Abstract
Echo-planar imaging (EPI) is the most common method of functional MRI for acquiring the blood oxygenation level-dependent (BOLD) contrast, allowing the acquisition of an entire brain volume within seconds. However, because imaging protocols are limited by hardware (e.g., fast gradient switching), researchers must compromise between spatial resolution, temporal resolution, or whole-brain coverage. Earlier attempts to circumvent this problem included developing protocols in which slices of a volume were acquired faster (i.e., in-plane acceleration (S)) or simultaneously (i.e., multislice acceleration (M)). However, applying acceleration methods can lead to a reduction in the temporal signal-to-noise ratio (tSNR): a critical measure of signal stability over time. Using a 20- and 64-channel receiver coil, we show that enabling S-acceleration consistently yielded a substantial decrease in tSNR, regardless of the receiver coil, whereas M-acceleration yielded less pronounced tSNR decrease. Moreover, tSNR losses tended to occur in temporal, insular, and medial brain regions and were more noticeable with the 20-channel coil, while with the 64-channel coil, the tSNR in lateral frontoparietal regions remained relatively stable up to six-fold M-acceleration producing comparable tSNR to that of no acceleration. Such methodological explorations can guide researchers and clinicians in optimizing imaging protocols depending on the brain regions under investigation.
Highlights
One of the primary benefits of MRI in neuroscience research is the high spatial resolution attainable when investigating the whole brain, which, interacts with lower temporal resolution, whole-brain coverage, and signal-to-noise ratio (SNR)
This study investigated changes in tSNR resulting from applying acceleration methods to the acquisition of functional MRI data
We aimed to probe which brain regions were most susceptible to tSNR loss stemming from in-plane-acceleration ( GRAPPA7), multislice-acceleration[14], and a combination thereof, when other scanning parameters were held constant, and whether the type of receiver coil played a role underlying decreases in tSNR
Summary
One of the primary benefits of MRI in neuroscience research is the high spatial resolution attainable when investigating the whole brain, which, interacts with lower temporal resolution, whole-brain coverage, and signal-to-noise ratio (SNR). Multiple advances in image acquisition protocols and image reconstruction algorithms have worked toward providing both increased spatial and temporal resolution Some of these approaches, such as partial Fourier acquisition[6] and parallel imaging, e.g. the GeneRalized Autocalibrating Partial Parallel Acquisition (GRAPPA) algorithm[7] (see SENSE8 and SMASH9), reduce the acquisition time of single slices and are known as in-plane-acceleration methods (hereinafter referred to as S). There have been no systematic investigations into (1) the question of where in the brain M- and S-acceleration (and their combinations) most prominently affect tSNR when other scanning parameters are held constant and (2) whether the type of receiver coil interacts with acceleration methods with respect to tSNR changes, as well These outstanding concerns are critical to cognitive neuroscientists and clinical researchers who may have region-specific hypotheses to investigate using otherwise standard hardware setups. Such results can inform researchers regarding the feasibility of different combinations of M- and S-acceleration depending on the experimental demands and the brain regions to be investigated
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