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fix: warn when PydicomReader cannot determine affine from DICOM metadata (Fixes #8468) #8922

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fix: warn when PydicomReader cannot determine affine from DICOM metadata (Fixes #8468) #8922

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05aa9f2
fix: warn when PydicomReader cannot determine affine from DICOM metadata
rtmalikian Jun 18, 2026
78ac03b
docs: add Warns section to _get_affine docstring documenting the miss…
rtmalikian Jun 18, 2026
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13 changes: 13 additions & 0 deletions monai/data/image_reader.py
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Original file line number Diff line number Diff line change
Expand Up @@ -735,9 +735,22 @@ def _get_affine(self, metadata: dict, lps_to_ras: bool = True):
metadata: metadata with dict type.
lps_to_ras: whether to convert the affine matrix from "LPS" to "RAS". Defaults to True.

Warns:
UserWarning: when ImageOrientationPatient (00200037) or ImagePositionPatient
(00200032) is missing from metadata. The affine matrix is set to identity,
which may be incorrect. Common with multiframe DICOM files.

"""
affine: np.ndarray = np.eye(4)
if not ("00200037" in metadata and "00200032" in metadata):
warnings.warn(
"PydicomReader: ImageOrientationPatient (00200037) or "
"ImagePositionPatient (00200032) not found in DICOM metadata. "
"The affine matrix will be set to identity, which may be incorrect. "
"This commonly occurs with multiframe DICOM files (e.g., Enhanced CT). "
"Consider using ITKReader for accurate spatial metadata.",
stacklevel=2,
)
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return affine
# "00200037" is the tag of `ImageOrientationPatient`
rx, ry, rz, cx, cy, cz = metadata["00200037"]["Value"]
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