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J Neurosci Methods. 2015 Feb 15;241:85-93. doi: 10.1016/j.jneumeth.2014.12.014. Epub 2014 Dec 26.

Intrinsic functional brain mapping in reconstructed 4D magnetic susceptibility (χ) data space.

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The Mind Research Network and LBERI, Albuquerque, NM 87106, United States. Electronic address:
The Mind Research Network and LBERI, Albuquerque, NM 87106, United States; University of New Mexico, ECE Department, Albuquerque, NM 87131, United States.



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.


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.


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.


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.


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.


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

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