dcmage DOCS APP
Anonymization

Consistent patient ID across studies

Maintain consistent pseudonyms for the same patient across multiple studies.

Problem

You’re de-identifying multiple DICOM studies from the same patient for a multi-site research dataset. You need to replace the original Study Instance UIDs (which are globally unique and traceable) with pseudonyms, but you must ensure that the same original UID always maps to the same pseudonym across all studies. Without this consistency, a single patient’s studies cannot be linked together in the de-identified dataset — breaking longitudinal analysis.

Additionally, distinct source UIDs must never collide (map to the same pseudonym). If Study UID A and Series UID B both mapped to 2.25.123, the dataset would have corrupted referential integrity.

Steps

  1. Open your DICOM file (⌘O) and switch to Edit mode (⌘3).

  2. Note the original Study Instance UID — filter for (0020,000D) and record the current value.

  3. Switch to Anon mode (⌘2), select the Basic profile, and click Apply.

  4. Verify the remapped UID — switch back to Edit mode and check (0020,000D). The UID should:

    • Start with 2.25. (the OID root used for derived UIDs)
    • Be different from the original UID
    • Match the deterministic SHA-256 hash of the original (same input → same output)

  5. Verify distinct inputs stay distinct — filter for both (0020,000D) (Study UID) and (0020,000E) (Series UID). These must be different original values, and after anonymization, their pseudonyms must also be different.

Expected Result

  • Study Instance UID (0020,000D) is replaced with a 2.25.* pseudonym.
  • The pseudonym is computed as: 2.25. + first 128 bits of SHA-256(original UID) expressed as a decimal integer.
  • The same original UID always produces the same pseudonym — rebuild the dataset six months later and the mapping is identical.
  • Two different source UIDs (e.g. Study UID vs Series UID) produce two different pseudonyms — no collision.
  • The remap is consistent across studies: if Study A and Study B originally shared the same Study Instance UID, they continue to share the same pseudonym after de-identification.
  • Series Instance UIDs and SOP Instance UIDs are similarly remapped using the same deterministic formula, preserving internal referential integrity.
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