[Mristudio-users] Gradient table

[susumu]

Yes. That's the idea. 

One thing you have to be careful is, if you have repeated dataset, like 3
sets of 12-orientation measurements.

After AIR, each DWI could be rotated in a different way and therefore obtain
a new gradient orientation.

That means, the 3 repeated measurements may no longer have the same
12-orientation gradient table. Instead, you will get 36 orientations.
Therefore, you have to combine all 3 sets to create one measurement with 36
orientations and your gradient table also has to be one 36-orientation
table.

 

Is this correct, Hangyi?

 

In DtiStudio, you can create average and subtracted images of repeated
measurements using the "mean, STD" button. From these images, you can get
idea about how much translation and rotation occurred during the scans.
Usually, the rotation is very tiny, like within 1 degree. In this case, you
don't have to use gradient table rotation, in my opinion. Unless you have a
bad data in which subject was moving more than few degrees, this rotation
correction may not have much importance. On the other hand, if the subject
is moving around, you may have other issues like image corruptions and
motion within one image (odd and even slices are not registered), which can
not be solved by AIR.

 

So, I guess what I'm saying is you should carefully inspect your data,
instead of just throwing your data into AIR, do gradient table rotation, and
forget about it.

 

  _____  

From: mristudio-users-bounces at mristudio.org
[mailto:mristudio-users-bounces at mristudio.org] On Behalf Of [Seongjin]
Sent: Thursday, April 30, 2009 3:32 PM
To: DTI Studio, ROI Editor, Landmarker Questions/Support
Subject: Re: [Mristudio-users] Gradient table

 

After AIR registration (with option modified gradient table if
available...), I have a new gradient table in AirMatrix.txt file.
Then I loaded AIR registered image and the new gradient table for tensor
calculation and tractography. 
Am I doing right?
Thanks in advance.

-SC

On Thu, Apr 30, 2009 at 1:18 PM, susumu <susumu at mri.jhu.edu> wrote:

The gradient table for Philips scanner calculated by this program is
"correct", meaning no flipping and other modifications are necessary.

 

I strong encourage users to use this program if you are using the "overplus"
option + oblique slice. You can type in the oblique angles and get a
recalculated table.

 

  _____  

From: mristudio-users-bounces at mristudio.org
[mailto:mristudio-users-bounces at mristudio.org] On Behalf Of [Seongjin]
Sent: Thursday, April 30, 2009 12:28 PM
To: DTI Studio, ROI Editor, Landmarker Questions/Support
Subject: [Mristudio-users] Gradient table

 

I appreciate the tutorial session at Queen's Medical Center in Honolulu.

I am using gradient table (for DTI studio ) generated at the following link:
http://godzilla.kennedykrieger.org/~jfarrell/OTHERphilips/GUI.html
<http://godzilla.kennedykrieger.org/%7Ejfarrell/OTHERphilips/GUI.html> 

I wonder if I can directly use the gradient table from this java applet
without field flipping.
Thanks in advance.

-SC


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