation.

On Sun, Feb 28, 2010 at 7:54 PM, Darren Gitelman <
d-gitelman at northwestern.edu> wrote:

> Hello:
>
> Is there a way to combine data across several repeats of a DTI sequence?
>
> The reason I ask is that we have a Siemens Trio scanner but are
> working with another group that has a GE scanner. On the GE scanner
> the DTI sequence allows NEX > 1 (they are getting 4), which appears to
> improve their SNR considerably. The Siemens sequences do not allow
> this, so we are repeating the DTI sequence several times, and want to
> combine the data across runs. Can this be done within DTIstudio or
> some other program? Would it be best to do this at the level of the
> DTI images or the FA maps?
>
> Thanks,
> Darren
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