title: Task-evoked brain functional magnetic susceptibility mapping by independent component analysis (χICA).
abstract: BACKGROUND
  Conventionally, independent component analysis (ICA) is performed on an fMRI magnitude dataset to analyze brain functional mapping (AICA). By solving the inverse problem of fMRI, we can reconstruct the brain magnetic susceptibility (χ) functional states. Upon the reconstructed χ dataspace, we propose an ICA-based brain functional χ mapping method (χICA) to extract task-evoked brain functional map.
  
  
  METHODS
  A complex division algorithm is applied to a timeseries of fMRI phase images to extract temporal phase changes (relative to an OFF-state snapshot). A computed inverse MRI (CIMRI) model is used to reconstruct a 4D brain χ response dataset. χICA is implemented by applying a spatial InfoMax ICA algorithm to the reconstructed 4D χ dataspace.
  
  
  RESULTS
  With finger-tapping experiments on a 7T system, the χICA-extracted χ-depicted functional map is similar to the SPM-inferred functional χ map by a spatial correlation of 0.67 ± 0.05. In comparison, the AICA-extracted magnitude-depicted map is correlated with the SPM magnitude map by 0.81 ± 0.05. The understanding of the inferiority of χICA to AICA for task-evoked functional map is an ongoing research topic.
  
  
  METHODS
  For task-evoked brain functional mapping, we compare the data-driven ICA method with the task-correlated SPM method. In particular, we compare χICA with AICA for extracting task-correlated timecourses and functional maps.
  
  
  CONCLUSIONS
  χICA can extract a χ-depicted task-evoked brain functional map from a reconstructed χ dataspace without the knowledge about brain hemodynamic responses. The χICA-extracted brain functional χ map reveals a bidirectional BOLD response pattern that is unavailable (or different) from AICA.
authors.affiliation: The Mind Research Network and LBERI, Albuquerque, NM 87106, United States. Electronic address: zchen@mrn.org.
authors.forename: Zikuan
authors.initials: Z
authors.lastname: Chen
authors.affiliation: The Mind Research Network and LBERI, Albuquerque, NM 87106, United States; University of New Mexico, Department of Electrical and Computer Engineering, Albuquerque, NM 87131, United States.
authors.forename: Vince D
authors.initials: VD
authors.lastname: Calhoun
mesh_terms: D000465:Algorithms; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D002560:Cerebrovascular Circulation / Q000502:physiology; D066264:Datasets as Topic; D005385:Fingers / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009043:Motor Activity / Q000502:physiology; D010100:Oxygen / Q000097:blood; D015203:Reproducibility of Results
chemical_list: D010100:Oxygen
keywords: Bidirectional BOLD responses; Computed inverse MRI (CIMRI); Function-structure colocalization; Independent component analysis (ICA); Model timecourse; Spatiotemporal separation; Task-evoked brain functional mapping