title: Adaptive independent vector analysis for multi-subject complex-valued fMRI data.
abstract: BACKGROUND
  Complex-valued fMRI data can provide additional insights beyond magnitude-only data. However, independent vector analysis (IVA), which has exhibited great potential for group analysis of magnitude-only fMRI data, has rarely been applied to complex-valued fMRI data. The main challenges in this application include the extremely noisy nature and large variability of the source component vector (SCV) distribution.
  
  
  METHODS
  To address these challenges, we propose an adaptive fixed-point IVA algorithm for analyzing multiple-subject complex-valued fMRI data. We exploited a multivariate generalized Gaussian distribution (MGGD)- based nonlinear function to match varying SCV distributions in which the MGGD shape parameter was estimated using maximum likelihood estimation. To achieve our de-noising goal, we updated the MGGD-based nonlinearity in the dominant SCV subspace, and employed a post-IVA de-noising strategy based on phase information in the IVA estimates. We also incorporated the pseudo-covariance matrix of fMRI data into the algorithm to emphasize the noncircularity of complex-valued fMRI sources.
  
  
  RESULTS
  Results from simulated and experimental fMRI data demonstrated the efficacy of our method.
  
  
  METHODS
  Our approach exhibited significant improvements over typical complex-valued IVA algorithms, especially during higher noise levels and larger spatial and temporal changes. As expected, the proposed complex-valued IVA algorithm detected more contiguous and reasonable activations than the magnitude-only method for task-related (393%) and default mode (301%) spatial maps.
  
  
  CONCLUSIONS
  The proposed approach is suitable for decomposing multi-subject complex-valued fMRI data, and has great potential for capturing additional subject variability.
authors.affiliation: School of Information and Communication Engineering, Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024, China.
authors.forename: Li-Dan
authors.initials: LD
authors.lastname: Kuang
authors.affiliation: School of Information and Communication Engineering, Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024, China. Electronic address: qhlin@dlut.edu.cn.
authors.forename: Qiu-Hua
authors.initials: QH
authors.lastname: Lin
authors.affiliation: School of Information and Communication Engineering, Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024, China.
authors.forename: Xiao-Feng
authors.initials: XF
authors.lastname: Gong
authors.affiliation: Department of Biomedical Engineering, Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024, China; Department of Mathematical Information Technology, University of Jyvaskyla, Finland.
authors.forename: Fengyu
authors.initials: F
authors.lastname: Cong
authors.affiliation: The Mind Research Network, Albuquerque, NM 87106, USA; Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM 87131, USA.
authors.forename: Vince D
authors.initials: VD
authors.lastname: Calhoun
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001307:Auditory Perception / Q000502:physiology; D001921:Brain / Q000000981:diagnostic imaging / Q000502:physiology; D001931:Brain Mapping / Q000379:methods*; D003198:Computer Simulation; D005385:Fingers / Q000502:physiology; D006801:Humans; D016013:Likelihood Functions; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008959:Models, Neurological; D009043:Motor Activity / Q000502:physiology; D015999:Multivariate Analysis; D017711:Nonlinear Dynamics; D012146:Rest
keywords: Complex-valued fMRI data; Independent vector analysis (IVA); MGGD; Noncircularity; Post-IVA phase de-noising; Shape parameter; Subspace de-noising