title: Intrinsic functional brain mapping in reconstructed 4D magnetic susceptibility (χ) data space.
abstract: BACKGROUND
  By solving an inverse problem of T2*-weighted magnetic resonance imaging for a dynamic fMRI study, we reconstruct a 4D magnetic susceptibility source (χ) data space for intrinsic functional mapping.
  
  
  METHODS
  A 4D phase dataset is calculated from a 4D complex fMRI dataset. The background field and phase wrapping effect are removed by a Laplacian technique. A 3D χ source map is reconstructed from a 3D phase image by a computed inverse MRI (CIMRI) scheme. A 4D χ data space is reconstructed by repeating the 3D χ source reconstruction for each time point. A functional map is calculated by a temporal correlation between voxel signals in the 4D χ space and the timecourse of the task paradigm.
  
  
  RESULTS
  With a finger-tapping experiment, we obtain two 3D functional mappings in the 4D magnitude data space and in the reconstructed 4D χ data space. We find that the χ-based functional mapping reveals co-occurrence of bidirectional responses in a 3D activation map that is different from the conventional magnitude-based mapping.
  
  
  METHODS
  The χ-based functional mapping can also be achieved by a 3D deconvolution of a phase activation map. Based on a subject experimental comparison, we show that the 4D χ tomography method could produce a similar χ activation map as obtained by the 3D deconvolution method.
  
  
  CONCLUSIONS
  By removing the dipole effect and other fMRI technological contaminations, 4D χ tomography provides a 4D χ data space that allows a more direct and truthful functional mapping of a brain activity.
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, ECE Department, Albuquerque, NM 87131, United States.
authors.forename: Vince
authors.initials: V
authors.lastname: Calhoun
mesh_terms: D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009068:Movement / Q000502:physiology*
keywords: 4D magnetic susceptibility (χ) tomography; Blood oxygenation level-dependent functional magnetic resonance imaging (BOLD fMRI); Dipole inversion; Intrinsic functional brain mapping; T2* imaging; T2* magnitude and phase images