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arxiv: 2603.19451 · v2 · submitted 2026-03-19 · 💻 cs.CV · cs.AI

LoFi: Location-Aware Fine-Grained Representation Learning for Chest X-ray

Pith reviewed 2026-05-15 08:05 UTC · model grok-4.3

classification 💻 cs.CV cs.AI
keywords chest x-rayfine-grained representationlocation-aware captioningphrase groundingimage retrievalvision-language modelcaptioning loss
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The pith

LoFi learns superior fine-grained chest X-ray representations by jointly optimizing location-aware captioning losses that supply region-level supervision.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper introduces LoFi to address the difficulty of capturing spatially confined clinical findings in chest X-rays for retrieval and phrase grounding tasks. It combines sigmoid, captioning, and location-aware captioning losses optimized together with a lightweight large language model. The location-aware captioning loss supplies region-level supervision through grounding and dense captioning objectives without needing explicit region annotations. These representations feed into a fine-grained encoder that is integrated with retrieval-based in-context learning. Experiments demonstrate improved performance on retrieval and phrase grounding using the MIMIC-CXR and PadChest-GR datasets.

Core claim

LoFi jointly optimizes sigmoid, captioning, and location-aware captioning losses with a lightweight LLM so that the location-aware captioning loss supplies region-level supervision through grounding and dense captioning objectives, thereby producing fine-grained representations that improve chest X-ray retrieval and phrase grounding.

What carries the argument

The location-aware captioning loss, which supplies region-level supervision through grounding and dense captioning objectives.

If this is right

  • Superior retrieval performance on MIMIC-CXR and PadChest-GR datasets.
  • Enhanced phrase grounding across diverse settings through integration of a fine-grained encoder with retrieval-based in-context learning.
  • Fine-grained representation learning without the need for explicit region annotations.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same loss structure may support spatially precise analysis in other medical imaging domains.
  • Lightweight LLM usage points to possible efficiency gains for clinical deployment.
  • Retrieval-based in-context learning may extend to few-shot diagnostic tasks in related imaging modalities.

Load-bearing premise

The location-aware captioning loss enables effective region-level supervision through grounding and dense captioning objectives without requiring explicit region annotations.

What would settle it

Direct experiments showing no performance gain over baselines on retrieval or phrase grounding tasks using MIMIC-CXR and PadChest-GR would falsify the central claim.

Figures

Figures reproduced from arXiv: 2603.19451 by Myeongkyun Kang, Xiaoxiao Li, Yanting Yang.

Figure 1
Figure 1. Figure 1: Illustration of (a) location-aware fine-grained representation learning [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Qualitative results with ground truth (dashed) and pre￾dictions (solid) [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Qualitative results with ground truth (dashed) and pre￾dictions (solid) [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: (a)-(d) Ablation results of our method using all losses (filled), without [PITH_FULL_IMAGE:figures/full_fig_p008_4.png] view at source ↗
read the original abstract

Fine-grained representation learning is crucial for retrieval and phrase grounding in chest X-rays, where clinically relevant findings are often spatially confined. However, the lack of region-level supervision in contrastive models and the limited ability of large vision language models to capture fine-grained representations in external validation lead to suboptimal performance on these tasks. To address these limitations, we propose Location-aware Fine-grained representation learning (LoFi), which jointly optimizes sigmoid, captioning, and location-aware captioning losses using a lightweight large language model. The location-aware captioning loss enables region-level supervision through grounding and dense captioning objectives, thereby facilitating fine-grained representation learning. Building upon these representations, we integrate a fine-grained encoder into retrieval-based in-context learning to enhance chest X-ray grounding across diverse settings. Extensive experiments demonstrate that our method achieves superior retrieval and phrase grounding performance on MIMIC-CXR and PadChest-GR.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript proposes LoFi, a method for fine-grained representation learning in chest X-rays. It jointly optimizes sigmoid, captioning, and location-aware captioning losses in a lightweight LLM, where the location-aware loss is intended to enable region-level supervision via grounding and dense captioning objectives. A fine-grained encoder is then integrated into retrieval-based in-context learning. The central claim is that this yields superior retrieval and phrase grounding performance on the MIMIC-CXR and PadChest-GR datasets.

Significance. If the location-aware captioning loss can be shown to deliver verifiable region-level supervision without explicit annotations, the approach would offer a practical advance for fine-grained medical vision-language tasks, improving retrieval and grounding while remaining computationally lightweight. The emphasis on joint optimization of multiple losses and integration with in-context learning is a reasonable direction, but the significance is currently difficult to evaluate given the absence of implementation details on spatial signal generation.

major comments (1)
  1. [§3] §3 (Method, location-aware captioning loss): the manuscript does not specify how spatial location signals are generated or injected into the loss (no bounding-box pseudo-labels, attention maps from a frozen detector, coordinate regression, or other mechanism is described). This is load-bearing for the central claim, as the asserted superiority on retrieval and phrase grounding is attributed to effective region-level supervision from this loss.
minor comments (2)
  1. [Abstract] Abstract: the claim of 'superior retrieval and phrase grounding performance' is stated without any quantitative numbers, baselines, or ablation results, which reduces the informativeness of the summary.
  2. [§3] The paper would benefit from a clear diagram or pseudocode showing the exact flow of the location-aware loss computation and how it interacts with the grounding/dense captioning objectives.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive feedback on our manuscript. We address the major comment below and will revise the manuscript to improve clarity and reproducibility.

read point-by-point responses
  1. Referee: [§3] §3 (Method, location-aware captioning loss): the manuscript does not specify how spatial location signals are generated or injected into the loss (no bounding-box pseudo-labels, attention maps from a frozen detector, coordinate regression, or other mechanism is described). This is load-bearing for the central claim, as the asserted superiority on retrieval and phrase grounding is attributed to effective region-level supervision from this loss.

    Authors: We agree that the current version of the manuscript does not provide sufficient detail on the generation and injection of spatial location signals into the location-aware captioning loss. This omission makes it difficult to fully evaluate the region-level supervision mechanism. In the revised manuscript, we will expand §3 to explicitly describe how spatial signals are produced (via pseudo-labels derived from the grounding and dense captioning objectives) and how they are incorporated into the loss computation. We believe this clarification will directly address the concern and strengthen support for the central claims regarding retrieval and phrase grounding performance. revision: yes

Circularity Check

0 steps flagged

No significant circularity; method is a training recipe without self-referential derivations

full rationale

The paper describes LoFi as jointly optimizing sigmoid, captioning, and location-aware captioning losses in a lightweight LLM, with the location-aware loss claimed to enable region-level supervision via grounding and dense captioning. No equations, derivations, or fitted parameters are presented that reduce any prediction or result to the inputs by construction. Performance claims rest on experimental results on MIMIC-CXR and PadChest-GR rather than any closed-form equivalence or self-citation chain. The approach is self-contained as an empirical training procedure without load-bearing self-referential steps.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The abstract does not introduce or rely on any explicit free parameters, axioms, or invented entities beyond standard assumptions of contrastive and captioning training.

pith-pipeline@v0.9.0 · 5455 in / 983 out tokens · 32458 ms · 2026-05-15T08:05:22.115780+00:00 · methodology

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Reference graph

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