Objective To explore the value of spectral CT imaging in the preoperative evaluation on histodifferentiation of rectal adenocarcinoma.Methods 90 patients with rectal adenocarcinoma underwent dual-phase enhanced spectral CT scan,and were divided into well,moderately and poorly differentiated adenocarcinoma groups according to the pathology.Single-energy images with energy levels from 40 to 140 keV were generated by GSI Viewer software,and the slope K value of the energy curves were calculated.Iodine concentrations were derived from iodine-based material-separation images and normalized to the iodine concentrations in the aorta. ROC curves were derived to evaluate the differentiation diagnosis efficiency of normalized iodine concentration (NIC)and slope K in rectal adenocarcinoma,respectively.Results There were 22,50 and 18 cases in the well,moderately and poorly differentiated group,respectively.The iodine concentration,NIC and slope K value were statistically different both in the arterial and venous phase (P<0.05).According to the ROC curve,the diagnostic value of NIC was close to that of the slope K,with the sensitivity>76% and the specificity>74% in the arterial phase,and the sensitivity>77% and the specificity>70% in the venous phase by choo-sing the appropriate threshold.Conclusion The spectral CT can provide a new method for preoperatively evaluating the histodiffer-entiation of rectal adenocarcinoma.