[Insight-users] A quick question on combining displacement fields

[Anja Ende]

Hi Brian,

Well, I am open to using any package. However, I also want to make
sure I understand what is happening underneath. hence, the question :)

Cheers,
Anja

On 5 September 2010 02:50, brian avants <stnava at gmail.com> wrote:
> Anja
>
> It sounds to me like you are reproducing features available in ants.  And
> which we will introduce to i tk in the following months.
>
> I suggest looking at ants for your solution. it is i tk compatible.
>
> B
>
> On Sep 4, 2010 4:31 PM, "Anja Ende" <anja.ende at googlemail.com> wrote:
>> Hello,
>>
>> This is a follow up to my earlier question. I have been thinking about
>> this and was wondering if someone could verify whether my line of
>> thinking is correct or now.
>>
>> So, I have these three images A, B and C and I have the following
>> transformations and the displacement fields.
>>
>> - Displacement field in the grid of B (fixed image) that maps each
>> point in image B to a point in image A. This is the result of
>> registering image A (moving image) to image B (fixed image). Let us
>> call this T1.
>>
>> - Displacement field in the grid of C (fixed image) that maps each
>> point in image C to a point in image B. This is the result of
>> registering image B (moving image) to image C (fixed image). Let us
>> call this T2.
>>
>> Now I want to to generate the displacement field that will map each
>> point in image C to each point in image A or equivalantly the result
>> of registering image A (moving image) to image C (fixed image). Can I
>> do the following:
>>
>> - For each index (in mm) in image C, add the corresponding
>> displacement vector from T2 to get the corresponding position in image
>> B.
>> - Transform this position (in mm) in image B to the corresponding
>> voxel position in image B.
>> - Go to that voxel and get the displacement vector from T1 and add it
>> to the calculated physical (mm) position to get to the physical
>> position in image A.
>> - Compute the index position in image A from this physical position.
>>
>> - Resample to compute the corresponding intensity value in the grid
>> position of image C.
>>
>> Does that make sense or is it completely wrong. Is there a better way
>> to go about this?
>>
>> I am sorry this is not a core ITK question but I want to make sure
>> that I understand what I am doing and not blindly use a filter without
>> knowing what it actually does.
>>
>> Many thanks,
>> Anja
>>
>> On 4 September 2010 14:17, Anja Ende <anja.ende at googlemail.com> wrote:
>>> Hello,
>>>
>>> I have a set of three images (say A, B and C) and my registration
>>> process is as follows:
>>>
>>> A (moving image) is registered to B (fixed image) rigidly. I take the
>>> transformation and generate a displacement or position field using the
>>> grid of the fixed image (B).
>>>
>>> B (moving image) is registered to C (fixed image) using non-rigid
>>> transformation. I can generate a similar displacement or position
>>> field using the grid of fixed image (C).
>>>
>>> Now, what I want to do is combine these two displacement or position
>>> fields and generate a composite field that I can use to resample A
>>> using the composite transformation in the space of C.
>>>
>>> However, I am not clear on how I should combine these displacement or
>>> position fields as the grid sizes of B and C may not be the same.
>>>
>>> One simple solution is to do two resampling: first one to resample A
>>> into the space of B and then resample the result using the second
>>> transformation into the space of C. However, I would like to avoid
>>> this multiple resampling, if possible.
>>>
>>> Does anyone have any idea on how I can go about this?
>>>
>>> I would really appreciate your help and comments.
>>>
>>> Thanks,
>>>
>>> Anja
>>>
>>
>>
>>
>> --
>> Cheers,
>>
>> Anja
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-- 
Cheers,

Anja