Towards context‐sensitive CT imaging — organ‐specific image formation for single (SECT) and dual energy computed tomography (DECT)

• Published in: Medical physics (Lancaster) 2018-10, Vol.45 (10), p.4541-4557
• Main Authors: Dorn, Sabrina, Chen, Shuqing, Sawall, Stefan, Maier, Joscha, Knaup, Michael, Uhrig, Monika, Schlemmer, Heinz‐Peter, Maier, Andreas, Lell, Michael, Kachelrieß, Marc
• Format: Article
• Language: English
• Subjects: CNN segmentation; dual energy; image display; image formation
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1002/mp.13127

Purpose The purpose of this study was to establish a novel paradigm to facilitate radiologists’ workflow — combining mutually exclusive CT image properties that emerge from different reconstructions, display settings and organ‐dependent spectral evaluation methods into a single context‐sensitive imaging by exploiting prior anatomical information. Methods The CT dataset is segmented and classified into different organs, for example, the liver, left and right kidney, spleen, aorta, and left and right lung as well as into the tissue types bone, fat, soft tissue, and vessels using a cascaded three‐dimensional fully convolutional neural network (CNN) consisting of two successive 3D U‐nets. The binary organ and tissue masks are transformed to tissue‐related weighting coefficients that are used to allow individual organ‐specific parameter settings in each anatomical region. Exploiting the prior knowledge, we develop a novel paradigm of a context‐sensitive (CS) CT imaging consisting of a prior‐based spatial resolution (CSR), display (CSD), and dual energy evaluation (CSDE). The CSR locally emphasizes desired image properties. On a per‐voxel basis, the reconstruction most suitable for the organ, tissue type, and clinical indication is chosen automatically. Furthermore, an organ‐specific windowing and display method is introduced that aims at providing superior image visualization. The CSDE analysis allows to simultaneously evaluate multiple organs and to show organ‐specific DE overlays wherever appropriate. The ROIs that are required for a patient‐specific calibration of the algorithms are automatically placed into the corresponding anatomical structures. The DE applications are selected and only applied to the specific organs based on the prior knowledge. The approach is evaluated using patient data acquired with a dual source CT system. The final CS images simultaneously link the indication‐specific advantages of different parameter settings and result in images combining tissue‐related desired image properties. Results A comparison with conventionally reconstructed images reveals an improved spatial resolution in highly attenuating objects and in air while the compound image maintains a low noise level in soft tissue. Furthermore, the tissue‐related weighting coefficients allow for the combination of varying settings into one novel image display. We are, in principle, able to automate and standardize the spectral analysis of the DE data using prior anatomical in