Quantitative evaluation of the effects of dual-energy CT acquisition, reconstruction and postprocessing parameters on virtual Non-Calcium (VNCa) images

PURPOSE: The appearance and associated interpretation of Virtual Non-Calcium (VNCa) images extracted from dual-energy CT (DECT) acquisitions are influenced by many parameters. This study aimed to investigate the effects of acquisition, reconstruction, and postprocessing parameters on VNCa images.

MATERIAL AND METHODS: A human cadaver leg was scanned using a dual-source DECT scanner, with variations in tube current, tube voltage, reconstruction kernels, and post-processing settings (resolution, upper threshold, lower threshold, beam-hardening correction). The impact of noise was investigated by scanning the specimen five times using the same standard acquisition, reconstruction and postprocessing parameters. VNCa values were measured in four different regions of interest within different bones.

RESULTS: Tube current and reconstruction kernels had no significant effect on VNCa values, with maximal standard deviations of 6.2 and 6.1 HU respectively. However, reducing the kVp difference between both tubes, reduced the spectral separation which resulted in lower VNCa values. For postprocessing parameters, variations in resolution and lower and upper thresholds as well as applying beam-hardening correction showed a large impact on VNCa values.

CONCLUSION: The results of this study improve the understanding of the impact of certain CT parameters on VNCa images. Tube voltage and post-processing settings have a large impact on VNCa values. An inappropriate choice of threshold range, resolution and incorrect use of calcium beam-hardening correction can potentially lead to false positive findings of bone marrow edema. This can furthermore impact the ability to compare results from the literature and between institutions, which emphasizes the importance of optimizing and standardizing acquisition, reconstruction and postprocessing parameters for consistent VNCa imaging.