Abstract
Purpose
Radiologists interpret many medical images and clinical practice demands timely interpretation, resulting in a heavy workload. To reduce the workload, here we formulate and validate a method that can handle different types of medical image and can detect virtually all types of lesion in a medical image. For the first time, we show that two flow-based deep generative (FDG) models can predict the logarithm posterior probability in a semi-supervised approach.
Methods
We adopt two FDG models in conjunction with Bayes’ theorem to predict the logarithm posterior probability that a medical image is normal. We trained one of the FDG models with normal images and the other FDG model with normal and non-normal images.
Results
We validated the method using two types of medical image: chest X-ray images (CXRs) and brain computed tomography images (BCTs). The area under the receiver operating characteristic curve for pneumonia-like opacities in CXRs was 0.839 on average, and for infarction in BCTs was 0.904.
Conclusion
We formulated a method of predicting the logarithm posterior probability using two FDG models. We validated that the method can detect abnormal findings in CXRs and BCTs with both an acceptable performance for testing and a comparatively light workload for training.



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The dataset of chest X-ray images is open to the public and known as the Radiological Society of North America (RSNA) Pneumonia Detection Challenge dataset. The dataset of brain-computed tomography images is protected under the laws of our institution; hence, it is not open to the public.
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Funding
The Department of Computational Diagnostic Radiology and Preventive Medicine, The University of Tokyo Hospital, is sponsored by HIMEDIC Inc. and Siemens Healthcare K.K. This work was supported in part by JSPS Grants-in-Aid for Scientific Research (KAKENHI Grant Nos. 18K12095 and 18K12096). This work was also supported by the Joint Usage/Research Center for Interdisciplinary Large-scale Information Infrastructures and High Performance Computing Infrastructure projects in Japan (Project IDs: jh190047-DAH and jh200042-DAH).
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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1975 Helsinki Declaration, as revised in 2008(5).
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We slightly modified Glow software by Open AI, which is currently open to the public on GitHub (https://github.com/openai/glow), although our code is currently not open to the public.
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Shibata, H., Hanaoka, S., Nomura, Y. et al. Versatile anomaly detection method for medical images with semi-supervised flow-based generative models. Int J CARS 16, 2261–2267 (2021). https://doi.org/10.1007/s11548-021-02480-4
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DOI: https://doi.org/10.1007/s11548-021-02480-4