How to specify "stiffness" of images?

[dzenanz]

I am hoping to be able to specify that part of the image closer to ultrasound transducer should deform less than parts further away.

• BSplineTransformWithDiffusion mentions "stiffness coefficient image", but does not explain how to provide it. Is BSplineTransformWithDiffusion even good for this purpose?

• Can TransformRigidityPenalty accomplish this? Can I get away with computing/using just one of the 3 terms? Which one? In ITKElastix, can RigidityImages be passed through memory, without having to write them to disk?

Also, ideally, the voxels next to the transducer should not move perpendicularly to it, but would be allowed to slide sideways.

• I am thinking that this part could be accomplished by artificially expanding the image "into the transducer" and filling it with all "white" pixels, which would create a strong signal to the registration and mitigate/prevent perpendicular movement.
• Would "DistancePreservingRigidityPenalty" help with this?

Any further thoughts?

[dzenanz]

Some answer to my own question. I tried TransformRigidityPenalty approach, by constructing a low-resolution image with high stiffness near transducer face. This makes the registration about twice slower, as most of the metric computation time at higher resolutions is spent on computing that metric. More importantly, it made a barely noticeable change. I have given up on this.

I will try artificially expanding the image "into the transducer" and filling it with all "white" pixels, which would create a strong signal to the registration and mitigate/prevent perpendicular movement.