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Using multi-echo simultaneous multi-slice (SMS) EPI to improve functional MRI of the subcortical nuclei of the basal ganglia at ultra-high field (7T)

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The nuclei of the basal ganglia pose a special problem for functional MRI, especially at ultra-high field, because T2* variations between different regions result in suboptimal BOLD sensitivity when using gradient-echo echo-planar imaging (EPI). Specifically, the iron-rich lentiform nucleus of the basal ganglia, including the putamen and globus pallidus, suffers from substantial signal loss when imaging is performed using conventional single-echo EPI with echo times (TE) optimized for the cortex. Multi-echo EPI acquires several echoes at different echo times for every imaging slice, allowing images to be reconstructed with a weighting of echo times that is optimized individually for each voxel according to the underlying tissue or T2* properties. Here we show that multi-echo simultaneous multi-slice (SMS) EPI can improve functional activation of iron-rich subcortical regions while maintaining sensitivity within cortical areas. Functional imaging during a motor task known to elicit strong activations in the cortex and the subcortex (basal ganglia) was performed to compare the performance of multi-echo SMS EPI to single-echo SMS EPI. Notably within both the caudate nucleus and putamen of the basal ganglia, multi-echo SMS EPI yielded higher tSNR (an average 84% increase) and CNR (an average 58% increase), an approximate 3-fold increase in supra-threshold voxels, and higher t-values (an average 39% increase). The degree of improvement in the group level t-statistics was negatively correlated to the underlying T2* of the voxels, such that the shorter the T2*, as in the iron-rich nuclei of the basal ganglia, the higher the improvement of t-values in the activated region.

    Research areas

  • Journal Article, TRANSVERSE RELAXATION RATES, SINGLE-SHOT, HUMAN BRAIN, Motor, Susceptibility artifacts, 3 T, IRON CONTENT, CORTEX, SEGMENTED EPI, Signal loss, Echo time, PHYSIOLOGICAL NOISE, Functional MRI, BOLD-CONTRAST SENSITIVITY, Simultaneous multi-slice, Multi-echo, TASK FMRI, EPI, Echo-Planar Imaging/methods, Humans, Magnetic Resonance Imaging/methods, Male, Young Adult, Adult, Female, Brain Mapping/methods, Basal Ganglia/diagnostic imaging
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Original languageEnglish
Pages (from-to)886-895
Number of pages10
Early online date5 Dec 2017
Publication statusPublished - 15 May 2018