[Mristudio-users] re： re： How to do a Tailarach transformation?

[jinsong tang]

Susumu, 

Thank you so much for your suggestions.

Best,

Jinsong




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发件人： susumu <susumu at mri.jhu.edu>
收件人： "DTI Studio, ROI Editor, Landmarker Questions/Support" <mristudio-users at mristudio.org>
已发送： 2009/4/8(周三), 上午1:36:27
主题： Re: [Mristudio-users] re： How to do a Tailarach transformation?


Hi Jinsong,
 
It depends on whom you ask the question, but here is my opinion.
 
When you are using diffusion “tensor” imaging, all data will be fitted to obtain only the 6 tensor elements. Therefore, you need only 6 directions mathematically. However, such measurement takes only less than 1 min and do not have enough SNR (signal-to-noise ratio). To enhance the SNR, you need to acquire more data.
 
Usually people spend 4-10 min of time for DTI, in which you can acquire about 30 – 100 images. Then you have several options. For example, you can repeat the 6-orientation measurement 5 times (total 30) or one 30-orientation measurement within the same amount of time (should be within 5 min). 
 
Purely from mathematical point of views, I don’t think 6-direction x 5 vs 30-orientation have that much difference in terms of overall SNR. However, it is true that the 6-orientation measurement has more orientation-dependent inhomogeneity in SNR. This means, certain orientations can be measured with higher SNR while some orientation has poorer SNR. By adopting more orientations, such orientation-dependent SNR profile becomes more homogeneous (less orientation dependent).
 
In reality, within practical imaging time, I don’t think you can observe such effect clearly. Our past measurement (Landman et al, NeuroImage) suggests once you have 12-orientation or more, you don’t see much differences.
 
Some researchers are seeking for diffusion “more than one tensor” imaging. If you want it, you may need more than 30 orientations and higher b-values. So, you may need to design very different protocols.
 
Susumu
 
 
 

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From:mristudio-users-bounces at mristudio.org [mailto:mristudio-users-bounces at mristudio.org] On Behalf Of jinsong tang
Sent: Tuesday, April 07, 2009 12:52 PM
To: DTI Studio, ROI Editor, Landmarker Questions/Support
Subject: [Mristudio-users] re：How to do a Tailarach transformation?
 
Hello everyone,
 
Now the Siemens  3.0 T MRI scanner can collect 30  non-collinear directions diffusion data. Does this helpful for fiber tracking ?
 
But I found most paper only use 12 directions. Does anybody know why?
 
Best,
 
Jinsong
 

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