Temporal Signal-to-Noise Changes in Combined Multislice- and In-Plane-Accelerated Echo-Planar Imaging with a 20- and 64-Channel Coil

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 wholebrain 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.

Supracategorical fear information revealed by aversively conditioning multiple categories

“…The neuroimaging experiment was carried out at the University of Regensburg, Germany using the 3T researchdedicated MR scanner (Magnetom Prisma, Siemens, Erlangen, Germany) and a 64-channel head coil. Functional images were acquired with a T2*-weighted EPI sequence (64 slices per volume, acquired with a multiband factor of 4 [18,19], field of view (FOV) = 192 × 192 mm2, isotropic voxel resolution (VR) of 2 × 2 × 2 mm3, no interslice gap, repetition time (TR) = 2000 ms, echo time (TE) = 30 ms, flip angle (FA) = 75°). Four dummy scans from the beginning of each functional run were acquired to account for signal saturation.…”

Recommendations of Choice of Head Coil and Prescan Normalize Filter Depend on Region of Interest and Task

“…Kaza et al (2011) found an improvement for the 32-channel head coil compared with the 12-channel head coil. There are only two studies investigating the differences between the 20-channel and 64-channel Siemens head coils, but not with commonly used fMRI settings, as in the current study, but regarding (t)SNR in different types of acceleration methods (Seidel et al, 2020;Sica et al, 2020). According to these studies, the 64-channel head coil showed in general less tSNR decrease, as a consequence of acceleration methods, than did the 20-channel head coil.…”

“…The overall pattern of the tSNR underlined the findings regarding the prescan normalize filter, where it was clearly visualized, that in the central parts, the tSNR was higher with the prescan normalize ON, whereas in the cortex, the prescan normalize OFF resulted in higher tSNR. Previous studies found an increase in (t)SNR with head coils with more channels, especially in multislice accelerated measurements (Seidel et al, 2020), which was not done in the current study, where only in-plane acceleration (GRAPPA = 2) was used, or in the subcortical areas (Kaza et al, 2011). In our study, however, except for the visual cortex, which is closest to the coil elements, there was no clear improvement in tSNR with respect to the 64-channel head coil.…”

“…It may depend on the sequences and their parameters; e.g., when using a multislice protocol, with different acceleration methods or different voxel sizes, the performance of the head coils might differ. Seidel et al (2020) compared both the 20-channel and 64-channel head coils with various acceleration methods and found that tSNR losses occurred more in the 20-channel head coil than in the 64-channel head coil while enhancing the acceleration factor. Summarizing the results of the current study, we could show that in general there was no large difference between the 20-channel and 64-channel head coils when performing fMRI paradigms.…”

Streamlined Magnetic Resonance Fingerprinting: Fast Whole-brain Coverage with Deep-learning Based Parameter Estimation

“…Compared to the single-band case (resolution = 1.1×1.1×1.3 mm 3 ), the reduced spatial resolution of the SMS version (1.7×1.7×1.3 mm 3 ) stems from the limitations of GRAPPA and SMS when used in combination. Such limitations are well documented (Seidel et al, 2020; Setsompop et al, 2012), preventing us from using GRAPPA > 2 when high SMS acceleration is used concurrently. Nonetheless, if we reduced the SMS factor, at the expense of longer acquisition time, we would be able to achieve the resolution of 1.1×1.1×1.3 mm 3 , although in that case, multiple iterations of SMS would be needed for whole-brain coverage.…”