Bag of temporal co-occurrence words for retrieval of focal liver lesions using 3D multiphase contrast-enhanced CT images

Computer-aided diagnosis (CAD) systems have been verified to have the potential to assist radiologists in clinical diagnosis to detect and characterize focal liver lesions (FLLs) based on single- or multiphase contrast-enhanced computed tomography (CT) images. Features extracted from multiphase contrast-enhanced CT images carry more important diagnostic information i.e. enhancement pattern and demonstrate much stronger discriminative ability compared to those of single-phase CT images. In this paper, we propose a new method for multiphase image feature generation called the bag of temporal co-occurrence words (BoTCoW). A temporal co-occurrence image connecting intensity from multiphase images is constructed. Then the bag of visual word (BoVW) model is employed on the temporal co-occurrence images to extract temporal features. The proposed method effectively captures temporal enhancement information and demonstrates the distribution of the evolution patterns. The effectiveness of this method is validated in a retrieval system using 132 FLLs with confirmed pathology type. The preliminary results show that the proposed BoTCoW method outperforms the previously proposed temporal features and multiphase features based on the BoVW model.