title: Retinal vascular fractal dimension measurement and its influence from imaging variation: results of two segmentation methods.
abstract: OBJECTIVE
  To assess the influences of imaging variation (different photographic angle) on the measurement of retinal vascular fractal dimension (D(f)), using two segmentation methods.
  
  
  METHODS
  Nonlinear orthogonal projection segmentation (International Retinal Imaging Software-Fractal, termed IRIS-Fractal) and curvature-based segmentation (Singapore Institute Vessel Assessment-Fractal, termed SIVA-Fractal) methods were used to measure D(f) and were assessed for their reproducibility in detecting retinal vessels of 30 stereoscopic pairs of optic disc color images. Each pair was taken from the same eye with slightly different angles of incidence. Each photograph of the pairs had subtle variations in brightness between areas temporal and nasal to the optic disc.
  
  
  RESULTS
  Intragrader reproducibility of D(f) measurement was similar (intraclass correlation 0.81 and 0.96, respectively) for IRIS-Fractal and SIVA-Fractal. Within-image pair Pearson's correlation coefficients (r) of D(f) measurements were moderate for both methods (0.57 and 0.48, respectively).
  
  
  CONCLUSIONS
  Both nonlinear orthogonal projection and curvature-based retinal vessel segmentation methods were found to be sensitive to variations in image brightness, resulting from iris shadowing associated with different angle of photographic incidence.
authors.affiliation: Centre for Eye Research Australia, Department of Ophthalmology, University of Sydney, Sydney, Australia.
authors.forename: Victoria Fay
authors.initials: VF
authors.lastname: Cosatto
authors.forename: Gerald
authors.initials: G
authors.lastname: Liew
authors.forename: Elena
authors.initials: E
authors.lastname: Rochtchina
authors.forename: Alan
authors.initials: A
authors.lastname: Wainwright
authors.forename: YongPing
authors.initials: Y
authors.lastname: Zhang
authors.forename: Wynne
authors.initials: W
authors.lastname: Hsu
authors.forename: Mong Li
authors.initials: ML
authors.lastname: Lee
authors.forename: Qiangfeng Peter
authors.initials: QP
authors.lastname: Lau
authors.forename: Haslina H
authors.initials: HH
authors.lastname: Hamzah
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.forename: Jie Jin
authors.initials: JJ
authors.lastname: Wang
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D017709:Fractals; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000098:blood supply*; D010781:Photography; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000033:anatomy & histology*