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Implicit Field Learning for Unsupervised Anomaly Detection in Medical Images

Naval Marimont, S. & Tarroni, G. (2021). Implicit Field Learning for Unsupervised Anomaly Detection in Medical Images. Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 12902, pp. 189-198. doi: 10.1007/978-3-030-87196-3_18


We propose a novel unsupervised out-of-distribution detection method for medical images based on implicit fields image representations. In our approach, an auto-decoder feed-forward neural network learns the distribution of healthy images in the form of a mapping between spatial coordinates and probabilities over a proxy for tissue types. At inference time, the learnt distribution is used to retrieve, from a given test image, a restoration, i.e. an image maximally consistent with the input one but belonging to the healthy distribution. Anomalies are localized using the voxel-wise probability predicted by our model for the restored image. We tested our approach in the task of unsupervised localization of gliomas on brain MR images and compared it to several other VAE-based anomaly detection methods. Results show that the proposed technique substantially outperforms them (average DICE 0.640 vs 0.518 for the best performing VAE-based alternative) while also requiring considerably less computing time.

Publication Type: Article
Additional Information: This version of the contribution has been accepted for publication, after peer review but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: Use of this Accepted Version is subject to the publisher’s Accepted Manuscript terms of use
Publisher Keywords: Anomaly detection, Unsupervised learning, Implicit fields, Occupancy networks
Subjects: Q Science > QA Mathematics > QA75 Electronic computers. Computer science
R Medicine > R Medicine (General)
Departments: School of Science & Technology > Computer Science
[thumbnail of MICCAI 2021 Implicit fields for unsup anom detection vFinal.pdf]
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