Towards context‐sensitive CT imaging — organ‐specific image formation for single (SECT) and dual energy computed tomography (DECT)
Authors: Dorn Sabrina , Chen Shuqing , Sawall Stefan , Maier Joscha , Knaup Michael , Uhrig Monika , Schlemmer Heinz‐Peter , Maier Andreas , Lell Michael , Kachelrieß Marc 
Published: August 2018

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 information. Each tissue type is evaluated with its corresponding DE application simultaneously.

Conclusion

This work provides a proof of concept of CS imaging. Since radiologists are not aware of the presented method and the tool is not yet implemented in everyday clinical practice, a comprehensive clinical evaluation in a large cohort might be topic of future research. Nonetheless, the presented method has potential to facilitate workflow in clinical routine and could potentially improve diagnostic accuracy by improving sensitivity for incidental findings. It is a potential step toward the presentation of evermore increasingly complex information in CT and toward improving the radiologists workflow significantly since dealing with multiple CT reconstructions may no longer be necessary. The method can be readily generalized to multienergy data and also to other modalities.