[Mristudio-users] tensor calculation - automatic outlier rejection

Tue Sep 16 10:45:31 EDT 2008

Dear Dr.Mori,

Thank you very much for your kind information. 

Thanks again,

Regards
venkateswaran

________________________________

From: mristudio-users-bounces at mristudio.org on behalf of susumu
Sent: Fri 9/5/2008 1:25 PM
To: 'DTI Studio, ROI Editor, Landmarker Questions/Support'
Subject: Re: [Mristudio-users] tensor calculation - automatic outlier rejection

Hi Venkateswaran,

The outlier rejection is still work-in-progress. We are about to post Version 3, in which there will be only one threshold to simplify the function. Meanwhile please use very large numbers for all thresholds to avoid the software to reject any images. 

However, there are two very handy functions in "verify the results" section of the window, which are two checkboxes with "create images of ,,,,".

After the calculation, please click the "Original-ADC-Mean-STD" button. In this window, you can see your raw data and "theory image", which tells how the image should look like calculated from all data, and "error image", which is the difference between the raw and theory data. These images can be very informative to detect corrupted images, typically observed around the forth ventricle (brainstem, cerebellum, and often up to the splenium of the corpus callosum). For the corrupted images, you can simply click the bad image and large red X mark appears. These images won't be included for tensor calculation. 

In our experience, maybe well more than 50% of DTI data do not have significantly corrupted images and you don't need to worry. There are, however, sometimes subjects who have several corrupted images. Once affected, it is common to see multiple severely corrupted ones. My experience says pediatric brains are more prone to the artifacts. There are sometimes signal leak from outside MRI that causes a spike in the k-space and produce "zebra" patterns. This should also be eliminated. 

The "error images" also sensitively detect subject motions and eddy current issues. These problems appear as a ring around the brain. If the subject moved in the middle of the scan, half the error images show bright edge in one side of the brain and dark edge in the other side. The rest of the images have the same edges but with the opposite bright/dark edge locations.

You can try different threshold levels to see if the software can automatically detect the one you thought bad. The version 3 has better automatic detection, but these functions are still beta.

Hope this helps.

Susumu

________________________________

From: mristudio-users-bounces at mristudio.org [mailto:mristudio-users-bounces at mristudio.org] On Behalf Of Rajagopalan, Venkateswaran
Sent: Friday, September 05, 2008 12:50 PM
To: mristudio-users at mristudio.org
Subject: [Mristudio-users] tensor calculation - automatic outlier rejection

Dear All,

Recently i downloaded latest version of DTI studio. When i tried to do Tensor calculation the usual DTI- map options appear first and when fill in the details and say ok another window pops up asking for outlier rejection and when i say yes another window pops up where there are many options to fill in.  It will be of great help to me if  anyone could please tell me what this new automatic outlier rejection option is for and where i can get details regarding how to choose these different options and under what circumstances should i go for this as i couldn't  find their details in the manual.

Thanks

venkateswaran

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