Recent study results have show that medical imaging can be used for the diagnosis of COVID-19 [17] . Moreover, two recent studies indicate that COVID-19 is possibly better diagnosed with radiological imaging when compared to the PCR-Test [12, 16] . To classify computer tomography (CT) images of COVID-19 cases automatically, a Convolutional Neural Network has been used in [18] . The study aimed to answer the questions, if artificial intelligence technology can be used to early screen COVID-19 patients from their CT images and what is the corresponding diagnostic accuracy. The study also focused on the development of an early screening model to distinguish COVID-19 pneumonia from Influenza-A viral pneumonia and healthy cases. The experiments showed that the overall accuracy was 86.7% from the perspective of CT cases as a whole.
Recently, a call has been launched for scientists working in the field of artificial intelligence to focus their research and knowledge on the current coronavirus crisis [1] . At the moment, there is a lack of sufficiently large and publicly available records of image data. Data is, however, essential for machine learning techniques. With the intention to simplify the access to currently publicly available image data and metadata we started this survey.
At present, medical capacities are severely limited in many countries. Also, the flow of information and exchange between physicians and scientists is limited due to the lockdowns in various countries. More massive data sets with image data of COVID-19 cases are, therefore, either not available or not publicly accessible. However, since these data sets are urgently needed to support the diagnosis and treatment of COVID-19 with machine learning or artificial intelligence technologies, we would like to contribute with this initiative to the full exploration and further development of the currently available potential of different technologies.
Since the authors are currently working on the detection of COVID-19 with machine learning themselves, this survey will be updated regularly. We would be very grateful if members of the community could share sources with us, which are not yet listed here. Please report all errors to our email addresses. We will fix them as soon as possible. With this initiative, we also would like to encourage all scientists to make their data sets publicly available to the community, provided that data protection allows it. This initiative can also be supported by making it better known with a citation. Table 1 shows a list of resources and datasets which provide publicly accessible medical imaging data of COVID-19 cases. The types of data are classified by CT, X-Ray, magnetic resonance tomography (MRT), metadata of the corresponding patient/case, and case review. The respective classes are annotated with Y for yes, N for no and U for unknown.
We would like to point out not to claim any form of diagnostic performance of models until clinical studies have been performed.