[Insight-users] question about distance map

[OnezerO]

Thanks for the recomendations maded, i'm going to meditating about all the
process a bit longer.

How i can get more details about the parameters of the geodesic filter,
because the manual for me is a little confuse, like the RMS error
iterations, propagation, etc.

Any help please.

bye 

-----Mensaje original-----
De: Zachary Pincus [mailto:zpincus at stanford.edu] 
Enviado el: Miercoles, 19 de Octubre de 2005 16:40
Para: insight-users @ itk. org
CC: OnezerO
Asunto: Re: [Insight-users] question about distance map

Hello -

First off, make sure to cc the ITK list so that others might also be able to
help you.

Second, note that technically you don't need to provide a full "level set"
image to the algorithm to start. While the signed distance map of the
thresholded input is good, you could technically just pass the thresholded
input (provided the "inside value" is less than the "outside value") as the
initial level set, and set the "level set value" member variable to the
number halfway between the inside and outside values. (If this doesn't make
sense, it is worth meditating on, and if still not, asking for more
details.)

Nevertheless, the fact remains that you think there's a problem with the
initial level set, which is to say a problem with the initial conditions you
are passing to the geodesic active contour level sets algorithm. Without
getting two far into the details, it's important to provide good initial
conditions for the geodesic active contours level sets method: while the
initial level set needn't be completely inside the object to be segmented,
it needs to be close enough to get "sucked in" to the image edges via the
advection term. If you can't generate such an initial segmentation, consider
(a) generating an initial level set completely outside of the bone, and
setting the "reverse propagation direction" (or whatever; consult the
doxygen) flag, or (b) more advanced methods (such as providing your own
speed image that is negative outside of the bone, causing level sets in
outside regions to "shrink" back to the bone area).

I'm not sure what you mean when you say that "it works better"  
without the signed distance map. What, precisely, are you providing as the
initial level set in that case?

Of course, the input is but one of many parameters that can be tuned to make
the geodesic level sets algorithm work better: there's the parameters of the
class itself, plus all of the parameters of the preprocessing steps. I
suggest that you look at each of the output images of these steps to ensure
that the features that are meaningful to your needs are the ones getting
hilighted by the preprocessing.  
Otherwise it's all a waste of time.

Zach

On Oct 19, 2005, at 2:07 PM, OnezerO wrote:

> Hi,
> Thanks for the interest.
> I'm gonna try to explain (my english is kind of bad).
> I want to create a 3D model of a bone structure that's inside of a 
> serial of CT images. For this i'm using the geodesic active contour 
> filter, in the guide of itk said that it's need 2 inputs images, one 
> corresponding to the distance map of the image and another 
> preprocessed image, in this context i dont understand the use of the 
> fastmarching filter, but like the manual said thas use of this filter 
> is to obtain a distance map i think to use danielsson filter.
>
> The process is the next
>
> InputImage -> CurvatureAnisotropicDiffusionImageFilter -> 
> GradientMagnitudeRecursiveGaussianImageFilter -> SigmoidImageFilter -> 
> PotentialEdgeImage
>
> InputImage ->
> ThresholdImageFilter->SignedDanielssonDistanceMapImageFilter-
> >DistanceMapIma
> ge
>
> PotentialEdgeImage-
>              |--> GeodesicActiveContourLevelSetImageFilter -> 
> BinaryThresholdImageFilter -> VTKImageExport ->3D View
>   DistanceMapImage-
>
> When i write the result are bad i mean that the segmentation obtained 
> at the end does't work, i don't obtain the 3d view, if i remove the 
> danielsson filter i get a sementation and hence a 3d image, but this 
> segmentation is not optimal.
>
> I hope now i explain better what my problem is
>
> Thanks
>
> -----Mensaje original-----
> De: Zachary Pincus [mailto:zpincus at stanford.edu] Enviado el: 
> Miercoles, 19 de Octubre de 2005 15:44
> Para: OnezerO
> CC: insight-users at itk.org
> Asunto: Re: [Insight-users] question about distance map
>
> Could you clarify a bit about what you need the distance map for?
> Even better would be to back up and explain what your desired outputs 
> are, what your input images are, what your approach has been, and 
> where you are seeing problems.
>
> When you say "the results are not good" what results do you refer to?
> The Danielsson filter produces good distance maps, so presumably the 
> problem is what you're doing afterward with that distance map.
>
> If you explain your problem and goals a little more, hopefully I or 
> someone else can help.
>
> Zach Pincus
>
> Program in Biomedical Informatics and Department of Biochemistry 
> Stanford University School of Medicine
>
>
> On Oct 19, 2005, at 12:59 PM, OnezerO wrote:
>
>
>>
>>
>>
>> Hello
>>
>> How can i get a distance map without using FastMarching, because i 
>> dont get the method itself, i'm trying to use Danielsson Filter as 
>> well but the results are not good, all the above in the context that 
>> i'm trying to do a example of geodesic active contour to make a 3D 
>> view of any bone. Or is there another method to extract in a better 
>> way the bone inside de images?.
>>
>>  sorry for the english.
>>
>> Thanks
>>
>> _______________________________________________
>> Insight-users mailing list
>> Insight-users at itk.org
>> http://www.itk.org/mailman/listinfo/insight-users
>>
>>
>
>