Abstract
The aural cavity magnetic susceptibility artifact leads to significant echo planar imaging (EPI) signal dropout in rat deep brain that limits acquisition of functional connectivity fcMRI data. In this study, we provide a method that recovers much of the EPI signal in deep brain. Needle puncture introduction of a liquid-phase fluorocarbon into the middle ear allows acquisition of rat fcMRI data without signal dropout. We demonstrate that with seeds chosen from previously unavailable areas, including the amygdala and the insular cortex, we are able to acquire large scale networks, including the limbic system. This tool allows EPI-based neuroscience and pharmaceutical research in rat brain using fcMRI that was previously not feasible.
Highlights
Resting-state functional connectivity MRI has been extensively studied using echo planar imaging (EPI) based methods [1]
It is clear that the EPI signals in the insular cortex and the amygdala were restored on the left side of brain
Fomblin Y was filled into both external ears of the rat, EPI signal was only restored in the left hemisphere, which shows that the air pocket in the middle ear is the major source of the magnetic susceptibility effect in the deep brain area
Summary
Resting-state functional connectivity MRI (fcMRI) has been extensively studied using echo planar imaging (EPI) based methods [1]. Functional networks in humans [1,2,3] have been discovered that involve both long range and local connectivity. Because of the anatomical and structural characteristics of animals in the aural region, especially rats, deep brain structure coverage in fcMRI remains deficient. EPI signal dropout is significant in the insular cortex, amygdala, and the hypothalamus. It has been suggested that EPI signal dropout is a result of magnetic susceptibility of air in the ear canal of the rat. Only a small portion of these brain structures is available for fcMRI studies [4,5,6,7,8,9]
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