title: [Virtual unenhanced images derived from spectral CT imaging accessing gastric carcinoma: a feasible study].
abstract: OBJECTIVE
  To qualitatively and quantitatively compare MSI images and WB images derived from spectral CT imaging with CU images in accessing gastric carcinoma.
  
  
  METHODS
  The clinical data and imaging findings of 91 cases of gastric carcinomas between December 2013 and May 2015 were analyzed retrospectively. All patients underwent CU CT and enhanced CT with spectral imaging in AP and VP. MSI images were reconstructed based on monochromatic images of 70 keV in AP. WB images were obtained by water-iodine pair substance isolation of the AP images. Two abdominal radiologists independently evaluated the image quality and the depiction of gastric carcinoma in CU, MSI and WB images using a 5-point scale. The sensitivities of gastric cancer were evaluated by using enhanced images as the reference standard.The CT number of various regions, image noise, relative enhancement CT value of tumors and metastasis were measured and calculated on CU and MSI images. The CNR of gastric tumor were measured on CU, MSI and WB images. Effective radiation doses for triple-phase and dual-phase scan were calculated. Differences were tested for statistical significance using the Wilcoxon's signed rank test and the paired t-test.
  
  
  RESULTS
  Interobserver agreement with regard to image quality and the depiction of gastric carcinoma was good(all kappa>0.70). There was no statistical significant difference in image quality between CU(4.30±0.63) and MSI(4.17±0.58) images(P>0.05), both higher than WB(3.87±0.84) images (both P<0.01). The depiction of gastric carcinoma in CU(3.86±0.50) and MSI(3.73±0.55) images had no statistical significant difference (P>0.05), and both higher than WB(3.34±0.38) images( both P<0.01). The sensitivities of CU, MSI and WB images were 91.2%, 95.6%, 93.4%. The CT number of gastric tumors, liver metastasis and aorta, image noise on MSI images were slightly higher than on TNE images(P<0.05). The CT number of gastric tumors, liver metastasis and aorta, image noise on MSI images were slightly higher than on TNE images(P<0.05). The CT number of lymph nodes, liver and muscle, CT relative enhancement value of gastric tumors, lymph nodes and liver metastasis had no significant difference between TNE and MSI images (all P>0.05). The CNR of gastric tumors had significant difference between groups: WB images were higher than MSI and MSI were higher than CU images(all P<0.01). The dose saving by removing the CU was 8.2 mSv(32%).
  
  
  CONCLUSIONS
  The MSI images derived from spectral CT can provide comparable image quality to CU images and reliable diagnostic information for gastric tumors, which is superior to WB images, replacing CU images will lower radiation exposure by 32%.
authors.affiliation: Department of Radiology, First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China.
authors.forename: Yaru
authors.initials: Y
authors.lastname: Chai
authors.forename: Jianbo
authors.initials: J
authors.lastname: Gao
authors.forename: Jingjing
authors.initials: J
authors.lastname: Xing
authors.forename: Pan
authors.initials: P
authors.lastname: Liang
authors.forename: Peijie
authors.initials: P
authors.lastname: Lü
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Chen
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D008198:Lymph Nodes; D012189:Retrospective Studies; D013274:Stomach Neoplasms; D014057:Tomography, X-Ray Computed