How can virtual no-contrast images be created?

The following question has been sent by xinsier:

Dear professor,
As I am a new learner of the DECT, I would like to know how the virtual no-contrast images be created? And is there any concrete calculation method?
thank you!

Sandra Halliburton, Cardiac Imaging Scientist, Cleveland, OH (USA):

Virtual non-contrast images can be generated using “Liver VNC” from Dual Energy software (syngo, Siemens).  The default settings of the Liver VNC can be modified to customize dual-energy image post-processing.

1. Measure attenuation (HU) of contrast agent in lumen in both 80 and 140 kVp images and calculate the ratio as HU_80/HU_140.  Replace the default “ratio” (default = 2) in the “Liver VNC” window with this new ratio value.
2. Replace the default maximum threshold value of 3071 (attenuation value above which voxels will excluded from processing) with a lower value (may be like 700 or 800). Ensure that contrast attenuation in 80 kVp is lower than this maximum threshold value.