Identifying Respiration-Related Aliasing Artifacts in the Rodent Resting-State fMRI.

Patricia Pais-Roldán,Klaus Scheffler,Bharat Biswal,Xin Yu

doi:10.3389/fnins.2018.00788

Abstract

Resting-state functional magnetic resonance imaging (rs-fMRI) combined with optogenetics and electrophysiological/calcium recordings in animal models is becoming a popular platform to investigate brain dynamics under specific neurological states. Physiological noise originating from the cardiac and respiration signal is the dominant interference in human rs-fMRI and extensive efforts have been made to reduce these artifacts from the human data. In animal fMRI studies, physiological noise sources including the respiratory and cardiorespiratory artifacts to the rs-fMRI signal fluctuation have typically been less investigated. In this article, we demonstrate evidence of aliasing effects into the low-frequency rs-fMRI signal fluctuation mainly due to respiration-induced B0 offsets in anesthetized rats. This aliased signal was examined by systematically altering the fMRI sampling rate, i.e., the time of repetition (TR), in free-breathing conditions and by adjusting the rate of ventilation. Anesthetized rats under ventilation showed a significantly narrower frequency bandwidth of the aliasing effect than free-breathing animals. It was found that the aliasing effect could be further reduced in ventilated animals with a muscle relaxant. This work elucidates the respiration-related aliasing effects on the rs-fMRI signal fluctuation from anesthetized rats, indicating non-negligible physiological noise needed to be taken care of in both awake and anesthetized animal rs-fMRI studies.

Highlights

Low-frequency (< 0.1 Hz) fMRI signal fluctuation (LFF) related to spontaneous brain dynamic signaling has been observed using a number of different brain imaging modalities (Biswal et al, 1995; Obrig et al, 2000)
A 3D Echo Planar Imaging (EPI)-fMRI method was used to study the potential interference between the animal respiration and the Resting-state functional magnetic resonance imaging (rs-fMRI) signal in anesthetized rats
Faced the unfeasibility of applying a muscle relaxant to these animals, it is critical to understand the implications of imaging a spontaneously breathing rodent before acquiring rs-fMRI data and, if possible, choose adequate parameters that allow an easy discrimination between neurological and artifactual signals

Summary

Introduction

Low-frequency (< 0.1 Hz) fMRI signal fluctuation (LFF) related to spontaneous brain dynamic signaling has been observed using a number of different brain imaging modalities (Biswal et al, 1995; Obrig et al, 2000). Applying a series of data analysis including correlation, coherence and independent component analysis of LFF during resting state scans has revealed distinct “restingstate” networks (RSN) that represent potential functional connectivity across regions in the brain (De Luca et al, 2005; Fox et al, 2009). Lu et al, 2012; Cabral et al, 2014; Stafford et al, 2014; Paasonen et al, 2018) This has allowed translational studies to specify the potential neuronal basis/underpins of the RSNs detected by fMRI in animal models. Animal fMRI has played a critical role in mapping the brain dynamics across multiple scales (Logothetis, 2002; Airaksinen et al, 2010; Hyder and Rothman, 2010; Mishra et al, 2011; Pan et al, 2011; Schulz et al, 2012; Yu et al, 2016; Yu, 2017; Albers et al, 2018; Wang et al, 2018). The multi-modal animal fMRI offers the possibility of studying the multi-site neural components underlying the RSNs

Methods

Results

Discussion

Conclusion