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feat: Add RandNonCentralChiNoise transform

Open karllandheer opened this issue 2 months ago • 1 comments

Adds RandNonCentralChiNoise and RandNonCentralChiNoised, which generalize Rician noise to k degrees of freedom. Standard brain MRI typically uses 32 (or more) quadrature coils, so accurate noise simulation requires this modification, especially in the low SNR limit.

Includes array, dictionary, and test files.

Fixes # .

Description

A few sentences describing the changes proposed in this pull request.

Types of changes

  • [x] Non-breaking change (fix or new feature that would not break existing functionality).
  • [ ] Breaking change (fix or new feature that would cause existing functionality to change).
  • [x] New tests added to cover the changes.
  • [ ] Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
  • [x] Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
  • [x] In-line docstrings updated.
  • [ ] Documentation updated, tested make html command in the docs/ folder.

karllandheer avatar Nov 02 '25 16:11 karllandheer

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Walkthrough

This PR adds a new array RandomizableTransform RandNonCentralChiNoise and a dictionary wrapper RandNonCentralChiNoised (aliases RandNonCentralChiNoiseD / RandNonCentralChiNoiseDict); updates monai/transforms/init.py and CHANGELOG.md to export the new symbols; adds unit tests for both array and dict variants; and appends monai-dev/ to .gitignore. The array transform implements non-central chi sampling with degrees_of_freedom validation, channel-wise and global modes, relative/sample_std options, and dtype handling. The dict wrapper preserves MapTransform semantics and forwards RNG state.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Areas needing attention:

  • monai/transforms/intensity/array.py: non-central-chi sampling logic, root-sum-square aggregation, DoF validation, channel-wise vs global branching, relative/sample_std semantics, and dtype casting.
  • monai/transforms/intensity/dictionary.py: RNG propagation to inner transform, MapTransform key handling, allow_missing_keys behavior, and alias assignments.
  • tests/transforms/*: seeded determinism and analytic expected-value reconstruction for DoF=64 and DoF=2.
  • monai/transforms/init.py and CHANGELOG.md: exported names and changelog entries.
  • .gitignore: new monai-dev/ entry.

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)
Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 41.67% which is insufficient. The required threshold is 80.00%. You can run @coderabbitai generate docstrings to improve docstring coverage.
✅ Passed checks (2 passed)
Check name Status Explanation
Title check ✅ Passed Title directly and clearly summarizes the main change: adding a new RandNonCentralChiNoise transform, matching the primary objective.
Description check ✅ Passed Description covers the purpose (generalizing Rician noise), includes context (MRI coils), checks the main template checkboxes (non-breaking change, tests added, quick tests passed, docstrings updated), and lists included file categories.
✨ Finishing touches
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  • [ ] Post copyable unit tests in a comment
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📥 Commits

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  • monai/transforms/__init__.py (2 hunks)
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**/*.py

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🔇 Additional comments (2)
monai/transforms/__init__.py (2)

120-120: LGTM!

Alphabetically ordered and follows naming convention.

203-205: LGTM!

All three dictionary aliases present, alphabetically ordered, consistent with existing patterns.

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