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

[Seongjin]

Thanks a lot!
SC

2009/4/8 susumu <susumu at mri.jhu.edu>

>  Here it is.
>
>  ------------------------------
> *From:* mristudio-users-bounces at mristudio.org [mailto:
> mristudio-users-bounces at mristudio.org] *On Behalf Of *[Seongjin]
> *Sent:* Tuesday, April 07, 2009 10:31 PM
> *To:* DTI Studio, ROI Editor, Landmarker Questions/Support
> *Subject:* [Mristudio-users] Re: re£º How to do a Tailarach transformation?
>
> Dear Susumu,
>
> Do you have relevant literature on your opinion:
>
> "...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..."
>
> If you had, could you share the literature?
>
> Thanks.
>
> - SC
>
>
> 2009/4/7 susumu <susumu at mri.jhu.edu>
>
>>  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 ¨C 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
>>
>>
>>
>>
>>
>>
>>  ------------------------------
>>
>> *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£º 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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>>
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