title: Standardized volume rendering for magnetic resonance angiography measurements in the abdominal aorta.
abstract: OBJECTIVE
  To compare three methods for standardizing volume rendering technique (VRT) protocols by studying aortic diameter measurements in magnetic resonance angiography (MRA) datasets.
  
  
  METHODS
  Datasets from 20 patients previously examined with gadolinium-enhanced MRA and with digital subtraction angiography (DSA) for abdominal aortic aneurysm were retrospectively evaluated by three independent readers. The MRA datasets were viewed using VRT with three different standardized transfer functions: the percentile method (Pc-VRT), the maximum-likelihood method (ML-VRT), and the partial range histogram method (PRH-VRT). The aortic diameters obtained with these three methods were compared with freely chosen VRT parameters (F-VRT) and with maximum intensity projection (MIP) concerning inter-reader variability and agreement with the reference method DSA.
  
  
  RESULTS
  F-VRT parameters and PRH-VRT gave significantly higher diameter values than DSA, whereas Pc-VRT gave significantly lower values than DSA. The highest interobserver variability was found for F-VRT parameters and MIP, and the lowest for Pc-VRT and PRH-VRT. All standardized VRT methods were significantly superior to both MIP and F-VRT in this respect. The agreement with DSA was best for PRH-VRT, which was the only method with a mean error below 1 mm and which also had the narrowest limits of agreement (95% of cases between 2.1 mm below and 3.1 mm above DSA).
  
  
  CONCLUSIONS
  All the standardized VRT methods compare favorably with MIP and VRT with freely selected parameters as regards interobserver variability. The partial range histogram method, although systematically overestimating vessel diameters, gives results closest to those of DSA.
authors.affiliation: Department of Radiology, Center for Medical Image Science and Visualization, Linköping University Hospital, Sweden. anders.persson@cmiv.liu.se
authors.forename: A
authors.initials: A
authors.lastname: Persson
authors.forename: T B
authors.initials: TB
authors.lastname: Brismar
authors.forename: C
authors.initials: C
authors.lastname: Lundström
authors.forename: N
authors.initials: N
authors.lastname: Dahlström
authors.forename: F
authors.initials: F
authors.lastname: Othberg
authors.forename: O
authors.initials: O
authors.lastname: Smedby
mesh_terms: D000704:Analysis of Variance; D015901:Angiography, Digital Subtraction; D017544:Aortic Aneurysm, Abdominal / Q000473:pathology*; D003287:Contrast Media; D019786:Gadolinium DTPA; D006801:Humans; D021621:Imaging, Three-Dimensional; D018810:Magnetic Resonance Angiography / Q000592:standards*; D015588:Observer Variation; D012189:Retrospective Studies
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA