Predicting 30-Day Mortality in Elderly Hip Fracture Patients Using Multimodal Machine Learning

Core Concepts

A multimodal deep learning model combining pre-operative static patient data, hip and chest images, and per-operative vital signs and medication data can predict 30-day mortality in elderly hip fracture patients.

Abstract

The authors developed a multimodal deep learning model to predict 30-day mortality in elderly hip fracture patients. The model combines the following data modalities:
Pre-operative data:

Static patient data (demographics, daily living activities, nutrition, surgery information, lab results, medication, and comorbidities)
Hip and chest X-ray images
Per-operative data:

Vital signs (heart rate, pulse, oxygen saturation, blood pressure)
Medication data
The authors trained unimodal models for each data modality and then fused them into a multimodal model. They found that:

The pre-operative static patient data was the most important modality, contributing 70.3% to the mortality prediction on average.
Adding per-operative data (vitals and medication) did not significantly improve the performance compared to the pre-operative multimodal model.
The multimodal model achieved an average test set AUC of 0.78, which is on par with state-of-the-art models using only pre-operative data.
The authors applied Shapley value analysis to explain the multimodal model's predictions, showing that static features related to kidney function and self-reliance were most important.

The results suggest that pre-operative data, especially static patient data, is the most important for predicting 30-day mortality in elderly hip fracture patients. The authors propose future work to further improve the model by addressing overfitting and missing data issues.

Stats

The 30-day mortality rate in the dataset is 7.8% (131 out of 1669 patients).
The average age of patients is 83 years, with 71.2% females and 28.8% males.

Quotes

"An accurate risk score computed using data known before surgery (pre-operative data) can lead to better information about the patient and be of help in the treatment selection."
"Clinicians use multiple data sources in their decision-making, therefore multimodal models should in theory be better at making these complex predictions."

Key Insights Distilled From

Feature importance to explain multimodal prediction models. A clinical use case

by Jorn-Jan van... at arxiv.org 04-30-2024

https://arxiv.org/pdf/2404.18631.pdf

Deeper Inquiries

How could the multimodal model be further improved to better handle missing data and reduce overfitting?

To improve the multimodal model's handling of missing data and reduce overfitting, several strategies can be implemented:

Robustness to Missing Data: The model can be made more robust against missing data by incorporating techniques such as data imputation, where missing values are filled in using statistical methods or machine learning algorithms. Additionally, the model can be designed to handle missing data gracefully during training and inference, ensuring that instances with missing modalities are still considered in the prediction process.

Feature Selection: To prevent overfitting, feature selection techniques can be applied to identify the most relevant features for prediction. By focusing on a subset of important features, the model can reduce complexity and improve generalization to unseen data.

Regularization: Regularization techniques like L2 regularization can be used to penalize large weights in the model, preventing overfitting. Dropout layers can also be added to introduce randomness and prevent the model from memorizing the training data.

Fusion Methods: Exploring different fusion methods, such as late fusion or bottleneck fusion, can help optimize the integration of information from different modalities. Late fusion allows for combining predictions from individual models, while bottleneck fusion restricts cross-modal information flow to focus on essential features.

How could the explainability of the multimodal model be extended to provide more detailed insights into the contributions of individual features and their interactions across modalities?

To enhance the explainability of the multimodal model and provide more detailed insights into the contributions of individual features and their interactions across modalities, the following approaches can be considered:

Local Explanations: Provide detailed local explanations for individual predictions, showing how each feature contributes to the final prediction for a specific instance. This can help clinicians understand the reasoning behind each prediction and identify critical features influencing the outcome.

Interaction Analysis: Explore the interactions between features across different modalities to uncover complex relationships that impact the prediction. Techniques like SHAP (SHapley Additive exPlanations) can be used to analyze feature interactions and their combined effects on the model's predictions.

Feature Importance Propagation: Develop methods to propagate feature importance values through the multimodal model to understand the relative contributions of features from different modalities. This can help in identifying the most influential features and their impact on the prediction outcome.

Visualization Techniques: Utilize visualization techniques such as feature importance plots, SHAP summary plots, and interaction heatmaps to present the explainability of the model in a clear and interpretable manner. Visual representations can aid in conveying complex relationships between features and predictions to clinicians and stakeholders.