A Comparative Study For FMRI With Different TR In Small-world Brain Networks And Its Application In Normal Aging

Resting-state functional magnetic resonance imaging(R-fMRI)with shorter repetition time(TR)can acquire more temporal signals.However,little is known about the difference in the network organization of fMRI derived from varied TRs.Simultaneously,the network properties of fMRI are subject to the frequency interval,and whether the network characteristics of fMRI scanned by short TR are modulated by multi-spectrums is still unclear.Additionally,the fMRI with high temporal resolution provides a new method of investigating the changes in small-world brain networks with normal aging,which will be advantageous to the computer aided diagnosis of brain disease.The graph theory was used to analysis MRI.The images with two kinds of TR(0.5 vs.2 s)were obtained from 20 healthy young subjects,and seven small-world parameters(clustering coefficient Cp,characteristic path length Lp,local efficiency Eloc,global efficiency,Eg,?,?,?)were calculated.The single spectrum(0.01-0.1Hz)was subsequently decomposed into five equal-length multi-spectrums based on the shorter TR condition,and the same seven parameters were computed.Finally,the time series and the regional gray matter volume were separately obtained from the R-fMRI and structural MRI(sMRI),and an additional parameter(betweenness,bi)was estimated.Results presented that the R-fMRI with shorter TR,in contrast to the R-fMRI with longer TR,showed significant increases in ?,?,Cp,Eloc and Eg,as well as reductions in ? and Lp.The R-fMRI of 0.082-0.1Hz was different from that of the other four multi-spectrums,characterized by significant decline in ? and Eg,and rise in Cp,Lp and Eloc.The significant decreases of Cp and Eloc were found in the R-fMRI of old group.The value of bi in the right inferior temporal gyrus(ITG)fell significantly in the R-fMRI of the old group.In the comparison of sMRI,the old group displayed significant reductions in the values of bi in the right superior occipital gyrus(SOG),angular gyrus(ANG).In conclusion,the R-fMRI with shorter TR can strengthen the small-world topological characteristics.The small-world topological properties of the R-fMRI in 0.082-0.1Hz were relatively weaker than those in 0.01-0.082 Hz.The local properties of R-fMRI in the old group dropped slightly.The old group exhibited a decline in the abilities of the long term memory and the perception of visual space.