ActiveMedAgent: Cost-Aware Trajectory Learning for Multimodal Medical Diagnosis

Weiwei Ma, Xiaobing Yu, Peijie Qiu, Jin Yang, Zhaoqi An, Xuanzhao Dong, Xiaoqi Zhao, Xiaofeng Liu


Abstract
Clinical diagnosis is inherently sequential: clinicians escalate from cheap to costly tests only when additional evidence is expected to resolve diagnostic uncertainty. We present ActiveMedAgent, a framework that brings this cost-aware sequential logic to multimodal medical AI. Given a frozen, API-accessed vision-language model, ActiveMedAgent probability distributions over candidate diagnoses induced each acquisition by its per-step diagnostic utility minus cost. A lightweight MLP controller is then trained offline on these scored trajectories, learning when to request additional evidence and when to commit. Across three commonly used benchmarks, trajectory-based policy learning consistently outperforms both unguided acquisition and full-modality baselines. Notably, we identify an information overload effect. In 175 cases, the agent produces a correct diagnosis with fewer channels while the full-modality baseline fails, showing that learning what to omit can be as important as learning what to acquire
Anthology ID:
2026.findings-emnlp.1434
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
30576–30595
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1434/
DOI:
Bibkey:
Cite (ACL):
Weiwei Ma, Xiaobing Yu, Peijie Qiu, Jin Yang, Zhaoqi An, Xuanzhao Dong, Xiaoqi Zhao, and Xiaofeng Liu. 2026. ActiveMedAgent: Cost-Aware Trajectory Learning for Multimodal Medical Diagnosis. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 30576–30595, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
ActiveMedAgent: Cost-Aware Trajectory Learning for Multimodal Medical Diagnosis (Ma et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1434.pdf