  Obtaining models that capture imaging markers relevant for disease
progression and treatment monitoring is challenging. Models are typically based
on large amounts of data with annotated examples of known markers aiming at
automating detection. High annotation effort and the limitation to a vocabulary
of known markers limit the power of such approaches. Here, we perform
unsupervised learning to identify anomalies in imaging data as candidates for
markers. We propose AnoGAN, a deep convolutional generative adversarial network
to learn a manifold of normal anatomical variability, accompanying a novel
anomaly scoring scheme based on the mapping from image space to a latent space.
Applied to new data, the model labels anomalies, and scores image patches
indicating their fit into the learned distribution. Results on optical
coherence tomography images of the retina demonstrate that the approach
correctly identifies anomalous images, such as images containing retinal fluid
or hyperreflective foci.
