Applying a Diffeomorphic Registration Transform to Other Images

You can estimate the deformation that maps an image onto the fixed image, and then apply the same deformation to second image. This might be useful where the second image has much poorer signal-to-noise ratio, or different contrast that makes it difficult to estimate the transform. Application of a previously-found deformation is also much quicker, so this could save considerable time in cases where you know that the deformation is the same for a series of images. Finally, you may want to make sure that the same deformation is applied to a series of images.

Saving the Deformation to Disk

For diffeomorphic registration, the deformation is defined by the pair of vector fields that represent the "flow" of the moving image onto the fixed image. To save the estimated deformation to disk, ensure that the Select to save the deforming vector fields to disk check-box is ticked. When you perform the registration, an additional image will now be created on disk for each image to register: this will have the suffix "_V" appended to the name of the image being registered, and will contain the deforming vector fields for that image.

Applying the Deformation to Another Image

To apply the deformation to another image, ensure that the Select to read the deforming vector fields image from disk check-box is ticked, and select the image that contains the vector fields want to apply:

Selecting the vector fields image for diffeomorphic registration

The same deformation will be applied to all the images to be registered.

Note: it only makes sense to do this if the new image to be registered has the same field-of-view in all directions as the original image which was registered to find the deformations.

If you want to invert the deformation, before you apply it, select Select to invert the registration transform before applying it check-box. You may want to do this if you want to register what was previously the fixed image to what was previously a moving image.

Note: if you invert the deformation, the inversion will not be "exact". Computing the deformation involves numerical integration through the vector fields, and by its nature numerical integration is not exact. The more "integration time steps" you set when performing the original registration, the closer will the approximate inverse deformation be to the true inverse.

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