Enhancement of temporal resolution and BOLD sensitivity in real-time fMRI using multi-slab echo-volumar imaging

Abstract

In this study, a new approach to high-speed fMRI using multi-slab echo-volumar imaging (EVI) is developed that minimizes geometrical image distortion and spatial blurring, and enables nonaliased sampling of physiological signal fluctuation to increase BOLD sensitivity compared to conventional echo-planar imaging (EPI). Real-time fMRI using whole brain 4-slab EVI with 286 ms temporal resolution (4 mm isotropic voxel size) and partial brain 2-slab EVI with 136 ms temporal resolution (4×4×6 mm3 voxel size) was performed on a clinical 3 Tesla MRI scanner equipped with 12-channel head coil. Four-slab EVI of visual and motor tasks significantly increased mean (visual: 96%, motor: 66%) and maximum t-score (visual: 263%, motor: 124%) and mean (visual: 59%, motor: 131%) and maximum (visual: 29%, motor: 67%) BOLD signal amplitude compared with EPI. Time domain moving average filtering (2 s width) to suppress physiological noise from cardiac and respiratory fluctuations further improved mean (visual: 196%, motor: 140%) and maximum (visual: 384%, motor: 200%) t-scores and increased extents of activation (visual: 73%, motor: 70%) compared to EPI. Similar sensitivity enhancement, which is attributed to high sampling rate at only moderately reduced temporal signal-to-noise ratio (mean: − 52%) and longer sampling of the BOLD effect in the echo-time domain compared to EPI, was measured in auditory cortex. Two-slab EVI further improved temporal resolution for measuring task-related activation and enabled mapping of five major resting state networks (RSNs) in individual subjects in 5 min scans. The bilateral sensorimotor, the default mode and the occipital RSNs were detectable in time frames as short as 75 s. In conclusion, the high sampling rate of real-time multi-slab EVI significantly improves sensitivity for studying the temporal dynamics of hemodynamic responses and for characterizing functional networks at high field strength in short measurement times.

Ultra-fast magnetic resonance encephalography of physiological brain activity – Glymphatic pulsation mechanisms?

“…Similar to Posse et al, 30 we also detected a negative cardiovascular pulse effect some 200-300 ms after the systolic R-wave in the vicinity of major cerebral arterial branches, c.f. Figure 4.…”

“…On our calibration motor task, the MREG signal increase was 3% and for visual task the signal increase was 4% on average (data not shown). 30 Figure 1. The R-peak locked Card map MREG signal change over the whole cardiac cycle is presented in Figure 3.…”

The Neural Basis of Time-Varying Resting-State Functional Connectivity

“…Window lengths for most dynamic studies that use sliding windows or temporal segmentation currently range from *30 sec to 2 min, limiting the scale of the changes which can be detected. The advent of fast imaging sequences that enable whole brain coverage in less than a second will increase the number of samples in a given time window and may improve sensitivity to short-lived changes (Moeller et al, 2010;Posse et al, 2012).…”

Three‐dimensional echo planar imaging with controlled aliasing: A sequence for high temporal resolution functional MRI

“…3D singleshot acquisitions require long echo trains resulting in compromises in the achievable echo time (TE) and spatial resolution and/or very high demands on the gradient hardware (9). Use of multislab echo volume imaging reduces the length of the echo train length and hence the strain on the gradients (12), however, it reduces the ability to use parallel imaging acceleration in the partition-encoding direction due to the reduced field of view (FOV). A more established strategy to overcome the limitations of EVI is the acquisition of the 3D volume in several shots (26)(27)(28)(29) known as 3D-EPI.…”