title: Image quality of virtual noncontrast images derived from dual-energy CT angiography after endovascular aneurysm repair.
abstract: OBJECTIVE
  To compare true and "virtual" noncontrast images derived from dual-energy CT examinations in patients after endovascular repair of aortic aneurysms.
  
  
  METHODS
  Seventy dual-energy CT examinations were performed on a dual-source CT scanner with a single-energy noncontrast scan and a dual-energy acquisition in venous phase. True and virtual noncontrast images were compared regarding image quality, calcifications in true noncontrast images, subtraction of calcification in virtual noncontrast images, and acceptance levels by two radiologists. Presence of endoleaks was assessed on venous-phase images and on virtual or true noncontrast images. In addition, the acceptance of color-coded images, in which iodine information is colored, was assessed. Possible dose reduction of a single-phase dual-energy examination protocol was compared with a standard biphasic examination protocol.
  
  
  RESULTS
  Twenty-four endoleaks were detected and correctly classified with both approaches. Mean image quality was rated good for virtual noncontrast images (1.97 +/- 0.99) and excellent for true noncontrast images (1.16 +/- 0.37; P< .0001). Ninety-four percent of virtual noncontrast images were rated as diagnostic, and 80% of all true noncontrast images showed calcifications within the aneurysm. Subtraction of calcification in virtual noncontrast images was classified as none (30%), minimal (40%), moderate (24%), or severe (6%). Eighty-three percent of color-coded images were rated as fully diagnostic, 11% were accepted with restrictions, and 6% were nondiagnostic. Possible dose reduction of a single-phase dual-energy protocol, compared with a standard biphasic protocol, was 44%.
  
  
  CONCLUSIONS
  Dual-energy CT makes a reliable detection of endoleaks feasible in a single acquisition. This provides a potential dose reduction for patients who have to undergo lifelong follow-up examinations after endovascular aneurysm repair.
authors.affiliation: Department of Clinical Radiology, University Hospitals Grosshadern, Ludwig-Maximilians University, Grosshadern Campus, Marchioninistr 15, 81377 Munich, Germany. wieland.sommer@med.uni-muenchen.de
authors.forename: Wieland H
authors.initials: WH
authors.lastname: Sommer
authors.forename: Anno
authors.initials: A
authors.lastname: Graser
authors.forename: Christoph R
authors.initials: CR
authors.lastname: Becker
authors.forename: Dirk A
authors.initials: DA
authors.lastname: Clevert
authors.forename: Maximilian F
authors.initials: MF
authors.lastname: Reiser
authors.forename: Konstantin
authors.initials: K
authors.lastname: Nikolaou
authors.forename: Thorsten R C
authors.initials: TR
authors.lastname: Johnson
mesh_terms: D000368:Aged; D000792:Angiography / Q000379:methods*; D017130:Angioplasty / Q000379:methods*; D001014:Aortic Aneurysm / Q000000981:diagnostic imaging* / Q000601:surgery*; D001027:Aortography / Q000379:methods*; D003287:Contrast Media; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome
chemical_list: D003287:Contrast Media