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<div class="moz-cite-prefix">Hello<br>
<br>
Yes signal dropouts is a common feature of Siemens dti
acquisition. but it is not clear what is the exact cause. I think
there may be different cause<br>
_ subject motion (when there is a lot of subject motion then I see
several dropout on the same volume<br>
_ bed vibration a know problem on TRIO 3T (I heard they had a
solution but we could not convince them to install it ...)<br>
_ gradient heating<br>
_ partial fourier : Jesper on fsl list : " My personal experience
is for example that 5/8 is to severe and that 3/4 is better for
reducing drop-out."<br>
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</pre>
For the gradient heating you can try to increase the TR (take 1 or
2 second abouve the minimal TR ). The bvec order may also play a
role : make sure you the directions where the absolute amplitude
on a given axis (it is often the case)<br>
<br>
in the next mrtrix release there will be a correction for those
'bad' slice<br>
<br>
Cheers<br>
<br>
Romain<br>
<br>
Le 05/11/2013 15:13, Dorian P. a écrit :<br>
</div>
<blockquote
cite="mid:CAF9pfmZM4bfpJLqJaaDQXL2z_bsX_bMqoXmvu_kZCoYB9CWU3g@mail.gmail.com"
type="cite">
<div dir="ltr">Dear MRtrix list,
<div><br>
</div>
<div>My HARDI sequence is frequently contaminated by slices with
collapsed signal. This happens in 2-3 slices of 61 volumes.
Slices and volumes affected are a bit random, not always the
same.</div>
<div><br>
</div>
<div>In concomitance I see shifts in anterior-posterior (phase)
direction from one volume to the other. I have been told this
may happen because gradients heat to much.</div>
<div><br>
</div>
<div>My question at this point is:anybody had the same
experience with slice dropouts?</div>
<div><br>
</div>
<div>Do you think slice dropouts are related to the b-value.
Would decreasing b from 3000 to 2500 make a difference? Could
slices collapse because of motion causing bigger artifacts
with high b-values?</div>
<div><br>
</div>
<div>Finally, do you think the slice collapse is related to the
anterior-posterior shift (gradient heating) problem?</div>
<div><br>
</div>
<div>Any comment may be useful.</div>
<div>Thank you.</div>
<div><br>
</div>
<div>Dorian</div>
<div>TJU</div>
</div>
<br>
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</blockquote>
<br>
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