title: Fractal dimension analysis of the cortical ribbon in mild Alzheimer's disease.
abstract: Fractal analysis methods are used to quantify the complexity of the human cerebral cortex. Many recent studies have focused on high resolution three-dimensional reconstructions of either the outer (pial) surface of the brain or the junction between the gray and white matter, but ignore the structure between these surfaces. This study uses a new method to incorporate the entire cortical thickness. Data were obtained from the Alzheimer's Disease (AD) Neuroimaging Initiative database (Control N=35, Mild AD N=35). Image segmentation was performed using a semi-automated analysis program. The fractal dimension of three cortical models (the pial surface, gray/white surface and entire cortical ribbon) were calculated using a custom cube-counting triangle-intersection algorithm. The fractal dimension of the cortical ribbon showed highly significant differences between control and AD subjects (p<0.001). The inner surface analysis also found smaller but significant differences (p<0.05). The pial surface dimensionality was not significantly different between the two groups. All three models had a significant positive correlation with the cortical gyrification index (r>0.55, p<0.001). Only the cortical ribbon had a significant correlation with cortical thickness (r=0.832, p<0.001) and the Alzheimer's Disease Assessment Scale cognitive battery (r=-0.513, p=0.002). The cortical ribbon dimensionality showed a larger effect size (d=1.12) in separating control and mild AD subjects than cortical thickness (d=1.01) or gyrification index (d=0.84). The methodological change shown in this paper may allow for further clinical application of cortical fractal dimension as a biomarker for structural changes that accrue with neurodegenerative diseases.
authors.affiliation: Department of Neurology, University of Utah, USA. richard.king@hsc.utah.edu
authors.forename: Richard D
authors.initials: RD
authors.lastname: King
authors.forename: Brandon
authors.initials: B
authors.lastname: Brown
authors.forename: Michael
authors.initials: M
authors.lastname: Hwang
authors.forename: Tina
authors.initials: T
authors.lastname: Jeon
authors.forename: Anuh T
authors.initials: AT
authors.lastname: George
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000473:pathology* / Q000523:psychology; D002540:Cerebral Cortex / Q000473:pathology*; D016208:Databases, Factual; D005260:Female; D017709:Fractals; D006179:Gyrus Cinguli / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009483:Neuropsychological Tests; D012372:ROC Curve; D015203:Reproducibility of Results; D012727:Sex Characteristics