Limited Dataset (dates shifted)

Create a limited dataset with dates retained for longitudinal analysis.

Problem

You’re preparing a limited data set for a research collaborator. Under HIPAA, a limited data set may keep dates and some geographic detail (city, state, ZIP code) but must still remove the direct identifiers such as names and record numbers. You also want to shift the dates by one offset, so the intervals between studies are kept while the real calendar dates are not disclosed.

dcmage has no dedicated Limited Data Set profile. You build one from a profile plus a date shift, and you remain responsible for checking the result against your data use agreement.

Steps

Method A: fixed offset

1. Open your file (⌘O) and switch to Anon mode (Anon in the top bar, ⌘3 in the Mac app, ⌘⇧A in the browser).
2. Choose the profile that removes the identifiers your agreement requires.
3. In Date shift (preserve intervals), type the number of days, for example 10.
4. Click Apply.
5. Filter the tag tree for Study Date. A 10-day shift turns 20051130 into 20051210.

Method B: per-patient offset with Auto

1. Open your file and switch to Anon mode.
2. Click Auto before applying anything else. dcmage derives the offset from the Patient ID, keyed by a secret stored on this installation.
3. Click Apply.
4. Open another study of the same patient on the same installation, click Auto, and check that the offset is the same.

Result

Study Date and every other full date move by the same offset, in YYYYMMDD format, so the intervals between dates are kept. Auto repeats the offset for the same Patient ID on the same installation. Partial or invalid dates are left unchanged by the shift; the tag editor flags malformed dates when you edit them.

The details, limits and a checklist for testing the shift are in DICOM date shifting.