title: Fast computation of voxel-level brain connectivity maps from resting-state functional MRI using l₁-norm as approximation of Pearson's temporal correlation: proof-of-concept and example vector hardware implementation.
abstract: An outstanding issue in graph-based analysis of resting-state functional MRI is choice of network nodes. Individual consideration of entire brain voxels may represent a less biased approach than parcellating the cortex according to pre-determined atlases, but entails establishing connectedness for 1(9)-1(11) links, with often prohibitive computational cost. Using a representative Human Connectome Project dataset, we show that, following appropriate time-series normalization, it may be possible to accelerate connectivity determination replacing Pearson correlation with l1-norm. Even though the adjacency matrices derived from correlation coefficients and l1-norms are not identical, their similarity is high. Further, we describe and provide in full an example vector hardware implementation of l1-norm on an array of 4096 zero instruction-set processors. Calculation times <1000 s are attainable, removing the major deterrent to voxel-based resting-sate network mapping and revealing fine-grained node degree heterogeneity. L1-norm should be given consideration as a substitute for correlation in very high-density resting-state functional connectivity analyses.
authors.affiliation: Scientific Department, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy; MR-Lab, Center for Mind/Brain Science, University of Trento, Italy. Electronic address: lminati@ieee.org.
authors.forename: Ludovico
authors.initials: L
authors.lastname: Minati
authors.affiliation: MR-Lab, Center for Mind/Brain Science, University of Trento, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Zacà
authors.affiliation: Neuroradiology Unit, Fondazione IRCCS IstitutoNeurologico Carlo Besta, Milan, Italy.
authors.forename: Ludovico
authors.initials: L
authors.lastname: D'Incerti
authors.affiliation: MR-Lab, Center for Mind/Brain Science, University of Trento, Italy.
authors.forename: Jorge
authors.initials: J
authors.lastname: Jovicich
mesh_terms: D001921:Brain / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D063132:Connectome / Q000295:instrumentation / Q000379:methods; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009434:Neural Pathways / Q000502:physiology; D010100:Oxygen / Q000097:blood; D012146:Rest; D013995:Time
chemical_list: D010100:Oxygen
keywords: Brain networks; Connectome; Correlation coefficient; Parallel processing; Resting-state functional MRI (rs-fMRI); Vector hardware co-processor; l(1)-Norm