[Mristudio-users] Counterintuitive LDDMM results

[susumu mori]

that's correct, but if you combine the three, you get the overall Kimap,
which you already have. So it makes sense if you use Ki001 or Ki001+Ki005,
but Ki001+Ki005+Ki002 is the same as Kimap.

On Thu, Mar 14, 2013 at 10:18 AM, Dorian P. <alb.net at gmail.com> wrote:

> 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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>
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