[Mristudio-users] Counterintuitive LDDMM results

[Dorian P.]

Ahh, I didn't know the kimaps should be combined. I assume now for three
thresholds they should be combined in sequence 0.01->0.005->0.002 to give
the final morphing of 0.002. Please correct me if I'm wrong.

Thank you.
Dorian

2013/3/13 susumu mori <susumu at mri.jhu.edu>

> Dorian,
>
> I assume that you are talking about the alpha value you specified when you
> submitted LDDMM and you used 0.005 and 0.004.
>
> If you put two numbers (you can put up to three numbers), we do two
> CONSECUTIVE LDDMM; first using alpha=0.005 and then alpha=0.004. The
> smaller the number the more elastic.
>
> In this case, because most of the image matching is already accomplished
> by the first LDDMM using 0.005, the second LDDMM with 0.004 did very small
> amount of transformation, improving local mismatch.
>
> To see the results with 0.004, you first have to combine two
> transformation matrices, 0.005 and 0.004, and then do a single
> transformation. If you add 0.005 and 0.004 transformation matrices, you get
> the same matrix as the "overall" transformation matrix you also got.
>
> So, you rarely use the 0.004 matrix alone.
>
> If you submit LDDMM twice independently; one with 0.005 and the other with
> 0.004, then you can compare two results with different elasticity values,
> although 0.005 and 0.004 are two close to see large differences.
>
> For young adult brains without atrophy, you can use 0.005. When atrophy is
> severe, we recommend three alpha values with 0.01/0.005/0.002.
>
>
> On Wed, Mar 13, 2013 at 4:28 PM, Dorian P. <alb.net at gmail.com> wrote:
>
>> Hi all,
>>
>> I sent this question yesterday, not sure if it went through because of
>> the attachment.
>>
>> I did a single channel LDDMM on a subject with two thresholds: 0.005 and
>> 0.004. Suprisingly, the lower threshold (0.004) doesn't change much the
>> brain of the subject, preserving the callosum shape. The other threshold
>> (0.005) has worked better on reshaping the subjects callosum to the
>> template shape. This is counterintuitive to say the least, because one
>> would expect to have more morphing at 0.004 than with 0.005.
>>
>> Anybody knows why?
>>
>> Thank you
>>
>> Dorian
>>
>> P.s. Picture is here: http://tinypic.com/r/21ogmf/6
>>
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>
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