Compression-Driven Anomaly Detection in Brain MRI Using an Interpretable Quantum Autoencoder
This work addresses the challenge of unsupervised anomaly detection in brain MRI, where ground-truth anomaly labels are unavailable, by proposing an interpretable quantum autoencoder-based method. The approach maps image patches to quantum states via angle encoding and employs a variational encoder–decoder architecture augmented with auxiliary “junk” qubits to enable controllable information compression. Anomaly scores are defined based on the incompressibility of inputs relative to normal data. The study highlights the critical role of encoder–decoder asymmetry in detection performance and supports principled threshold selection. Evaluated on public datasets, the model achieves slice-level ROC-AUC of approximately 0.95 and patch-level ROC-AUC of about 0.813, outperforming classical autoencoder and PCA baselines, while producing localized anomaly heatmaps that align well with tumor regions.