2.5D Top-K Ranked Multiple Instance Learning to Classify NSCLC PD-L1 Status on CT Images

Classifying the status of NSCLC PD-L1 on chest CT is a cost-effective and non-invasive method. The existing multiple instance learning (MIL) methods are not effective for this task, due to the lack of an efficient feature encoder for 3D instances and ignoring the importance of representative instance selection. Thus, they cannot capture weak visual cues related to PD-L1 status on CT images. To address this, we propose a 2.5D top-K ranked multiple instance learning method. We design a 2.5D instance feature encoder, which takes advantage of knowledge from a 2D pre-trained model and has trainable parameters to learn information for 3D instances. In addition, we design a top-K ranked multiple instance learning strategy, which fully exploits the bag-level labels to select representative instances to eliminate the effect of atypical instances and guide the network to learn effective information. We demonstrate that our method can not only outperform state-of-the-art MIL methods on the PD-L1 status classification but also generalize well on a COVID-19 classification task.