Objectives To estimate an upper bound of memory-based re-identification risk for chest radiographs by testing radiologists under conditions that favor recognition. Materials and methods In this prospective, multicenter, web-based reader study, radiologists from 38 centers completed two reading phases. In Phase 1, each reader interpreted ten chest radiographs. After a minimum interval of 24 h, Phase 2 included six follow-up target examinations and six new non-target examinations (50% target prevalence). After each Phase-2 examination, readers indicated whether they remembered the patient. Following a positive response, they were asked separately whether they remembered the Phase-1 pseudonym and/or case position. Thirty-three readers with fully classifiable Phase-2 data contributed 396 Phase-2 examinations to the predefined primary analysis. Results Readers answered “remember” in 139 of 396 examinations (35.1%). Sensitivity for repeated target examinations was 50.0% (99/198), whereas 20.2% of new non-target examinations were nevertheless judged as remembered (40/198). Explicit identifiers were attempted in 23 of 396 examinations (5.8%). At least one explicit identifier, defined as the Phase-1 pseudonym and/or case position, was correct in five of 396 examinations (1.3%). In a low-prevalence model with one known patient per dataset, the positive predictive value of a “remember” response decreased from 2.44% in datasets of 100 radiographs to 0.25% in datasets of 1000 radiographs. Conclusions Even in a design that favored memory, correct recall of explicit identifiers was rare, whereas false-positive recognition remained common. These findings support treating radiologists’ memory as a limited, upper-bound component of re-identification risk, rather than assuming that familiarity routinely translates into identification. Critical relevance statement Even under conditions deliberately favoring memory, radiologists rarely converted familiarity with prior chest radiographs into correct explicit identifiers; in low-prevalence datasets, false-positive recognition dominated the practical meaning of a “remember” judgment. Key Points <UnorderedList Mark="Bullet"> <ItemContent> How often does a radiologist’s feeling of familiarity with a previously seen chest radiograph translate into correct recall of a usable explicit identifier? </ItemContent> <ItemContent> In a deliberately memory-favoring design, sensitivity was 50.0%, but 20.2% of new examinations were false positives and only 1.3% yielded a correct explicit identifier. </ItemContent> </UnorderedList> Graphical Abstract

Radiologists’ memory as a data protection risk: a worst-case stress test for chest radiograph re-identification

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2026年6月16日

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Matthias A. Fink,
Christian Römer,
Matthis Ebel,
Eric Frodl,
Daniel Pinto dos Santos,
Hans-Ulrich Kauczor,
Andreas Bucher

摘要

Objectives

To estimate an upper bound of memory-based re-identification risk for chest radiographs by testing radiologists under conditions that favor recognition.

Materials and methods

In this prospective, multicenter, web-based reader study, radiologists from 38 centers completed two reading phases. In Phase 1, each reader interpreted ten chest radiographs. After a minimum interval of 24 h, Phase 2 included six follow-up target examinations and six new non-target examinations (50% target prevalence). After each Phase-2 examination, readers indicated whether they remembered the patient. Following a positive response, they were asked separately whether they remembered the Phase-1 pseudonym and/or case position. Thirty-three readers with fully classifiable Phase-2 data contributed 396 Phase-2 examinations to the predefined primary analysis.

Results

Readers answered “remember” in 139 of 396 examinations (35.1%). Sensitivity for repeated target examinations was 50.0% (99/198), whereas 20.2% of new non-target examinations were nevertheless judged as remembered (40/198). Explicit identifiers were attempted in 23 of 396 examinations (5.8%). At least one explicit identifier, defined as the Phase-1 pseudonym and/or case position, was correct in five of 396 examinations (1.3%). In a low-prevalence model with one known patient per dataset, the positive predictive value of a “remember” response decreased from 2.44% in datasets of 100 radiographs to 0.25% in datasets of 1000 radiographs.

Conclusions

Even in a design that favored memory, correct recall of explicit identifiers was rare, whereas false-positive recognition remained common. These findings support treating radiologists’ memory as a limited, upper-bound component of re-identification risk, rather than assuming that familiarity routinely translates into identification.

Critical relevance statement

Even under conditions deliberately favoring memory, radiologists rarely converted familiarity with prior chest radiographs into correct explicit identifiers; in low-prevalence datasets, false-positive recognition dominated the practical meaning of a “remember” judgment.

Key Points

How often does a radiologist’s feeling of familiarity with a previously seen chest radiograph translate into correct recall of a usable explicit identifier?

In a deliberately memory-favoring design, sensitivity was 50.0%, but 20.2% of new examinations were false positives and only 1.3% yielded a correct explicit identifier.

Graphical Abstract