title: [Fractal analysis of retinal vascular tree: segmentation and estimation methods].
abstract: OBJECTIVE
  Although it has been proposed that retinal vasculature is fractal, no method of standardization has been performed for vascular segmentation or for dimension calculation, thus resulting in great variability among values of fractal dimensions. The present study was designed to determine if estimation of retinal vessel fractal dimensions is dependent on vascular segmentation and dimensional calculation methods.
  
  
  METHODS
  Ten eye fundus images were segmented to extract their vascular trees by four computational methods ("multi-threshold", "scale-space", "pixel classification" and "ridge based detection"). Their information, mass-radius and box counting fractal dimensions were calculated and compared with those of the same vascular trees manually segmented (gold standard).
  
  
  RESULTS
  The mean vascular tree dimension varied among the groups of different segmentation methods, from 1.39 to 1.47 for box counting, from 1.47 to 1.52 for information and from 1.48 to 1.57 for mass-radius dimensions. The utilization of different vascular segmentation methods and different dimension calculation methods introduced significant difference among fractal dimension of vessels.
  
  
  CONCLUSIONS
  Estimation of retinal vessel fractal dimensions was dependent on both vascular segmentation and dimension calculation methods.
authors.affiliation: Universidade Federal do Rio Grande do Norte, Natal, RN, Brasil. mendoncaoftalmo@yahoo.com.br
authors.forename: Marcelo Bezerra de Melo
authors.initials: MB
authors.lastname: de Mendonça
authors.forename: Carlos Alexandre
authors.initials: CA
authors.lastname: de Amorim Garcia
authors.forename: Romildo de Albuquerque
authors.initials: Rde A
authors.lastname: Nogueira
authors.forename: Marcelo Andrade Filgueira
authors.initials: MA
authors.lastname: Gomes
authors.forename: Marcelo Morais
authors.initials: MM
authors.lastname: Valença
authors.forename: Fernando
authors.initials: F
authors.lastname: Oréfice
mesh_terms: D000293:Adolescent; D000328:Adult; D017709:Fractals; D006801:Humans; D007091:Image Processing, Computer-Assisted; D012171:Retinal Vessels / Q000033:anatomy & histology*