title: Automated segmentation of cerebral vasculature with aneurysms in 3DRA and TOF-MRA using geodesic active regions: an evaluation study.
abstract: OBJECTIVE
  To evaluate the suitability of an improved version of an automatic segmentation method based on geodesic active regions (GAR) for segmenting cerebral vasculature with aneurysms from 3D x-ray reconstruction angiography (3DRA) and time of flight magnetic resonance angiography (TOF-MRA) images available in the clinical routine.
  
  
  METHODS
  Three aspects of the GAR method have been improved: execution time, robustness to variability in imaging protocols, and robustness to variability in image spatial resolutions. The improved GAR was retrospectively evaluated on images from patients containing intracranial aneurysms in the area of the Circle of Willis and imaged with two modalities: 3DRA and TOF-MRA. Images were obtained from two clinical centers, each using different imaging equipment. Evaluation included qualitative and quantitative analyses of the segmentation results on 20 images from 10 patients. The gold standard was built from 660 cross-sections (33 per image) of vessels and aneurysms, manually measured by interventional neuroradiologists. GAR has also been compared to an interactive segmentation method: isointensity surface extraction (ISE). In addition, since patients had been imaged with the two modalities, we performed an intermodality agreement analysis with respect to both the manual measurements and each of the two segmentation methods.
  
  
  RESULTS
  Both GAR and ISE differed from the gold standard within acceptable limits compared to the imaging resolution. GAR (ISE) had an average accuracy of 0.20 (0.24) mm for 3DRA and 0.27 (0.30) mm for TOF-MRA, and had a repeatability of 0.05 (0.20) mm. Compared to ISE, GAR had a lower qualitative error in the vessel region and a lower quantitative error in the aneurysm region. The repeatability of GAR was superior to manual measurements and ISE. The intermodality agreement was similar between GAR and the manual measurements.
  
  
  CONCLUSIONS
  The improved GAR method outperformed ISE qualitatively as well as quantitatively and is suitable for segmenting 3DRA and TOF-MRA images from clinical routine.
authors.affiliation: Center for Computational Imaging and Simulation Technologies in Biomedicine, Universitat Pompeu Fabra and Networking Biomedical Research Center on Bioengineering, Biomaterials and Nanomedicine, Barcelona 08018, Spain. hrvoje.bogunovic@upf.edu
authors.forename: Hrvoje
authors.initials: H
authors.lastname: Bogunović
authors.forename: José María
authors.initials: JM
authors.lastname: Pozo
authors.forename: María Cruz
authors.initials: MC
authors.lastname: Villa-Uriol
authors.forename: Charles B L M
authors.initials: CB
authors.lastname: Majoie
authors.forename: Rene
authors.initials: R
authors.lastname: van den Berg
authors.forename: Hugo A F
authors.initials: HA
authors.lastname: Gratama van Andel
authors.forename: Juan M
authors.initials: JM
authors.lastname: Macho
authors.forename: Jordi
authors.initials: J
authors.lastname: Blasco
authors.forename: Luis San
authors.initials: LS
authors.lastname: Román
authors.forename: Alejandro F
authors.initials: AF
authors.lastname: Frangi
mesh_terms: D000328:Adult; D000368:Aged; D000792:Angiography / Q000379:methods*; D001331:Automation; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods* / Q000592:standards; D002532:Intracranial Aneurysm / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012015:Reference Standards; D015203:Reproducibility of Results; D012189:Retrospective Studies