Solving Sample-Level Out-of-Distribution Detection on 3D Medical Images

Deep Learning (DL) models tend to perform poorly when the data comes from a distribution different from the training one. In critical applications such as medical imaging, out-of-distribution (OOD) detection helps to identify such data samples, increasing the model's reliability. Recent works have developed DL-based OOD detection that achieves promising results on 2D medical images. However, scaling most of these approaches on 3D images is computationally intractable. Furthermore, the current 3D solutions struggle to achieve acceptable results in detecting even synthetic OOD samples. Such limited performance might indicate that DL often inefficiently embeds large volumetric images. We argue that using the intensity histogram of the original CT or MRI scan as embedding is descriptive enough to run OOD detection. Therefore, we propose a histogram-based method that requires no DL and achieves almost perfect results in this domain. Our proposal is supported two-fold. We evaluate the performance on the publicly available datasets, where our method scores 1.0 AUROC in most setups. And we score second in the Medical Out-of-Distribution challenge without fine-tuning and exploiting task-specific knowledge. Carefully discussing the limitations, we conclude that our method solves the sample-level OOD detection on 3D medical images in the current setting.Comment: 20 pages, 3 figures, submitted to Computerized Medical Imaging and Graphic

Performance-oriented dependency parsing

In the last decade a lot of dependency parsers have been developed. This book describes the motivation for the development of yet another parser - MDParser. The state of the art is presented and the deficits of the current developments are discussed. The main problem of the current parsers is that the task of dependency parsing is treated independently of what happens before and after it. However, in practice parsing is rarely done for the sake of parsing itself, but rather in order to use the results in a follow-up application. Additionally, current parsers are accuracy-oriented and focus only on the quality of the results, neglecting other important properties, especially efficiency. The evaluation of some NLP technologies is sometimes as difficult as the task itself. For dependency parsing it was long thought not to be the case, however, some recent works show that the current evaluation possibilities are limited. This book proposes a methodology to account for the weaknesses and combine the strengths of the current approaches. Finally, MDParser is evaluated against other state-of-the-art parsers. The results show that it is the fastest parser currently available and it is able to process plain text, which other parsers usually cannot. The results are slightly behind the top accuracies in the field, however, it is demonstrated that it is not decisive for applications