Add radial high-pass emphasis distortion for k-space sharpening

[Copilot]

This adds a sharpening-style k-space distortion that boosts high frequencies radially. The new operator follows the existing self-adjoint multiplicative-mask distortion pattern and uses the shared normalized radial frequency utility.

• What changed

  • Added RadialHighPassEmphasisDistortion in mri_recon.distortions.resolution
  • Implemented the mask as 1 + alpha * r**exponent, where r is the normalized radial frequency
  • Validated parameters to reject negative alpha and non-positive exponent

• Package surface

  • Exported the new distortion from mri_recon.distortions
  • Added it to the example distortion selector for quick use in inference plotting

• Coverage and docs

  • Added focused tests for:
    • inheritance from SelfAdjointMultiplicativeMaskDistortion
    • center vs edge mask values
    • identity behavior when alpha=0
  • Documented the new distortion in the README distortions table

[Copilot]

Pull request overview

This PR introduces a new resolution-related k-space distortion that radially boosts high-frequency content (sharpening-style) via a self-adjoint multiplicative mask, and wires it into the public API, examples, tests, and README documentation.

Changes:

• Added RadialHighPassEmphasisDistortion implementing a radial gain mask 1 + alpha * r**exponent with parameter validation.
• Exported the new distortion from mri_recon.distortions and added it to the example distortion selector for inference plotting.
• Added unit tests covering mask behavior (center vs edge) and identity behavior at alpha=0, plus README table entry.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
mri_recon/distortions/resolution.py	Adds the new radial high-pass emphasis distortion implementation and validation.
mri_recon/distortions/__init__.py	Exposes the new distortion in the package surface exports.
tests/test_distortions.py	Adds selection support and focused tests for the new distortion and updates inheritance coverage list.
examples/fastmri_inference_plot.py	Adds the new distortion to the selectable options and factory.
README.md	Documents the new distortion in the distortions table.

Comments suppressed due to low confidence (1)

tests/test_distortions.py:589

• The docstring says this test covers "resolution-reduction classes", but the parametrized list now includes RadialHighPassEmphasisDistortion (a sharpening/gain mask, not a reduction). Please update the docstring (and possibly the test name) to reflect that it's validating all SelfAdjointMultiplicativeMaskDistortion subclasses in the resolution module (or similar), so the test intent matches the covered classes.

def test_resolution_reduction_classes_inherit_from_self_adjoint_multiplicative_mask(
    distortion_cls,
):
    """Verify that all resolution-reduction classes are subclasses of the shared super class."""
    assert issubclass(distortion_cls, SelfAdjointMultiplicativeMaskDistortion)

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.