FAQ

Frequently Asked Questions about PhysioMotion4D.

General Questions

What is PhysioMotion4D?

PhysioMotion4D is a medical imaging package that converts 4D CT scans into dynamic 3D models for visualization in NVIDIA Omniverse.

What data formats are supported?

Input: NRRD, MHA, NIfTI, DICOM
Output: USD (Universal Scene Description), VTK

Do I need NVIDIA Omniverse?

No, Omniverse is optional for visualization. You can also use:

usdview (comes with usd-core)
PyVista
ParaView

Installation Questions

Do I need a GPU?

No. A plain pip install physiomotion4d works without a GPU. At import time a UserWarning is emitted (visible by default in all standard Python runs):

CuPy is not installed — GPU acceleration is unavailable and processing will be
slow. Re-install with uv to get CuPy and CUDA-enabled PyTorch in one step
(pip alone will not select the correct CUDA wheel):
  uv pip install 'physiomotion4d[cuda13]'  # CUDA 13

CPU-only mode is suitable for evaluation and small datasets. For production workloads an NVIDIA GPU is strongly recommended.

Which CUDA version is required?

CUDA 13 is supported. Install the CUDA 13 extra for GPU acceleration:

uv pip install "physiomotion4d[cuda13]"

The extra installs CuPy. In uv-managed source environments, PyTorch, torchvision, and torchaudio are sourced from https://download.pytorch.org/whl/cu130 by default.

What Python version is required?

Python 3.11 or 3.12 are supported.

Usage Questions

How long does processing take?

Typical processing time for 10-frame cardiac CT (with GPU):

4D to 3D conversion: ~1 minute
Registration: ~5-10 minutes
Segmentation: ~1-2 minutes
USD creation: ~1 minute
Total: ~10-15 minutes

Which segmentation method should I use?

TotalSegmentator: Fast, good quality, general purpose
Simpleware: Best quality for cardiac imaging, requires Simpleware Medical

See Segmentation Modules for comparison.

Which registration method should I use?

ICON: Recommended for cardiac/lung (fast, GPU)
ANTs: Best for brain imaging and general purpose

See Image Registration Modules for comparison.

Troubleshooting

See Troubleshooting for common issues and solutions.