"InitialTransformation" appears not to work when used on 3D images

I am attempting image registration of two 3D images and am having issues applying the "InitialTransformation" option of the imregister/imregtform functions to a set of 3D images. I have attached an example, described below.

The Mathworks website includes a nice 2D example in which a rigid registration is used to get an initial transformation, which is fed back into a second affine registration as the "InitialTransformation" - here is the link to the example, go to Step 4. I follow their steps closely, except 1) I have subbed their 2D images out for my 3D images and 2) I am performing an initial "rigid" transformation where they are using a "similarity" transformation instead. The rigid transformation works reasonably well and gets close, but the secondary affine transformation with the "InitialTransformation" in this example is completely wonky. In many of my other attempts (with other images), the secondary transformation simply throws the following warning text nearly immediately, regardless of the actual MaximumStepLength used:

"Warning: Registration failed because optimization diverged. Try reducing the MaximumStepLength property of the optimizer. "

On the other hand, an affine transformation with no "InitialTransformation" specified performs much better, so it seems to be the initial transformation that is causing the issue. I have tried tinkering with the optimizer settings to no avail. I have also tried iterations of this code where I have also supplied the imref3d objects for the fixed and moving images, and that does not seem to help.

Can anyone offer advice on why this might be happening? Am I making a mistake, or do some special considerations need to be taken when using InitialTransformation on 3D images? Is there perhaps some example of this being successfully done in 3D that I have not come across yet? I want to note that I specifically am interested in getting this two-step registration working process, not just getting a nice registration for this example. My code and a TIF showing my results are all attached. I cannot attach my 3D images due to size, but would be happy to share with anyone interested in using them to troubleshoot. Thanks for any help you can provide.

[Andrea Jacobson]

Hello,

I am also trying to work on this issue. Did you ever figure out what the issue was?