fullseye

metal_trace_interpolate — TOMOGRAPHY artifact op

使い方

Linear-interpolation metal artefact reduction (LI-MAR).

A metal implant attenuates so strongly that its detector bins carry almost no photons; the measured line integrals there are dominated by scatter and by the noise floor of the logarithm, and back-projecting them lays down the dark bands and bright streaks between dense objects that make a slice unreadable.

The oldest working answer, and still the baseline every newer method is compared against: declare the affected bins missing and fill them by linear interpolation along the detector axis, per angle. The result is not the truth — it is a smooth guess with the streaks removed — and it blurs whatever was genuinely behind the metal.

How the affected bins are found matters more than the interpolation, and the obvious way is measurably worse than doing nothing. The metal trace is located the way LI-MAR actually does it: reconstruct once with :func:filtered_backprojection, threshold the image at mean + 3*std, forward-project that binary mask, and treat the bins it touches as missing. Thresholding the sinogram directly is the shortcut that suggests itself, and on the Shepp-Logan phantom with a 6-px implant it goes wrong in the direction that is hardest to notice — it flags the densest legitimate structure (the skull, seen edge-on) and interpolates it away:

implant density   uncorrected   sinogram threshold   image threshold
     x8             0.0487           0.0626              0.0255
    x30             0.1583           0.2249              0.0255
   x100             0.5214           0.7127              0.0257

(normalised RMS error against the metal-free truth, outside the implant footprint; the metal-free reconstruction itself scores 0.0250.) The image route recovers essentially all of the damage at every density. The sinogram route makes it 1.3-1.4x worse than not correcting at all, at every density, while still producing a picture with fewer visible streaks — which is why the shortcut is not offered as an option here rather than merely discouraged.

Inside the implant footprint the reconstruction is now wrong on purpose: the metal is gone. Clinical practice puts it back from the thresholded reconstruction afterwards; that step is not implemented.

:param sinogram: (n_angles, n_detectors). :param angles_deg: view angles; None -> uniform [0, 180). Used for the internal reconstruction and re-projection, so a wrong angle set here misplaces the trace. :param image_threshold: image-domain metal threshold; None -> mean + 3*std of the internal reconstruction. :param mask: explicit boolean (n_angles, n_detectors) metal trace. When given, no reconstruction is done and image_threshold is ignored — this is the route to use when the trace comes from a segmentation you trust. :param size: side of the internal reconstruction; None -> the inscribed square. :returns: (n_angles, n_detectors) float64 sinogram. :raises ValueError: if the mask shape disagrees with the sinogram, if the mask is not boolean, if nothing is left to interpolate from, or if any row is entirely masked.

参考(サンプルデータ・文献)

実行できる例(この op を実際に呼ぶ検証済みサンプル)

型が繋がる次の op(sinogram を入力に取れる)

backproject_sinogram · filtered_backprojection · sart_reconstruct · beam_hardening_apply · beam_hardening_correct · ring_artifact_apply · ring_artifact_remove · sinogram_center_of_rotation

同カテゴリ(artifact)

beam_hardening_apply · beam_hardening_correct · ring_artifact_apply · ring_artifact_remove

Provenance: tomography.py — TOMOGRAPHY operator registry. この per-op ノートは tools/opdocs.py md が自動生成(手編集しない)。

© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.

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