[Insight-users] Speed of Mutual Information calculation

[Luis Ibanez]

Hi Markus,

Nope, this is not the common time for this size of images.

This type of registration should take about 2 minutes in
a modern standard computer.


Some questions:


1) Are you compiling your application for "Release" ?

2) Are you using multi-resolution ?

3) Are you using the GradientDescent or
    the RegularGradientDescent optimizer ?

4) Are you plotting the progress of the optimizer ?
    from a connected Command Observer ?

5) Which one of the 5 ITK implementations of
    Mutual Information Metric  are you using  ?



It is very likely that you are letting the optimizer run
for a lot of uncessary iterations.

Have you measure the time needed for performing One iteration ?
This will indicate if the problem is to have too many iterations,
or to have metric evaluations that are too slow.



The best way to figure out the problem is to analyze the
trace provided by the Command Observer.

Given that you are testing with a 3D translation transform,
you are in the lucky situation were you can actually plot
the path of the optimizer in the parametric space.

You could use a tool such as GNUplot, in order to see this
path in 3D.  Other easy options are a VTK script, or saving
the trace in a .vtk file and loading it into ParaView.

Whi




=====================
Markus Weigert wrote:
> Dear insight users,
>  
> I currently try to register two 3D images (CT and MR)
> by using mutual information as metric.
> The images have a size of approx. 255 * 290 * 75 slices each (MR perhaps 
> even more).
> Although I use a very simple transformation (translation) and a graddescent
> optimizer, one iteration of the optimizer takes more than 1.5h.
>  
> Is this a common time for images of this size???
> The metric uses 60000 spatial samples.
> I thougt about using BSpline transform in the next step of the registration
> with MI metric too, but I think I can forget to do this, if I have to 
> deal with 3000 Parameters
> to be optimized!
>  
> Regards,
> Markus
>  
> 
> 
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