Effect of Phase-Encoding Direction on Gender Differences: A Resting-State Functional Magnetic Resonance Imaging Study

Abstract

AimNeuroimaging studies have highlighted gender differences in brain functions, but conclusions are not well established. Few studies paid attention to the influence of phase-encoding (PE) direction in echo-planar imaging on gender differences, which is a commonly used technique in functional magnetic resonance imaging (fMRI). A disadvantage of echo-planar images is the geometrical distortion and signal loss due to large susceptibility effects along the PE direction. The present research aimed to clarify how PE direction can affect the outcome of a specific research on gender differences.MethodsWe collected resting-state fMRI using anterior to posterior (AP) and posterior to anterior (PA) directions from 113 healthy participants. We calculated several commonly used indices for spontaneous brain activity including amplitude of low frequency fluctuations (ALFF), fractional ALFF (fALFF), regional homogeneity (ReHo), degree centrality (DC), and functional connectivity (FC) of posterior cingulate cortex for each session, and performed three group comparisons: (i) AP versus PA; (ii) male versus female; (iii) interaction between gender and PE direction.ResultsThe estimated indices differed substantially between the two PE directions, and the regions that exhibited differences were roughly similar for all the indices. In addition, we found that multiple brain regions showed gender differences in these estimated indices. Further, we observed an interaction effect between gender and PE direction in the bilateral middle frontal gyrus, right precentral gyrus, right postcentral gyrus, right lingual gyrus, and bilateral cerebellum posterior lobe.ConclusionThese apparent findings revealed that PE direction can partially influence gender differences in spontaneous brain activity of resting-state fMRI. Therefore, future studies should document the adopted PE direction and appropriate selection of PE direction will be important in future resting-state fMRI studies.

Effects of phase encoding direction on test-retest reliability of human functional connectome

“…Statistically, regions consistently influenced by PED in both atlases were primarily the cingulate cortex, temporal cortex, sensorimotor area, and visual area. This is similar to results in previous studies that both functional connectivity strength and amplitude of low-frequency fluctuation (ALFF) in these regions are strongly affected by PED ( Mori et al, 2018 ; Wang et al, 2021 ). Notably, these regions are not only along the PE axis during imaging acquisition but also close to air/tissue interface, which possibly suffer magnetic susceptibility induced image distortion and propagated flow or motion artifacts ( De Panfilis and Schwarzbauer, 2005 ; Weiskopf et al, 2006 ).…”

“…This raises concern as whether PED would have significant effects on test-retest reliability of the derived connectomic measures. Notably, recent studies have demonstrated significant PED-related effects on the connectivity outcome in comparison of patients with schizophrenia and healthy controls ( Mori et al, 2018 ) as well as contrasting males and females ( Wang et al, 2021 ), further strengthening the possibility of such concern.…”

“…Different PEDs are known to have different impacts on susceptibility-induced distortion and signal loss in the brain, which may in turn influence image quality and the reliability of functional connectome constructed from these images. Specifically, previous studies have shown that AP scans are commonly associated with greater signal loss in the orbitofrontal cortex, anterior cingulate cortex (ACC), and temporal lobe ( Mori et al, 2018 ; Wang et al, 2021 ; Weiskopf et al, 2006 ; Weiskopf et al, 2007 ). Less consistent findings are reported for the PA scans, which may relate to worse signals in the frontal pole, striatum, and cerebellum ( Mori et al, 2018 ; Wang et al, 2021 ).…”

“…Specifically, previous studies have shown that AP scans are commonly associated with greater signal loss in the orbitofrontal cortex, anterior cingulate cortex (ACC), and temporal lobe ( Mori et al, 2018 ; Wang et al, 2021 ; Weiskopf et al, 2006 ; Weiskopf et al, 2007 ). Less consistent findings are reported for the PA scans, which may relate to worse signals in the frontal pole, striatum, and cerebellum ( Mori et al, 2018 ; Wang et al, 2021 ). Although field maps have increasingly been collected and used with the aim of correcting for PED-related distortion, the efficacy of such corrections has not been fully investigated.…”

Effects of phase encoding direction on test-retest reliability of human functional connectome

“…Statistically, regions that were consistently influenced by PED in both atlases were the ACC and temporal cortex. This is remarkably similar to results in previous studies that both functional connectivity strength and amplitude of low-frequency fluctuation (ALFF) in these regions are strongly affected by PED (Mori et al, 2018; Wang et al, 2021). Notably, these regions are not only along the PE axis during imaging acquisition but also close to air/tissue interface, which possibly suffer magnetic susceptibility induced image distortion and propagated flow or motion artifacts (De Panfilis and Schwarzbauer, 2005; Weiskopf et al, 2006).…”