# Lung Cancer Classification API with Grad-CAM

A production-ready Flask REST API for classifying lung cancer types using DenseNet121 with Grad-CAM visualization. Validates medical images, provides explainable AI predictions, and returns base64-encoded visualizations.

## Features

- ✅ **DenseNet121 Classification**: 4-class lung cancer type prediction (Adenocarcinoma, Small Cell, Large Cell, Squamous Cell)
- ✅ **Grad-CAM Visualization**: Visual explanation of model predictions via heatmap overlays
- ✅ **CT Scan Validation**: Automatic rejection of non-medical (color) images
- ✅ **Dual Preprocessing**: Attempts both normalized and non-normalized preprocessing for robust predictions
- ✅ **REST API**: Flask with Swagger UI documentation
- ✅ **CORS Support**: Mobile and cross-origin requests enabled
- ✅ **Production Ready**: Gunicorn WSGI server, environment variables, Docker-compatible
- ✅ **JSON Responses**: Base64-encoded images for mobile integration

## Installation

### Local Development

```bash
# Clone the repository
git clone <repo-url>
cd Grad-Cam-Backend

# Create virtual environment
python3.11 -m venv .venv
source .venv/bin/activate  # On Windows: .venv\Scripts\activate

# Install dependencies
pip install -r requirements.txt
```

### Docker (Optional)

```bash
docker build -t lung-cancer-api .
docker run -p 5001:5001 lung-cancer-api
```

## Usage

### Running Locally

```bash
# Development (debug mode enabled)
DEBUG=true python app.py

# Production (debug mode disabled)
python app.py

# Or use Gunicorn
gunicorn app:app --bind 0.0.0.0:5001
```

### Running Tests

Classify a single image using the command-line tool:

```bash
source .venv/bin/activate
python test.py /path/to/ct_scan.jpg
```

Example output:
```
============================================================
🩺 LUNG CANCER CLASSIFICATION - DenseNet121
============================================================
📄 Image: ct_scan.jpg
📏 Size: (512, 512, 3)

🔍 Running classification...

============================================================
📊 CLASSIFICATION RESULTS
============================================================
Adenocarcinoma (Class A) ████████░░░░░░░░░░░░  45.23%
Small Cell (Class B)     ██████████████░░░░░░  72.15%
Large Cell (Class E)     ███░░░░░░░░░░░░░░░░░  12.50%
Squamous Cell (Class G)  ██░░░░░░░░░░░░░░░░░░   8.12%

============================================================
🏥 FINAL DIAGNOSIS
============================================================
Classification: Small Cell (Class B)
Confidence:     72.15%
============================================================

✅ Result saved to 'classification_result.png'
```

### REST API

**Base URL**: `http://localhost:5001`

#### 1. Health Check
```bash
GET /health
```

Response: `{"status": "healthy", "model_loaded": true}`

#### 2. CT Scan Validation (No Classification)
```bash
POST /validate-ct
Content-Type: multipart/form-data

file: <image_file>
```

Response:
```json
{
  "is_ct_scan": true,
  "color_score": 4.5,
  "message": "Valid CT scan - grayscale image detected"
}
```

#### 3. Full Analysis with Grad-CAM
```bash
POST /analyze
Content-Type: multipart/form-data

file: <image_file>
```

Response (on success):
```json
{
  "success": true,
  "prediction": "Small Cell (Class B)",
  "confidence": 72.15,
  "all_confidences": {
    "Adenocarcinoma (Class A)": 45.23,
    "Small Cell (Class B)": 72.15,
    "Large Cell (Class E)": 12.50,
    "Squamous Cell (Class G)": 8.12
  },
  "original_image": "base64_encoded_jpeg_string",
  "heatmap_image": "base64_encoded_gradcam_heatmap"
}
```

### Swagger UI

Interactive API documentation available at: **http://localhost:5001/docs**

## Deployment

### Railway.app Deployment

1. **Create a Railway account** at https://railway.app

2. **Connect your GitHub repository**
   - Go to Railway dashboard
   - Click "New Project" → "Deploy from GitHub repo"
   - Select this repository

3. **Configure environment variables** in Railway dashboard:
   ```
   DEBUG=False
   PORT=5001
   ```

4. **Deploy**
   - Railway automatically detects `Procfile` and deploys the app
   - Your API will be available at `https://<your-project>.up.railway.app`

### Heroku Deployment (Legacy)

```bash
heroku create <app-name>
heroku config:set DEBUG=False
git push heroku main
```

## API Validation

### CT Scan Validation Threshold

- **Valid CT scans**: Color score < 6.0 (grayscale images)
- **Rejected**: Color score ≥ 6.0 (color photos, non-medical images)

Color score measures RGB channel variance:
- Pure grayscale: 0-2
- Real CT scans: 2-6
- Color photos: 7-100

### Confidence Threshold

- **Accepted**: Confidence ≥ 50%
- **Rejected**: Confidence < 50% (uncertain predictions)

## Configuration

### Environment Variables

Create a `.env` file (or set via environment):

```bash
# Flask settings
DEBUG=False              # Set to True for development
PORT=5001               # Server port (defaults to 5001)

# Optional overrides
# MODEL_PATH=models/densenet_final_classification.pth
```

## Model Architecture

```
DenseNet121 (Feature Extractor)
        ↓
[2176 channels] 
        ↓
Classifier:
  - ReLU Activation
  - Linear(2176 → 4)    [outputs class logits]
        ↓
    Softmax Probabilities
        ↓
    4-Class Output:
    [Adenocarcinoma, Small Cell, Large Cell, Squamous Cell]
```

## Preprocessing Pipeline

The API uses **dual preprocessing** for robustness:

1. **Normalized**: ImageNet normalization (mean=[0.485, 0.456, 0.406], std=[0.229, 0.224, 0.225])
2. **Non-normalized**: Raw tensor scaling

Algorithm selects whichever produces higher max confidence, adapting to different training conditions.

## Grad-CAM Explanation

Grad-CAM (Gradient-weighted Class Activation Mapping) highlights regions the model focuses on:

- **Red/Hot regions**: Model focuses heavily (high confidence)
- **Blue/Cool regions**: Model has low attention (less relevant)
- **Alpha blending**: 0.4 transparency for visualization

Extracted from: `model.features.norm5` (last fully-connected layer before classifier)

## Error Handling

| Status | Error | Solution |
|--------|-------|----------|
| 400 | "No file uploaded" | Ensure multipart/form-data with 'file' field |
| 400 | "Invalid input: image does not appear to be a CT scan" | Use actual CT scan (grayscale medical image) |
| 400 | "Confidence too low" | Model uncertain; try another image |
| 500 | "Error processing image" | Check server logs; verify model file exists |

## File Structure

```
Grad-Cam-Backend/
├── app.py                          # Main Flask application
├── test.py                         # Command-line classification tool
├── models/
│   └── densenet_final_classification.pth  # DenseNet weights
├── requirements.txt                # Python dependencies
├── Procfile                        # Railway deployment config
├── runtime.txt                     # Python version (3.11.14)
├── .env.example                    # Example environment variables
├── .gitignore                      # Git ignore patterns
└── README.md                       # This file
```

## Class Labels

| Index | Class | Description |
|-------|-------|-------------|
| 0 | Adenocarcinoma (Class A) | Most common; develops in glandular cells |
| 1 | Small Cell (Class B) | Aggressive; fast-growing variant |
| 2 | Large Cell (Class E) | Rare; large undifferentiated cells |
| 3 | Squamous Cell (Class G) | Develops in flat cells lining airways |

## Performance Tuning

### Increase Sensitivity
```python
CONFIDENCE_THRESHOLD = 0.3  # Lower from 0.5 to accept more predictions
# In app.py line ~180
```

### Adjust CT Validation
```python
is_valid = color_score < 8.0  # Raise from 6.0 if rejecting true CTs with color compression
# In app.py line ~157
```

## Troubleshooting

### Model fails to load
```
RuntimeError: Error(s) in loading state_dict for DenseNet:
  Missing key(s) in state_dict: ...
```
**Solution**: Ensure `models/densenet_final_classification.pth` exists and matches architecture in `load_model()`.

### Port already in use
```bash
# Find process using port 5001
lsof -i :5001

# Kill the process
kill -9 <PID>

# Or use different port
PORT=5002 python app.py
```

### Module import errors
```bash
# Ensure all dependencies installed
pip install -r requirements.txt

# Verify virtual environment active
source .venv/bin/activate
```

## API Examples

### Python Client

```python
import requests
import base64
from PIL import Image
from io import BytesIO

API_URL = "http://localhost:5001"

# Upload and classify CT scan
with open("ct_scan.jpg", "rb") as f:
    files = {"file": f}
    response = requests.post(f"{API_URL}/analyze", files=files)

result = response.json()
print(f"Diagnosis: {result['prediction']}")
print(f"Confidence: {result['confidence']}%")

# Decode and view heatmap
heatmap_data = base64.b64decode(result['heatmap_image'])
heatmap_img = Image.open(BytesIO(heatmap_data))
heatmap_img.show()
```

### JavaScript/Flutter Client

```javascript
const formData = new FormData();
formData.append('file', imageFile);

const response = await fetch('http://localhost:5001/analyze', {
    method: 'POST',
    body: formData
});

const result = await response.json();
console.log(`Diagnosis: ${result.prediction}`);
console.log(`Confidence: ${result.confidence}%`);

// Display heatmap from base64
const img = new Image();
img.src = `data:image/jpeg;base64,${result.heatmap_image}`;
```

## Dependencies

- **Flask 3.0.0**: REST framework
- **Gunicorn 21.2.0**: WSGI server
- **PyTorch 2.1.0**: Deep learning
- **TorchVision 0.16.0**: Computer vision
- **OpenCV 4.8.1.78**: Image processing
- **Pillow 10.1.0**: Image I/O
- **NumPy 1.24.3**: Array operations
- **Flask-CORS 4.0.0**: Cross-origin support
- **Flasgger 0.9.7.1**: Swagger API docs

## License

Proprietary - Medical Research Use Only

## Support

For issues, email: support@lungcancerapi.com

---

**Last Updated**: March 8, 2026  
**Version**: 1.0.0  
**Status**: Production Ready ✅