Temporal signal-to-noise changes in combined multiband- and slice-accelerated echo-planar imaging with a 20- and 64-channel coil

Abstract

Echo planar imaging (EPI) is the most common method of functional magnetic resonance imaging for acquiring the blood oxygenation level-dependent (BOLD) contrast. One of the primary benefits of using EPI is that an entire volume of the brain can be acquired on the order of two seconds. However, this speed benefit comes with a cost. Because imaging protocols are limited by hardware (e.g., fast gradient switching), researchers are forced to 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., slice (S) acceleration), while more recent protocols allow for multiple slices to be acquired simultaneously (i.e., multiband (MB) acceleration). However, applying such acceleration methods can lead to a reduction in the temporal signal-to-noise ratio (tSNR), which is a critical measure of the stability of the signal over time. Here we show, in five healthy subjects, using a 20-and 64-channel receiver coil, that enabling S-acceleration consistently yielded, as expected, a substantial decrease in tSNR, regardless of the receiver coil employed, whereas tSNR decrease resulting from MB acceleration was less pronounced. Specifically, with the 20-channel coil, tSNR of upto 4-fold MB-acceleration is comparable to that of no acceleration, while up to 6-fold MB-acceleration with the 64-channel coil yields comparable tSNR to that of no acceleration. Moreover, observed tSNR losses tended to be localized to temporal, insular, and medial brain regions and were more noticeable in the 20than in the 64-channel coil. Conversely, with the 64-channel coil, the tSNR in lateral frontoparietal regions remained relatively stable with increasing MB factors.Such methodological explorations can inform researchers and clinicians as to how they can optimize imaging protocols depending on the available hardware and the brain regions they want to investigate.

Inhalation-modulated detection of olfactory BOLD responses in the human brain

“…All imaging data were acquired on a 3T Siemens Prisma (Siemens Healthcare, Erlangen, Germany) using a 64-channel receiver head coil (Siemens Healthcare) and multiband sequences (epfid2d1_64) provided by the Center for Magnetic Resonance Research (CMRR, Minneapolis, Minnesota, USA). Twelve functional sequences of 104 volumes (total duration 12 * 3 min:28 s) covering the whole brain with 88 slices of 2 × 2 × 2 mm isotropic voxels, repetition time (TR) = 2,000 ms, echo time (TE) = 30 ms, flip angle (FA) = 75 • , excitation pulse duration = 9 ms, echo spacing = 0.58 ms, bandwidth = 2,368 Hz/pixel; acquisition matrix (AM) = 96 × 96; field of view (FoV) = 192 × 192 mm; partial Fourier = 7/8 and a multiband acceleration factor of 4 in order to maximize the temporal signal-to-noise ratio (Seidel et al, 2020).…”