app.py

import gradio as gr
import torch
import numpy as np
import os
import nibabel as nib
import torchio
import torch.nn as nn
import subprocess
import spaces  # Import spaces for GPU decoration
from scipy.ndimage.measurements import center_of_mass
from huggingface_hub import hf_hub_download
from monai.transforms import Compose, LoadImaged, Spacingd, CropForegroundd, SpatialPadd, CenterSpatialCropd
from monai.data import Dataset, DataLoader
from nnunet_mednext import create_mednext_encoder_v1

# Model and data directory setup
MODEL_DIR = "/root/.cache/huggingface/hub"
DATASET_DIR = os.path.join(MODEL_DIR, "BrainAgeNeXt")
REPO_ID = "FrancescoLR/BrainAgeNeXt"

# Ensure model directory exists
os.makedirs(MODEL_DIR, exist_ok=True)

# 🔹 Function to Download Model Weights from Hugging Face
def download_model():
    if not os.path.exists(DATASET_DIR):
        os.makedirs(DATASET_DIR, exist_ok=True)
        print("Downloading BrainAgeNeXt model weights...")
        for i in range(1, 6):
            hf_hub_download(repo_id=REPO_ID, filename=f"BrainAge_{i}.pth", cache_dir=MODEL_DIR)
        print("BrainAgeNeXt model downloaded successfully.")

# 🔹 Function to Load Model
def initialize_model():
    model_paths = [hf_hub_download(repo_id=REPO_ID, filename=f"BrainAge_{i}.pth", cache_dir=MODEL_DIR) for i in range(1, 6)]
    
    models = []
    for model_path in model_paths:
        model = MedNeXtEncReg().to(device)
        model.load_state_dict(torch.load(model_path, map_location=device))
        model.eval()
        models.append(model)
    return models

# 🔹 Define Model
class MedNeXtEncReg(nn.Module):
    def __init__(self):
        super(MedNeXtEncReg, self).__init__()
        self.mednextv1 = create_mednext_encoder_v1(
            num_input_channels=1, num_classes=1, model_id='B', kernel_size=3, deep_supervision=True
        )
        self.global_avg_pool = nn.AdaptiveAvgPool3d((1, 1, 1))
        self.regression_fc = nn.Sequential(
            nn.Linear(512, 64),
            nn.ReLU(),
            nn.Dropout(0.0),
            nn.Linear(64, 1)
        )

    def forward(self, x):
        x = self.mednextv1(x)
        x = self.global_avg_pool(x)
        x = torch.flatten(x, start_dim=1)
        age_estimate = self.regression_fc(x)
        return age_estimate.squeeze()

# 🔹 Preprocessing Pipeline
def prepare_transforms():
    return Compose([
        LoadImaged(keys=["image"], ensure_channel_first=True),
        Spacingd(keys=["image"], pixdim=(1.0, 1.0, 1.0)),
        CropForegroundd(keys=["image"], allow_smaller=True, source_key="image"),
        SpatialPadd(keys=["image"], spatial_size=(160, 192, 160)),
        CenterSpatialCropd(keys=["image"], roi_size=(160, 192, 160)),
        torchio.transforms.ZNormalization(masking_method=lambda x: x > 0, keys=["image"])
    ])

# 🔹 Process MRI File
def preprocess_mri(nifti_path):
    transforms = prepare_transforms()
    data_dict = {"image": nifti_path}
    dataset = Dataset([data_dict], transform=transforms)
    dataloader = DataLoader(dataset, batch_size=1, num_workers=0)
    return next(iter(dataloader))["image"].to(device)

# 🔹 Run Brain Age Prediction (Decorated for GPU Execution)
@spaces.GPU(duration=90)
def predict_brain_age(nifti_file, actual_age, sex):
    if not os.path.exists(nifti_file.name):
        return "Error: MRI file not found"

    # Load Model
    models = initialize_model()

    # Preprocess MRI
    image = preprocess_mri(nifti_file.name)

    # Run Predictions
    predictions = []
    with torch.no_grad():
        for model in models:
            pred = model(image)
            predictions.append(pred.cpu().numpy())

    # Compute Median Brain Age Prediction
    predicted_brain_age = np.median(np.stack(predictions))

    # Apply Correction Based on Actual Age
    predicted_brain_age_corrected = (
        predicted_brain_age + (actual_age * 0.062) - 2.96 if actual_age > 18 else predicted_brain_age
    )

    brain_age_difference = predicted_brain_age - actual_age
    # Determine color: Red if positive, Green if negative
    color = "red" if brain_age_difference > 0 else "green"
    bad_output_html = f"<span style='color:{color}; font-weight:bold;'>Brain Age Difference: {brain_age_difference:.2f} years</span>"

    # Return formatted outputs
    return f"Predicted Brain Age: {predicted_brain_age_corrected:.2f} years", bad_output_html

# 🔹 Gradio Interface Setup
with gr.Blocks() as demo:
    gr.Markdown("""
    # 🧠 **BrainAgeNeXt**: Advancing Brain Age Modeling
    Upload a preprocessed T1w MRI scan (.nii.gz), enter the age and sex of the subject, and get the brain age prediction.

    The following preprocessing steps are required.
    1. Skull-stripping using [SynthStrip](https://surfer.nmr.mgh.harvard.edu/docs/synthstrip/) with the `--no-csf` flag for optimal results.
    2. N4 bias field correction using [ANTs](https://github.com/ANTsX/ANTs/wiki/N4BiasFieldCorrection).
    3. Affine registration to the MNI 1mm isotropic template space. 

    **BrainAgeNeXt** has been trained and validated using over 11,000 T1w MRI acquired at 1.5, 3, and 7T. A 1mm isotropic resolution is preferred for the input image but not required. Our [manuscript](https://doi.org/10.1162/imag_a_00487) presents a detailed explanation of **BrainAgeNeXt** and its potential applications.
    """)

    with gr.Row():
        with gr.Column(scale=1):
            mri_input = gr.File(label="Upload a T1w MRI (NIfTI .nii.gz)")
            age_input = gr.Number(label="Enter Age", value=50)
            sex_input = gr.Radio(["Male", "Female"], label="Select Sex")
            submit_button = gr.Button("Predict")

        with gr.Column(scale=2):
            brain_age_output = gr.Textbox(label="Predicted Brain Age", interactive=False)
            bad_output = gr.HTML(label="Brain Age Difference")  # Use gr.HTML for colored text

    submit_button.click(
        fn=predict_brain_age,
        inputs=[mri_input, age_input, sex_input],
        outputs=[brain_age_output, bad_output]
    )

    gr.Markdown("""
    **Disclaimer:** This is a research tool and is not intended for clinical use.

    **If you find this tool useful, please consider citing:**
    1. La Rosa, F., Dos Santos Silva, J., Dereskewicz, E., Invernizzi, A., Cahan, N., Galasso, J., ... & Beck, E. S. (2025).
    BrainAgeNeXt: Advancing Brain Age Modeling for Individuals with Multiple Sclerosis. Imaging Neuroscience. 
   DOI: [10.1162/imag_a_00487](https://doi.org/10.1162/imag_a_00487)
    2. Roy, S., Koehler, G., Ulrich, C., Baumgartner, M., Petersen, J., Isensee, F., Jaeger, P.F. & Maier-Hein, K. (2023).
       MedNeXt: Transformer-driven Scaling of ConvNets for Medical Image Segmentation. 
       International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI).
    """)
# 🔹 Debugging GPU Environment
if torch.cuda.is_available():
    print(f"GPU available: {torch.cuda.get_device_name(0)}")
    device = torch.device("cuda")
else:
    print("No GPU detected. Falling back to CPU.")
    os.system("nvidia-smi")
    device = torch.device("cpu")
    
# 🔹 Download Model Weights
download_model()

# 🔹 Run Gradio App
if __name__ == "__main__":
    demo.launch(share=True)