[Insight-users] Registration - Mutual Information Metric - Sampling from Moving Image

[Sharath Venkatesha]

Hi Luis,


I am already using the 

 registration->SetFixedImageRegion( region ) 

My scaling parameters are around 0.6 and rotation of 6-7 degrees, I have to use a big region  in the fixed image (I am initialiazing with scale =0.5, and hence using a region of size 1280*960).  The performance has not improved much. 

Hence I want to sample pixels from the moving image, and do a backward mapping to pixels in the fixed image( by the inverse transform parameters, that are estimated in each iteration of the optimizer). In this case, I think that almost all the points will be mapped, and hence the metric will be better. Also, it will take care of the scale and translation, as in the previous case, a wrong initial scale will make me miss out the the pixel values in the fixed image.


Do I need to change the functions in the respective files, or is there a simpler way to do this, or is already implemented?

Thanks,

Sharath Venkatesha



________________________________
From: Luis Ibanez <luis.ibanez at kitware.com>
To: Sharath Venkatesha <sharath20284 at yahoo.com>
Cc: Insight users <insight-users at itk.org>
Sent: Saturday, July 11, 2009 8:49:51 AM
Subject: Re: [Insight-users] Registration - Mutual Information Metric -  Sampling from Moving Image


Hi Sharath,

You are right in that it is not a good idea to take samples
from the entire 2000 x 2000 pixels image if we expect that
only a regions of 640 x 480 is going to match the Moving
image.

The solution is to simply call 

            registration->SetFixedImageRegion( region )

 and set "region" to the region of interest from the 
2000 x 2000 image, where you anticipate to find matches
for the moving image.


You will find examples on the use of 

       SetFixedImageRegion()

in the ITK software Guide

       http://www.itk.org/ItkSoftwareGuide.pdf

and most (if not all) the corresponding Image Registration
examples in 

            Insight/Examples/Registration




   Regards,


         Luis



---------------------------------------------------------------

On Fri, Jul 10, 2009 at 9:15 PM, Sharath Venkatesha <sharath20284 at yahoo.com> wrote:


>>Hi,
>
>>I am working with images where the Fixed image is 2000*2000 pixels and the moving image is 640*480 (sub region of the fixed image). In all the Mutual Information metrics, the sampling is done on the Fixed image, and the transformed points are mapped on the moving image.
>
>>I figured out that it is incorrect to sample the points randomly in the full fixed image ( as in my case, the moving image is a sub-part of the fixed image, and only 30-40% points were mapped), I used an approximate region of the fixed image from which sampling should be done. This has not improved the performance/accuracy of registration.
>
>>I am thinking of sampling pixels from the moving image, and do a backward mapping to pixels in the fixed image. In this case, I think that almost all the points will be mapped, and hence the metric will be better.
>
>>Do I need to change the functions in the respective files, or is there a simpler way to do this, or is already implemented?
>
>>Thanks,
>
>>Sharath Venkatesha
>
>
>
>
>
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