Magnetic resonance fast Fourier imaging

Abstract

A new method for fast magnetic resonance imaging is presented. It provides a more rapid data acquisition than two-dimensional Fourier imaging (2DFI) by a factor which may be chosen depending on the required signal-to-noise ratio of the image. In addition to the readout gradient of 2DFI, the present method employs an oscillating modulation gradient. In this way, a curved alternating trajectory in k space is sampled after each spin excitation. For a p-times accelerated data acquisition, the trajectory consists of p periods, where p is of the order of 2 to 8 for low-frequency gradient modulation but can be chosen higher if certain hardware requirements are met. Adequate sampling density in k space is obtained by scanning shifted trajectories after subsequent spin excitations. The method can be combined with volume imaging (3DFI) and multiple slice 2DFI. It was implemented on a standard Philips Gyroscan system without any hardware modifications. Results obtained for an acceleration factor p = 4 are shown.

Improved image reconstruction for partial fourier gradient‐echo echo‐planar imaging (EPI)

“…For example, the reconstructed image shown in Fig. 2e is obtained with Cuppen's partial Fourier reconstruction method (1, 5), in which the required image background phase information is measured from the full k ‐space data. The signal loss artifact shown in Fig.…”

“…and6. In our implementation, we choose Cuppen's iterative method as our partial Fourier calculation strategy (1, 5). As described in the next two paragraphs, the two reconstruction schemes in Fig.…”

“…It has been shown in recent works, that for high‐resolution functional MRI (fMRI) studies, a partial Fourier acquisition scheme (1–7) is superior to full Fourier acquisition in two ways (8, 9). First, the desired echo time (TE) value that provides the optimal BOLD sensitivity may not be achievable with a high‐resolution full Fourier echo planar imaging (EPI) scan because of the very long acquisition window of high‐resolution EPI.…”

Interleaved diffusion-weighted improved by adaptive partial-Fourier and multiband multiplexed sensitivity-encoding reconstruction

“…Fourth, the smoothed phase information and the Nyquist‐corrected EPI data from all segments are included in a mathematical framework that jointly estimates the aliasing‐free magnitude proton density maps (assumed to be consistent across multiple EPI segments) using known coil sensitivity profiles as constraints. If the DWI data are acquired with a partial‐Fourier scheme, then the missing ky lines in each Nyquist‐corrected EPI segment can be estimated from the acquired ky lines with Cuppen's iterative algorithm , which preserves the phase information, before the SENSE reconstruction in step 2. Using the MUSE algorithm, aliasing artifacts resulting from intersegment phase inconsistencies can be eliminated without relying on additional navigator echoes.…”

“…The reported MUSE implementation, however, has a few technical limitations. First, when there exist either significant motion‐induced k‐space energy displacements along the phase‐encoding direction of DWI data or pronounced local susceptibility field gradients, the conventional partial‐Fourier phase estimation procedures [e.g., Cuppen's iterative algorithm ; Homodyne reconstruction ] become inappropriate and the reconstructed partial‐Fourier MUSE images may be prone to residual artifacts. Second, as compared with single‐shot or single‐shot parallel EPI, multishot interleaved EPI has a significantly lower imaging throughput.…”