Unsupervised Lesion Detection via Image Restoration with a Normative Prior

TL;DR

This paper introduces an unsupervised lesion detection method in medical images that models healthy anatomy with a probabilistic network prior, reducing false positives and outperforming existing methods.

Contribution

It proposes a novel MAP-based image restoration approach using a network prior for pixel-wise lesion detection, addressing false positives in prior-projection methods.

Findings

Outperforms state-of-the-art unsupervised methods by +0.13 AUC on brain MRI datasets.

Reduces false positives compared to prior-projection approaches.

Effective in detecting gliomas and stroke lesions in MRI images.

Abstract

Unsupervised lesion detection is a challenging problem that requires accurately estimating normative distributions of healthy anatomy and detecting lesions as outliers without training examples. Recently, this problem has received increased attention from the research community following the advances in unsupervised learning with deep learning. Such advances allow the estimation of high-dimensional distributions, such as normative distributions, with higher accuracy than previous methods.The main approach of the recently proposed methods is to learn a latent-variable model parameterized with networks to approximate the normative distribution using example images showing healthy anatomy, perform prior-projection, i.e. reconstruct the image with lesions using the latent-variable model, and determine lesions based on the differences between the reconstructed and original images. While being promising, the prior-projection step often leads to a large number of false positives. In this work, we approach unsupervised lesion detection as an image restoration problem and propose a probabilistic model that uses a network-based prior as the normative distribution and detect lesions pixel-wise using MAP estimation. The probabilistic model punishes large deviations between restored and original images, reducing false positives in pixel-wise detections. Experiments with gliomas and stroke lesions in brain MRI using publicly available datasets show that the proposed approach outperforms the state-of-the-art unsupervised methods by a substantial margin, +0.13 (AUC), for both glioma and stroke detection. Extensive model analysis confirms the effectiveness of MAP-based image restoration.