Functional Magnetic Resonance Imaging of the amygdala and subregions at 3 Tesla: A scoping review

Abstract

The amygdalae are a pair of small brain structures, each of which is composed of three main subregions and whose function is implicated in neuropsychiatric conditions. Functional Magnetic Resonance Imaging (fMRI) has been utilised extensively in investigation of amygdala activation and functional connectivity with most clinical research sites now utilising 3 Tesla (3T) MR systems. However, accurate imaging and analysis remains challenging not just due to the small size of the amygdala, but also its location deep in the temporal lobe. Selection of imaging parameters can significantly impact data quality with implications for the accuracy of study results and validity of conclusions. Wide variation exists in acquisition protocols with spatial resolution of some protocols suboptimal for accurate assessment of the amygdala as a whole, and for measuring activation and functional connectivity of the three main subregions, each of which contains multiple nuclei with specialised roles. The primary objective of this scoping review is to provide a comprehensive overview of 3T fMRI protocols in use to image the activation and functional connectivity of the amygdala with particular reference to spatial resolution. The secondary objective is to provide context for a discussion culminating in recommendations for a standardised protocol for imaging activation of the amygdala and its subregions. As the advantages of big data and protocol harmonisation in imaging become more apparent so, too, do the disadvantages of data heterogeneity.