Ding Y, et al. - A total of 200 people with non-contrast and portal-venous phase spectral-detector CT (SDCT) were retrospectively randomized to a test and a validation group of 100 persons each in order to examine the relationship of vertebral CT attenuation between virtual non-contrast (VNC) and true non-contrast (TNC) images and to assess whether VNC vertebral CT attenuation could be used for phantom-less osteoporosis identification in dual-layer SDCT. In both groups, CT attenuation was lower in VNC vs TNC. VNC and TNC CT attenuation was robustly related. Using the regression equation established in the test group, in the validation group, the prognosticated TNC CT attenuation did not vary from the real TNC CT attenuation. A VNC CT attenuation cut-off of 52HU gave an AUC of 0.978 for osteoporosis identification. Thus, in VNC vs TNC images, L1 CT attenuation is systematically underestimated. Nevertheless, TNC L1 CT attenuation can be prognosticated safely from VNC. Moreover, in phantom-less osteoporosis disocvery, VNC may do well.