Abstract
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.
Original language | English |
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Pages (from-to) | 886-895 |
Number of pages | 10 |
Journal | Neuroimage |
Volume | 172 |
Early online date | 5 Dec 2017 |
DOIs | |
Publication status | Published - 15 May 2018 |
Keywords
- 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