Purpose: To investigate whether dual-energy CT(DECT)could help detect the invasiveness of pure ground-glass nodules(pGGNs)with diameter less than 10mm.Materials and methods: Thirty two patients with pGGNs of diameter less than 10mm detected by CT plain scan underwent contrast enhanced CT scans with spectral imaging mode before lung resection.And then,these pGGNs were divided into two groups as pre-invasive group(atypical adenomatous hyperplasia(AAH)and adenocarcinoma in situ(AIS))and invasive group(minimally invasive adenocarcinomas(MIA)and invasive adenocarcinomas(IAC))according to the pathologic results.Two radiologists expert in lung imaging ignoring of the pathologic results measured the maximum diameter and mean attenuation value of the nodules; the measured values were averaged for each nodule.They visually assessed the images for consensus with respect to lobulation,vacuole,pleural retraction using a 2-point scale,and the relationship between GGNs and bronchi or vascular respectively divided into five and four types.Chi-square test was used to compare these morphologic parameters.Spectral CT imaging were evaluated on the Gemstone Spectral Imaging viewer,and iodine concentration(IC)on iodine-based material decomposition images and CT numbers on monochromatic image sets to generate spectral HU curve were measured.Normalized IC(NIC)and spectral HU curve slope(λHU)was calculated using the following formula: NIC=IClesion/ICaorta and λHU=|CT40keV-CT100keV|/60.The two-sample t test was used to compare quantitative parameters.Results: There were 36 nodules confirmed by lung resection.Among them,25 were noninvasive(69.4%,6 AAH,19 AIS)and 11 were invasive(30.6%,7 MIA and 4 IAC).The diameters of invasive group were significantly greater than the pre-invasive group: 7.0±2.0mm vs.8.5±1.6mm,p=0.024.Both in pre-invasive and invasive group,the performances of lobulation were common,but vacuole and pleural retraction were fewer,and most small GGNs were seen vessels going through nodules without any morphological changes and the bronchi circumventing nodules.However,the differences between the two group were not obvious.The CT numbers acquired in plain CT imaging were-498.10±100.11 of pre-invasive group and-492.02±131.42 in invasive group.After contrast enhancement,GGNs were seen enhancement,with NIC of 0.61±0.22 in pre-invasive group and 0.58±0.24 in invasive group.However,no significant differences were shown.Conclusions: When small pGGNs of diameter less than 10mm were evaluated,the greater of diameters were,the more likely to be invasive.And although the nodules are small,enhancement could be evaluated by the DECT.