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# Does different image parameters affect image registration?

Asked by Colleen on 3 Oct 2013
Latest activity Commented on by Alex Taylor on 8 Oct 2013

I am currently trying to register 2, 3D CT images of a human tibia. I have implemented imregister to complete this task. When I register the right to left leg of the same individual from the same day, the registration is excellent. However, when I register the left leg to the left leg of the same individual 3 years later the registration is very poor. The CT collected a slice every 0.4mm but I noticed that the image spacing was different in the other 2 planes. One CT scan had image spacing of 0.156 x 0.156 x 0.4 while the other was 0.195 x 0.195 x 0.4. Could this explain the poor registration? Is there a way to specific the image spacing to improve the registration? Please let me know if my question is unclear or if you need more information/code/images. Thank you.

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Answer by Alex Taylor on 4 Oct 2013
Edited by Alex Taylor on 4 Oct 2013

Hi Colleen, I would recommend you take a look at the following example that ships with the Image Processing Toolbox:

http://www.mathworks.com/help/images/examples/registering-multimodal-3-d-medical-images.html

It shows how spatial referencing objects can be used to specify the resolution of your images in each dimension and improve 3-D registration results with imregister.

In your case, the first CT image you described would have a spatial referencing object defined as:

` Rct = imref3d(size(yourImage), 0.156,  0.156, 0.4);`

Where yourImage is the variable that contains the first CT image.

Passing spatial referencing information can be very useful in getting imregister/imregtform to converge.

Colleen on 6 Oct 2013

Hi Alex, this worked very well and solved my problem! Now, the registration is very good. Thanks for all your help and the suggested example. It was very helpful.

Alex Taylor on 8 Oct 2013

Collen,

I'm happy to hear that! Thanks for letting me know it worked out.

Answer by Ashish Uthama on 3 Oct 2013

Difference in spatial resolution differece might explain the poor registration.

You could specify the image spacing using using imref3d and use it with imregister.