Reducing sensitivity losses due to respiration and motion in accelerated echo planar imaging by reordering the autocalibration data acquisition

Abstract

Purpose To reduce the sensitivity of echo-planar imaging (EPI) Auto-Calibration Signal (ACS) data to patient respiration and motion in order to improve the image quality and temporal Signal-to-Noise Ratio (tSNR) of accelerated EPI time-series data. Methods ACS data for accelerated EPI are generally acquired using segmented, multi-shot EPI to distortion-match the ACS and time-series data. The ACS data are therefore typically collected over multiple TR periods, leading to increased vulnerability to motion and dynamic B0 changes. The Fast Low-angle Excitation Echo-planar Technique (FLEET) is adopted to reorder the ACS segments so that segments within any given slice are acquired consecutively in time, thereby acquiring ACS data for each slice as rapidly as possible. Results Subject breath-hold and motion phantom experiments demonstrate that artifacts in the ACS data reduce tSNR and produce tSNR discontinuities across slices in the accelerated EPI time-series data. Accelerated EPI data reconstructed using FLEET-ACS exhibit improved tSNR and increased tSNR continuity across slices. Additionally, image quality is improved dramatically when bulk motion occurs during the ACS acquisition. Conclusion FLEET-ACS provides reduced respiration and motion sensitivity in accelerated EPI, which yields higher tSNR and image quality. Benefits are demonstrated in both conventional-resolution 3T and high-resolution 7T EPI time-series data.

Interdigitated Color- and Disparity-Selective Columns within Human Visual Cortical Areas V2 and V3

“…Two RDSs (each either red or green) were overlaid and fused within all experiment blocks. In one condition, stimuli formed a stereoscopic percept of a regular array of cuboids that varied sinusoidally in depth (Ϯ0.22°), with independent phase, similar to a stimulus described earlier (Tsao et al, 2003;Neri et al, 2004;Bridge and Parker, 2007;Minini et al, 2010). In the control condition, the fused percept formed a frontoparallel plane intersecting the fixation target (i.e., zero depth at that point).…”

“…Voxel dimensions were nominally 1.0 mm, isotropic, except as noted below. Single-shot gradient-echo EPI was used to acquire functional images with the following protocol parameter values: TR, 3000 ms; TE, 28 ms; flip angle, 78°; matrix, 192 ϫ 192; band width (BW), 1184 Hz/pix; echospacing, 1 ms; 7/8 phase partial Fourier; FOV, 192 ϫ 192 mm; 44 oblique-coronal slices; and acceleration factor r ϭ 4 with GRAPPA reconstruction and FLEET-ACS data (Polimeni et al, 2015) with 10°flip angle. The field of view included occipital cortical areas V1, V2, V3, and the posterior parts of V4v and V4d.…”

“…We tried to minimize the latter impact of blurring due to the large vessels by differential stimulation paradigms (also see Yacoub et al, 2008), and also by sampling far from the pial surface (Polimeni et al, 2010; also see below). With regard to the former (pulsatility artifacts), previous studies (Enzmann and Pelc, 1992; Poncelet et al, 1992) have estimated this effect to produce ϳ90 m of tissue displacement in the occipital Figure 5.…”

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

“…Care was taken to ensure that the segmented EPI trains corresponding to the primary phase-encoding lines were acquired in the inner loop while the secondary phase-encoding loop was kept as the outer loop. Note that, as opposed to multiband 2D-EPI, in 3D EPI, the steady state is not altered by such an ordering loop, but the same advantages can be found: reduction of reconstruction artifacts associated with large physiological state variations in neighboring k-space data of the ACS data (40). The undersampled (accelerated) data were then acquired using sampling patterns mentioned in the theory section.…”

Two‐dimensional‐NGC‐SENSE‐GRAPPA for fast, ghosting‐robust reconstruction of in‐plane and slice‐accelerated blipped‐CAIPI echo planar imaging

“…The importance of good reference data is a topic of active investigation, and specifically the FLEET‐like ACS data acquisitions could offer a good solution 22. These allow distortion‐matched ACS lines to be acquired using a segmented approach while alleviating the effects of intersegment physiological fluctuations that would otherwise corrupt the ACS data.…”