Add ImpactReg extension

[vboussot]

New extension

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---

This PR adds IMPACT-Reg, a new extension enabling multimodal medical image registration directly inside 3D Slicer.

IMPACT-Reg integrates the IMPACT deep semantic similarity metric into the Elastix registration tools and exposes it through a user-friendly GUI.

---

Key functionality included

• Deep semantic registration (CT–CBCT, MR–CT, etc.)
• GPU-accelerated feature extraction when available
• Sequential execution of multiple presets
• Automatic warped volume and transform generation
• Built-in evaluation tools (landmarks, segmentations)
• Support for uncertainty analysis based on transform ensembles

---

The module depends on the KonfAI extension, which provides KonfAI App execution support.

[lassoan]

Thanks for your contribution! As I see, a custom build of Elastix binaries is downloaded from somewhere, but I could not easily find from where and how. Could you please clarify?

[lassoan]

FYI, on Windows I get this error when I try to run the registration:

Elastix execution failed.

Command:
C:\D\SlicerImpactReg\ImpactReg\Resources\bin\elastix-impact\elastix.exe -h
Return code: 3221225781

[vboussot]

The custom elastix binaries are simply a compilation of elastix with the IMPACT similarity metric enabled.

IMPACT relies on LibTorch at runtime to extract deep features.
As a result, the elastix build depends not only on the operating system, but also on the availability of a GPU driver.

For this reason, multiple pre-built elastix binaries are provided (CPU-only and CUDA-enabled).
When the elastix binaries are not yet installed (typically on the first use of SlicerImpactReg), the install.py script
(https://github.com/vboussot/SlicerImpactReg/blob/main/ImpactReg/Resources/bin/install.py
) is executed.

This script automatically selects the appropriate build, downloads it, and (if needed) fetches the matching LibTorch version and ensures it is correctly linked at runtime, so that elastix works out of the box.

[vboussot]

This return code usually indicates a missing runtime DLL.
Could you please provide the dependency listing for elastix.exe, for example using:

dumpbin /DEPENDENTS elastix.exe

This should help identify which runtime dependency is missing.

[lassoan]

On Windows (with Slicer-5.10), the custom-built Elastix packages are not self-contained - several pytorch DLLs are missing (even from the CPU package, such as fbgemm.dll). They work if I copy (and overwrite all existing DLLs) from "...\AppData\Local\slicer.org\3D Slicer 5.10.0\lib\Python\Lib\site-packages\torch\lib" to elastix-impact folder. Of course, the clean solution would be not to include torch binaries in the custom Elastix packages (not even for the CPU version, as it is incomplete anyway) and set the path before launching Elastix to make the loader find the torch DLLs (instead of copying them over).

FYI, on an RTX3060, registering MRBrainTumor1 to MRBrainTumor1 is really slow (it is at 35% after about 30 minutes). This is a problem, because Elastix basic bpsline takes <1min on CPU and it usually gives acceptable results.

[lassoan]

When I attempt to run elastix.exe from elastix-impact-windows-x86_64-shared-with-deps-cpu.zip, I get errors about missing fbgemm.dll and libiomp5md.dll.