Ensuring quality for events of varying contrast agent in 3d dual-energy x-ray imaging

System (SYS) for image processing, comprising:

• an input interface (IN) for receiving, when the system is in use, a volume image reconstructed from spectrally processed projection data acquired by a spectral imaging apparatus (IA) whilst contrast agent is present in a field of view of the spectral imaging apparatus during acquisition;
• a segmentor (SC) component configured to segment the volume image for contrast agent contributions to obtain a segmented volume image;
• a forward-projector (FP) configured to forward-project the segmented volume image onto the spectrally processed projection data;
• a quality checker (QC) configured to establish quality indicator data indicative of a change of a concentration of the contrast agent in the field of view during the acquisition, based on a mismatch between the forward-projected segmented volume image, and the spectrally processed projection data, and
• an output interface (OUT) for providing output data including the quality indicator data.