DTI data acquisition uses "echo-planner imaging", with which you can get one 2D slice image with one shot. For example, if you have 128 x 128 matrix, it reads all 128x128 data points at once.<div><br></div><div>This is a rapid and high-SNR method, but the drawback is, the image distorts in the phase encoding direction, which is usually the front-back orientation</div>
<div><br></div><div>Depending on how you acquire the image, the images are either elongated or shrunk.</div><div>If the entire object get elongated or shrunk linearly (like a rubber band), the correction would be easy. However, such image distortion is localized along sinus and ear canals. That means, the distortion is like you pinch or push a cray object; they are localized. Anatomically, the frontal tip of the frontal lobe, the bottom of the temporal lobe, and the pons are the locations typically deformed. </div>
<div><br></div><div>For the frontal lobe, it gets pinched (exploded) or pushed in (imploded). Usually, if you use a default setting, Philips scanners give you the pinched appearance of the frontal lobe and the pons get pushed in. Siemens and GE are opposite.</div>
<div><br></div><div>Your second image seems to have imploded frontal lobe, while the first one gets exploded. That's my impression. I maybe wrong. If I'm right, you have to figure out why your second image has atypical imploded appearance. Somebody might have explicitly changed the direction of the phase encoding gradient.</div>
<div><br><div class="gmail_quote">On Fri, Jan 4, 2013 at 11:44 AM, Dorian P. <span dir="ltr"><<a href="mailto:alb.net@gmail.com" target="_blank">alb.net@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
They should be but can't say it for sure. They have both par/rec<br>
files, hence should be a Philips for both.<br>
<br>
What does the frontal implosion mean? I also read another comment from<br>
you, Dr. Mori, regarding different templates for different scanners:<br>
<a href="http://cmrm.med.jhmi.edu/cmrm/forumMRI/topic.php?id=63" target="_blank">http://cmrm.med.jhmi.edu/cmrm/forumMRI/topic.php?id=63</a><br>
<br>
I am simply using the single subject template, which I hope will bring<br>
any frontal implosion/explosion to the same space.<br>
<br>
Thank you.<br>
<br>
Dorian<br>
<br>
2013/1/4 susumu mori <<a href="mailto:susumu@mri.jhu.edu">susumu@mri.jhu.edu</a>>:<br>
> Are they from the same scanner?<br>
> First one has exploded frontal lobe, usually what you see with default<br>
> Philips scans.<br>
> Second one has imploded frontal lobe, usually with Siemens.<br>
><br>
> This is caused by the orientation of the phase-encoding steps; from positive<br>
> to negative gradients or from negative to positive gradients.<br>
><br>
><br>
><br>
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