A new design and rationale for 3D orthogonally oversampled k‐space trajectories

Abstract

A novel center-out 3D trajectory for sampling magnetic resonance data is presented. The trajectory set is based on a single Fermat spiral waveform, which is substantially undersampled in the center of k-space. Multiple trajectories are combined in a ''stacked cone'' configuration to give very uniform sampling throughout a ''hub,'' which is very efficient in terms of gradient performance and uniform trajectory spacing. The fermat looped, orthogonally encoded trajectories (FLORET) design produces less gradient-efficient trajectories near the poles, so multiple orthogonal hub designs are shown. These multihub designs oversample k-space twice with orthogonal trajectories, which gives unique properties but also doubles the minimum scan time for critical sampling of k-space. The trajectory is shown to be much more efficient than the conventional stack of cones trajectory, and has nearly the same signal-to-noise ratio efficiency (but twice the minimum scan time) as a stack of spirals trajectory. As a center-out trajectory, it provides a shorter minimum echo time than stack of spirals, and its spherical k-space coverage can dramatically reduce Gibbs ringing. Magn Reson Med 66:1303-1311,

Sodium MRI: Methods and applications

“…This method can be further improved with respect to signal-to-noise ratio (SNR) and time efficiency by modifying the density of acquisition points along the projections and also by twisting the radial projection in the outer k -space in an optimal manner in order to fill k -space more homogeneously and thus to improve the point spread function of the acquisition method. This is done in sequences such as the density adapted radial sequence [113], the twisted projection imaging (TPI) and its variations [29,114,115], the 3D cones [116] and in the FLORET sequences [117]. Examples of k -space trajectories from 3D radial and TPI sequences are shown in Fig.…”

A nested phosphorus and proton coil array for brain magnetic resonance imaging and spectroscopy

“…The number of Gaussian pulses defined t sat in each experiment (eight experiments total, t sat min = 0, and t sat max = 6.8s). 3) Images of single metabolites (PCr and γ-ATP) were acquired using a spectrally selective 3D non-Cartesian fermat looped, orthogonally encoded trajectories (FLORET) pulse sequence with 1.4 cm isotropic resolution (Madelin et al, 2014; Pipe et al, 2011). …”

Sodium MR Imaging of Articular Cartilage Pathologies

“…Twisted projection imaging (TPI) is another approach for sodium MR imaging with efficient k-space sampling and improved SNR [22, 23]. Many other techniques, such as 3D cones [24], acquisition-weighted stack of spirals [25] and FLORET [26], were inspired by TPI. The data acquired with non-Cartesian UTE sequences are reconstructed by using regridding reconstruction [27–29] or nonuniform fast Fourier transform algorithms [30, 31].…”