title: Dual-energy CT in the assessment of mediastinal lymph nodes: comparative study of virtual non-contrast and true non-contrast images.
abstract: OBJECTIVE
  To evaluate the reliability of virtual non-contrast (VNC) images reconstructed from contrast-enhanced, dual-energy scans compared with true non-contrast (TNC) images in the assessment of high CT attenuation or calcification of mediastinal lymph nodes.
  
  
  METHODS
  A total of 112 mediastinal nodes from 45 patients who underwent non-contrast and dual-energy contrast-enhanced scans were analyzed. Node attenuation in TNC and VNC images was compared both objectively, using computed tomography (CT) attenuation, and subjectively, via visual scoring (0, attenuation ≤ the aorta; 1, > the aorta; 2, calcification). The relationship among attenuation difference between TNC and VNC images, CT attenuation in TNC images, and net contrast enhancement (NCE) was analyzed.
  
  
  RESULTS
  CT attenuation in TNC and VNC images showed moderate agreement (intraclass correlation coefficient, 0.612). The mean absolute difference was 7.8 ± 7.6 Hounsfield unit (HU) (range, 0-36 HU), and the absolute difference was equal to or less than 10 HU in 65.2% of cases (73/112). Visual scores in TNC and VNC images showed fair agreement (κ value, 0.335). Five of 16 nodes (31.3%) which showed score 1 (n = 15) or 2 (n = 1) in TNC images demonstrated score 1 in VNC images. The TNC-VNC attenuation difference showed a moderate positive correlation with CT attenuation in TNC images (partial correlation coefficient [PCC] adjusted by NCE: 0.455) and a weak negative correlation with NCE (PCC adjusted by CT attenuation in TNC: -0.245).
  
  
  CONCLUSIONS
  VNC images may be useful in the evaluation of mediastinal lymph nodes by providing additional information of high CT attenuation of nodes, although it is underestimated compared with TNC images.
authors.affiliation: Department of Radiology, School of Medicine, Ewha Womans University, Seoul 158-710, Korea.
authors.forename: Seon Young
authors.initials: SY
authors.lastname: Yoo
authors.forename: Yookyung
authors.initials: Y
authors.lastname: Kim
authors.forename: Hyun Hae
authors.initials: HH
authors.lastname: Cho
authors.forename: Mi Joo
authors.initials: MJ
authors.lastname: Choi
authors.forename: Sung Shine
authors.initials: SS
authors.lastname: Shim
authors.forename: Jeong Kyong
authors.initials: JK
authors.lastname: Lee
authors.forename: Seung Yon
authors.initials: SY
authors.lastname: Baek
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002114:Calcinosis / Q000000981:diagnostic imaging*; D003287:Contrast Media; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008198:Lymph Nodes / Q000000981:diagnostic imaging*; D008297:Male; D008482:Mediastinum / Q000000981:diagnostic imaging*; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media
keywords: Chest; Dual-energy CT; Iodine subtraction; Lymph nodes; Virtual non-contrast