---
tags:
- chest-xray
- radiology
- phrase-grounding
- mimic-cxr
license: apache-2.0
---

# LAPVQA — Phrase Grounding

Part of the [LAPVQA collection](https://huggingface.co/collections/dmusingu/lapvqa).

## Description

TransVG-style phrase grounding heads trained on MIMIC-CXR, predicting the bounding
box of a described abnormality given the chest X-ray and a text phrase.
Each checkpoint is a dict: `{state_dict, vis_dim, txt_dim, d_model, num_layers, encoder, epoch, val_miou, val_acc50}`.

## Architecture — `VisualGroundingHead`

```
vis_proj   : Linear(vis_dim → 256)
txt_proj   : Linear(txt_dim → 256)
reg_token  : Parameter [1, 1, 256]
sequence   : [REG | vis_tokens | txt_token]
transformer: 3 × TransformerEncoderLayer (self-attn, pre-norm)
box_head   : MLP(256 → 256 → 4)   # sigmoid → (cx,cy,w,h) ∈ [0,1]
```

## Results (MIMIC-CXR test set)

**Zero-shot:** mIoU ≈ 0.082–0.089 across all encoders.

**Fine-tuned (MAE-ViT-L/16):** mIoU 0.320, Acc@0.25 0.569, Pointing Acc 0.593.

| File | Encoder | vis_dim | txt_dim |
|---|---|---|---|
| `clip-vit-l14.pt` | CLIP ViT-L/14 | 1024 | 768 |
| `siglip.pt` | SigLIP | 1152 | 1152 |
| `florence2.pt` | Florence-2 | 1024 | 768 |
| `coca.pt` | CoCa | 768 | 768 |
| `owlv2.pt` | OWLv2 | 1024 | 768 |
| `mae-vit-l16.pt` | MAE ViT-L/16 | 1024 | 768 |

## Loading

```python
import torch
from lapvqa.pg.heads import VisualGroundingHead

ckpt = torch.load("mae-vit-l16.pt", map_location="cpu")
head = VisualGroundingHead(
    vis_dim    = ckpt["vis_dim"],
    txt_dim    = ckpt["txt_dim"],
    d_model    = ckpt["d_model"],
    num_layers = ckpt["num_layers"],
)
head.load_state_dict(ckpt["state_dict"])
head.eval()

with torch.no_grad():
    # vis_tokens: [B, HW, vis_dim] — spatial patch tokens from frozen encoder
    # txt_vec:    [B, txt_dim]     — pooled text representation from frozen encoder
    pred_boxes = head(vis_tokens, txt_vec)  # [B, 4] (cx,cy,w,h) in [0,1]
```