title: Hepatic MR angiography: a multiobserver comparison of visualization methods.
abstract: OBJECTIVE
  MR angiography (MRA) is an established diagnostic method; however, controversy remains over the best technique for display. In this study, we compared five methods of depicting hepatic MRA, including a novel skeletonization approach, using receiver operator characteristic (ROC) curves, interobserver variability (kappa values), and speed of interpretation.
  
  
  METHODS
  Twenty-one patients scheduled for isolated liver perfusion therapy for metastatic disease underwent contrast-enhanced three-dimensional MRA to determine vascular anatomy. Vascular anatomy was validated at the time of surgery. We displayed the image data, using five techniques: maximum intensity projection, targeted maximum intensity projection, isointensity surface (isosurface), connected isointensity surface (connected isosurface), and ordered region growing skeleton (skeleton). Four observers, blinded to the surgical results, interpreted each technique in random order without patient identifiers. Areas under the ROC curves, kappa values of interobserver variability, and time to interpret each display were compared.
  
  
  RESULTS
  Skeletonized MRA had the highest area under the ROC curve (A(z), 0.90 +/- 0.04) compared with the other techniques (p < 0.013). Kappa scores of agreement were also highest for skeletonized MRA (0.75 +/- 0.04) and had no overlap at the 95% confidence level compared with other techniques. Compared with source images, all visualization methods were faster to interpret, but the skeleton technique was more quickly (p = 0.04) interpreted than the other techniques.
  
  
  CONCLUSIONS
  Skeletonized MRA with the skeleton connectivity algorithm is a semi-automated method of displaying complex arterial anatomy. Compared with other techniques, it is more accurate, more consistent among observers, and slightly faster to interpret. Skeletonization should be applicable to CT angiography and MRA.
authors.affiliation: Diagnostic Radiology Department, The Clinical Center, National Institutes of Health, Bldg. 10, Rm. 1C660, Bethesda, MD 20892-1182, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Choyke
authors.forename: P
authors.initials: P
authors.lastname: Yim
authors.forename: H
authors.initials: H
authors.lastname: Marcos
authors.forename: V B
authors.initials: VB
authors.lastname: Ho
authors.forename: R
authors.initials: R
authors.lastname: Mullick
authors.forename: R M
authors.initials: RM
authors.lastname: Summers
mesh_terms: D005260:Female; D006499:Hepatic Artery / Q000000981:diagnostic imaging*; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D012372:ROC Curve; D011859:Radiography