title: Wavelet entropy of BOLD time series: An application to Rolandic epilepsy.
abstract: To assess the wavelet entropy for the characterization of intrinsic aberrant temporal irregularities in the time series of resting-state blood-oxygen-level-dependent (BOLD) signal fluctuations. Further, to evaluate the temporal irregularities (disorder/order) on a voxel-by-voxel basis in the brains of children with Rolandic epilepsy.
  
  
  
  The BOLD time series was decomposed using the discrete wavelet transform and the wavelet entropy was calculated. Using a model time series consisting of multiple harmonics and nonstationary components, the wavelet entropy was compared with Shannon and spectral (Fourier-based) entropy. As an application, the wavelet entropy in 22 children with Rolandic epilepsy was compared to 22 age-matched healthy controls. The images were obtained by performing resting-state functional magnetic resonance imaging (fMRI) using a 3T system, an 8-element receive-only head coil, and an echo planar imaging pulse sequence ( T2*-weighted). The wavelet entropy was also compared to spectral entropy, regional homogeneity, and Shannon entropy.
  
  
  
  Wavelet entropy was found to identify the nonstationary components of the model time series. In Rolandic epilepsy patients, a significantly elevated wavelet entropy was observed relative to controls for the whole cerebrum (P = 0.03). Spectral entropy (P = 0.41), regional homogeneity (P = 0.52), and Shannon entropy (P = 0.32) did not reveal significant differences.
  
  
  
  The wavelet entropy measure appeared more sensitive to detect abnormalities in cerebral fluctuations represented by nonstationary effects in the BOLD time series than more conventional measures. This effect was observed in the model time series as well as in Rolandic epilepsy. These observations suggest that the brains of children with Rolandic epilepsy exhibit stronger nonstationary temporal signal fluctuations than controls.
  
  
  
  2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017;46:1728-1737.
authors.affiliation: Departments of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht, Netherlands.
authors.forename: Lalit
authors.initials: L
authors.lastname: Gupta
authors.affiliation: Departments of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht, Netherlands.|School for Mental Health & Neuroscience, Maastricht University Medical Center, Maastricht, Netherlands.
authors.forename: Jacobus F A
authors.identifier: 0000-0002-5271-8060
authors.initials: JFA
authors.lastname: Jansen
authors.affiliation: Departments of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht, Netherlands.|School for Mental Health & Neuroscience, Maastricht University Medical Center, Maastricht, Netherlands.
authors.forename: Paul A M
authors.initials: PAM
authors.lastname: Hofman
authors.affiliation: Departments of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht, Netherlands.|Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands.
authors.forename: René M H
authors.initials: RMH
authors.lastname: Besseling
authors.affiliation: Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands.|Epilepsy Center Kempenhaeghe, Heeze, Netherlands.
authors.forename: Anton J A
authors.initials: AJA
authors.lastname: de Louw
authors.affiliation: School for Mental Health & Neuroscience, Maastricht University Medical Center, Maastricht, Netherlands.|Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands.|Epilepsy Center Kempenhaeghe, Heeze, Netherlands.
authors.forename: Albert P
authors.initials: AP
authors.lastname: Aldenkamp
authors.affiliation: Departments of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht, Netherlands.|School for Mental Health & Neuroscience, Maastricht University Medical Center, Maastricht, Netherlands.
authors.forename: Walter H
authors.initials: WH
authors.lastname: Backes
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D002648:Child; D019277:Entropy; D019305:Epilepsy, Rolandic / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*
keywords: BOLD time series; Rolandic epilepsy; discrete wavelet transform; frequency structure; wavelet entropy