MediConfusion: Can you trust your AI radiologist? Probing the reliability of multimodal medical foundation models

Authors: Mohammad Shahab Sepehri, Zalan Fabian, Maryam Soltanolkotabi, Mahdi Soltanolkotabi
Primary area: datasets and benchmarks
Keywords: medical foundation models, benchmarking, vision encoding, radiology

Abstract:
Multimodal Large Language Models (MLLMs) have tremendous potential to improve the accuracy, availability, and cost-effectiveness of healthcare by providing automated solutions or serving as aids to medical professionals. Despite promising first steps in developing medical MLLMs in the past few years, their capabilities and limitations are not well understood. Recently, many benchmark datasets have been proposed that test the general medical knowledge of such models across a variety of medical areas. However, the systematic failure modes and vulnerabilities of such models are severely underexplored with most medical benchmarks failing to expose the shortcomings of existing models in this safety-critical domain. In this paper, we introduce MediConfusion, a challenging medical Visual Question Answering (VQA) benchmark dataset, that probes the failure modes of medical MLLMs from a vision perspective. We reveal that state-of-the-art models are easily confused by image pairs that are otherwise visually dissimilar and clearly distinct for medical experts. Strikingly, all available models (open-source or proprietary) achieve performance below random guessing on MediConfusion, raising serious concerns about the reliability of existing medical MLLMs for healthcare deployment. We also extract common patterns of model failure that may help the design of a new generation of more trustworthy and reliable MLLMs in healthcare.

Decision: accept (poster)
Reviewer scores: 6, 8, 5, 6

Reviews and discussion:
<thread>
creation date:
1730602263185

thread_type:
official_review

<thread_object>
creator: reviewer_772b

<content>
summary:
The paper introduces MediConfusion, a challenging medical Visual Question Answering (VQA) benchmark that exposes the vulnerabilities of current medical multimodal large language models (MLLMs) by highlighting their failure modes. Despite promising progress, existing models—open-source and proprietary—struggle significantly, even performing below random guessing in certain tests. This suggests major reliability issues in deploying these models for healthcare. The benchmark was guided by clinician experts, using adversarial examples to stress-test models, offering a valuable resource for the research community to design more trustworthy MLLMs. Personally I like this paper because it hits on a crucial gap in medical AI that’s often overlooked.

strengths:
1. The paper brings a novel perspective by focusing on the systematic failure modes of medical multimodal models—something that hasn’t been extensively explored before. The fact that state-of-the-art models performed at or below random guessing levels is a striking finding. I can see this dataset becoming a benchmark everyone wants to use as soon as the paper is out, as it offers a strong challenge to prove model reliability.

2. The presentation and writing are clear and well-structured.

weaknesses:
1. One significant limitation is that it feels almost obvious to train a model using both public data and this new dataset to demonstrate improved performance over current models. It’s surprising this wasn’t attempted—even for a dataset paper. Adding such experiments could have strengthened the impact by showing how incorporating MediConfusion directly improves model reliability.

2. The authors might also want to discuss the importance of the image encoder in these models. For example, both LLaVA and LLaVA-med use encoders trained on everyday images, which could be a reason why LLaVA-med performs even worse than LLaVA. If the encoder isn’t well-suited for medical images, it limits the model's ability to learn effectively. Highlighting the role of specialized image encoders could have added valuable insights into improving model reliability in the medical domain.

questions:
See the weakness.
</content>
</thread_object>

</thread>
<thread>
creation date:
1730682420834

thread_type:
official_review

<thread_object>
creator: reviewer_ct2v

<content>
summary:
This paper evaluates the reliability of medical Multimodal Large Language Models in healthcare. The authors present MediConfusion, a new VQA benchmark that highlights distinguishing similar medical xray images. They find that all tested MLLMs, open-source and proprietary, perform below random chance on MediConfusion, indicating serious reliability issues.

strengths:
- The idea of using the same question with similar images could offer a interesting way to probe model weaknesses.

- With the help of an expert-in-the-loop pipeline, the paper thoroughly examines why models struggle to differentiate between visually similar medical images.

- The evaluation metrics are comprehensive, particularly accommodating models unable to directly answer multiple-choice questions.

weaknesses:
- The motivation is not clear. The authors claimed that "existing benchmark datasets are focused on evaluating the medical knowledge of MLLMs across large evaluation sets, heavily biased towards common or typical scenarios." What are the common and typical scenarios? Could you provide a more detailed discussion about this limitation of existing benchmarks and how the proposed benchmark in this paper can overcome the limitations?
- The results show that all available models (open-source or proprietary) achieve performance below random guessing on MediConfusion. It would be better if the authors conducted more experiments to find the reasons. For example, by using different sim_med and sim_gen thresholds and compare the model performance, we can identify whether the models can differentiate easy image pairs or they even cannot differentiate any image pairs. 
- The writing style needs refinement. For instance, the phrase "stress-tests the visual capabilities of state-of-the-art models" is unclear and may confuse readers. The motivation and innovative aspects of the benchmark remain vague until "image pair" is mentioned at the end of Section 2, and even then, it is not clarified that the task is framed as multiple-choice questions. It would be easier for the readers to better understand this paper if the writer could clarify these designs in the introduction section.
- The rationale for focusing on the medical domain is unclear. The methods do not appear specific to this field, resembling a rephrasing of existing VQA datasets where answers are scrambled, and models are tasked with similar image comparisons. Could you explain what is the specific design of this benchmark considering its medical context? What is the difference between two similar medical images and two similar general images?
- The choice to format the task as multiple-choice is questionable. Have you considered open-ended QA or report generation of CXR images? Additionally, given the relatively small dataset (352 questions), this benchmark may lack the scale needed to effectively assess MLLM capabilities. Could you justify that 352 questions are sufficient for the evaluation?

questions:
- Does the proposed benchmark dataset only contain 352 image pairs?

- The authors only evaluate the models on the similar pair images. Can the models work well on different image pairs? For example, to use different sim_med and sim_gen thresholds and compare the model performance.
</content>
</thread_object>

</thread>
<thread>
creation date:
1730699601813

thread_type:
official_review

<thread_object>
creator: reviewer_bwv6

<content>
summary:
This paper evaluates reliability of medical VLMs. The authors introduce MediConfusion, a benchmark comprising 352 pairs of “confusing” medical images. Each pair consists of images that are visually distinct yet similar in feature space. The authors leverage GPT-4 to generate questions for which the answers differ between the two images. The benchmark data is further evaluated by a radiologist. Experimental results indicate that MediConfusion poses significant challenges to several existing VLMs, highlighting areas for improvement and setting the stage for future research.

strengths:
1. The paper addresses a well-motivated and underexplored problem in the medical domain.
2. The benchmark creation process is robust, with manual evaluation by a radiologist enhancing its credibility.
3. The experiments are comprehensive, demonstrating that MediConfusion presents substantial challenges to current VLMs, with promising potential for inspiring future research.

weaknesses:
While this work provides valuable insights, it appears to closely follow the Multimodal Visual Patterns (MMVP) benchmark framework, potentially limiting its novelty. Many findings align with known challenges in general VLMs.

questions:
1. Are there confusing pairs that appear visually similar but differ in feature space?
2. How would the Mixture-of-Features method from "Eyes Wide Shut? Exploring the Visual Shortcomings of Multimodal LLMs" apply to medical VLMs?
3. What are the limitations of the confusing pairs identified here? Could there be potential biases?
</content>
</thread_object>

</thread>
<thread>
creation date:
1730720319444

thread_type:
official_review

<thread_object>
creator: reviewer_qm8q

<content>
summary:
The paper introduces MediConfusion, a benchmark specifically designed to assess and expose failure modes in multimodal large language models (MLLMs) used in medical visual question answering (VQA) tasks. The benchmark highlights that current state-of-the-art MLLMs, including both open-source and proprietary models, struggle significantly with distinguishing visually dissimilar yet clinically distinct medical images, often performing below random guessing on the dataset. MediConfusion is created by identifying “confusing image pairs” from the ROCO radiology dataset, where image pairs appear distinct to medical professionals but prove challenging for MLLMs due to limitations in visual feature space alignment.

The authors reveal key failure patterns among MLLMs, such as difficulties in differentiating between normal and pathological anatomy, recognizing lesion characteristics, and identifying medical devices and vascular conditions. The benchmark leverages radiologist oversight to ensure clinical relevance and accuracy in the question-answer pairs, aiming to guide future MLLM improvements in medical contexts. By exposing these systematic vulnerabilities, the paper underscores the critical need for more reliable and trustworthy AI systems in healthcare applications.

strengths:
Originality: The paper addresses a critical gap in the assessment of medical MLLMs by introducing MediConfusion, a novel benchmark explicitly designed to test the reliability of these models in healthcare. While prior benchmarks focus on overall performance in typical medical scenarios, this work innovatively emphasizes systematic failure modes by identifying “confusing image pairs” that challenge models with subtle, clinically important distinctions. The benchmark not only probes weaknesses but also highlights specific visual reasoning failures, which is a unique contribution to medical AI evaluation.

Quality: The dataset creation is rigorous, combining automated techniques with expert radiologist validation to ensure that each question is clinically relevant and accurately represents medical knowledge. The experimental design is robust, systematically evaluating a range of state-of-the-art models (both general and medical-domain MLLMs) and comparing their performance against baseline expectations. The detailed breakdown of common model failure patterns enhances the paper’s depth, providing actionable insights for improving MLLM robustness in medical settings.

Clarity: The paper is well-structured and presents its findings in a clear, logical manner. Descriptions of the dataset creation process, evaluation methods, and results are easy to follow, with visual aids (e.g., figures illustrating confusing image pairs) that help readers understand the complexity of the visual tasks posed to models. The breakdown of error types further clarifies the distinct challenges MLLMs face, enhancing the reader’s comprehension of the benchmark’s significance.

Significance: The benchmark’s focus on failure modes has broad implications for the deployment of MLLMs in healthcare. By surfacing limitations that could compromise patient safety, the work serves as a foundational tool for future research aimed at increasing AI reliability in clinical practice. Additionally, MediConfusion highlights the limitations of current visual encoders and training paradigms in handling medical data, offering a clear research direction for building more robust and trustworthy models. The benchmark’s significance is further bolstered by its potential as a standard for evaluating and guiding improvements in medical AI systems.

weaknesses:
Limited Dataset Size: While the MediConfusion benchmark is rigorous, the dataset size (352 questions across 9 categories) may be relatively small to capture the full spectrum of medical image complexity. Expanding the dataset with a broader range of confusing image pairs, potentially covering additional anatomic regions and diagnostic subtleties, could improve its generalizability and make it more comprehensive for model evaluation across diverse medical contexts.

questions:
1.	Dataset Diversity and Expansion: Could you elaborate on the decision to limit the benchmark to the ROCO dataset? Do you have plans to expand MediConfusion to include other datasets, such as ultrasound or nuclear imaging, to capture a broader range of diagnostic tasks? Additional dataset diversity might reveal new model weaknesses or challenges in different medical imaging modalities.
	2.	Impact of Prompt Engineering: Given the importance of prompt phrasing in VQA tasks, did you experiment with alternative prompt formats or styles (e.g., framing questions in different ways or including detailed instructions)? If so, what impact did this have on model performance, and could further prompt optimization improve reliability? Insights here could guide future research on prompt refinement in medical VQA.
	3.	Future Directions for Medical MLLM Improvements: Given the identified failure patterns (e.g., difficulties with spatial reasoning or lesion characteristics), do you have specific recommendations for architectural or training adjustments that could address these weaknesses? For example, do you see value in integrating spatial attention mechanisms or training models on more anatomically detailed data?
</content>
</thread_object>

</thread>
<thread>
creation date:
1732240356193

thread_type:
official_comment

<thread_object>
creator: authors

<content>
title:
Summary of additional experiments (1)

comment:
We appreciate the time and effort of all reviewers and their insightful feedback. We did our best to address all concerns regarding our work. We performed additional experiments to reflect reviewer comments and updated the manuscript accordingly (highlighted in blue). The summary of new experiments is as follows:

1. **Prompt sensitivity:** As suggested by **Reviewer QM8Q**, we add an ablation study on the effect of manual prompt engineering on the performance of the models in Appendix C.  For this study, we create 10 variants of the multiple-choice input prompt and record the performance of GPT-4o, InstructBLIP, and LLaVA-Med. The table below shows the mean and standard deviation of the performance:

| Model         | Set Score (Mean) | Set Score (Std) |
|---------------|------------------|-----------------|
| GPT-4o        | 19.12           | 0.043           |
| InstructBLIP  | 4.79            | 0.116           |
| LLaVA-Med     | 0               | 0               |

We observe that GPT-4o performance is robust to prompt format, but the performance is still below random guessing. LLaVA-Med struggles with the multiple-choice format, and using different prompts does not resolve this issue. For InstructBLIP, the sensitivity to prompting is higher than GPT-4o, but its performance does not change drastically. Overall, we find that prompt format and style is likely not the root cause for poor performance on MediConfusion.

2. **Effect of dataset difficulty:** In Appendix E, we add a discussion on the effect of similarity thresholds on dataset difficulty based on **Reviewer cT2V**’s suggestion. We create an ‘easy’ version of the benchmark by specifically looking for image pairs that are dissimilar (cosine similarity below 0.4) in BiomedCLIP’s feature space. More details on dataset creation are included in the appendix.  We find that the performance of GPT-4o and LLaVA-Med increased significantly (to 98.38% and 33.91% set accuracy respectively):

| Model                | Easy Variant | Original MediConfusion |
|----------------------|--------------|------------------------|
| GPT-4o (MC eval.)    | 98.38        | 18.01                 |
| LLaVA-Med (PS eval.) | 34.21        | 1.14                   |

Our experiment demonstrates that models can indeed differentiate between image pairs in our confusing pair-based VQA format, if the images are different enough, as evidenced by the nearly 100% accuracy of GPT-4o on the easy variant. Thus, this experiment further supports the need for a strict selection criteria for confusing pairs, as easier variants of our VQA may be unable to identify the shortcomings of state-of-the-art models.

3. **Effect of fine-tuning:** Following the suggestion of **Reviewer 772B**, we add experiments on the effect of fine-tuning on MediConfusion in Appendix D. We follow standard procedure to fine-tune LLaVA-Med, consisting of fine-tuning the language model weights and the multimodal adapter, while the image encoder is frozen. We train on approx. half of MediConfusion samples and evaluate performance on the other half. The following table summarizes our results: 

| Epoch | Train Set Accuracy | Test Set Accuracy |
|-------|---------------------|-------------------|
| 20    | 15.48              | 6.52              |
| 40    | 54.76              | 18.48             |
| 60    | 59.52              | 20.65             |
| 80    | 66.67              | 19.57             |
| 100   | 63.10              | 20.65             |
| 1000  | 84.52              | 19.57             |

Our results show that even after 1000 epochs, the model cannot achieve 100% set accuracy on the training data, indicating that the inputs of some pairs are perceived as being too similar by the model to distinguish between them despite being distinct. Note that typical fine-tuning consists of between 1-50 epochs to avoid overfitting. Furthermore, the best test accuracy is around 20%, which is still well below random guessing. These results show that the model likely learned the multiple-choice format due to fine-tuning (improved accuracy from 0% to 20%), but otherwise the knowledge learned on the train set does not generalize, which strongly implies that vision embeddings are too ambiguous. This experiment suggests that MediConfusion can likely only be solved by improving the vision encoder directly.
</content>
</thread_object>

</thread>


Metareview:
metareview:
This is a datasets and benchmarks paper. The authors introduced MediConfusion, a challenging medical Visual Question Answering (VQA) benchmark dataset that probes the failure modes of medical MLLMs from a vision perspective. The benchmark dataset is designed to evaluate the ability of state-of-the-art models to recognize subtle yet clinically meaningful differences between medical images. Then, the dataset was further evaluated by a radiologist. The authors find that all tested MLLMs, open-source and proprietary, perform below random chance on MediConfusion, indicating some serious reliability problems on MLLMs. In sum: this is an interesting and timely paper on hot topics - medical MLLMs, the findings are unexpected - all models from GPT-4o, Gemini 1.5 Pro to Llava, InstructBLIP, achieve performance below random guessing on MediConfusion, and the code and data were provided with the paper. After the rebuttal stage, most reviewers supported this paper.