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,

Timing delays between data acquisition and gradient transmission result in image degradation. This is especially true in spiral MRI, where delays can alter data in a nonuniform manner, generating significant artifact in the reconstructed data. The many methods that exist to mitigate these delays or measure the k-space coordinates require long measurement times, complicated analysis, specialized phantoms or hardware, or significant changes to the sequence of interest. A fast and simple method is proposed to measure delays on each gradient channel. It requires only minimal modification to an existing spiral sequence and can be used to measure independent delays on three gradient channels and any scan subject within six sequence repetition times. Accurate reconstruction of MRI data requires knowledge of the k-space sample locations. Deviations from the theoretical gradient waveforms can be caused by eddy currents, gradient amplifier nonlinearities, and other system imperfections. These deviations take the form of gradient timing delays and amplitude distortions that result in altered sample locations in k-space, producing artifacts in the reconstructed images. In spiral trajectories, these artifacts can be mistaken for aliasing, loss of resolution, poor signalto noise-ratio, or off-resonance blurring, thus making the source of the artifacts difficult to discern.Modern MRI scanners mitigate eddy currents through the use of gradient coil shielding and gradient waveform preemphasis. Sequences that place large gradient slew-rate and amplitude demands on the hardware can induce eddy currents, despite gradient coil shielding. Gradient waveform pre-emphasis provides an additional level of eddy current compensation but can only be optimized for a limited range of sequences. A number of techniques have been employed to compensate for the remaining deviations from the expected k-space coordinates.Several strategies seek to measure the actual gradient waveform for correct reconstruction or improved gradient pre-emphasis. Spielman and Pauly (1) directly measured the current on each gradient channel. Errors from the gradient amplifier were directly measured, but eddy currents were assumed to be negligible. Onodera et al. (2) proposed

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Perfusion-based changes in MR signal intensity can occur in response to the introduction of exogenous contrast agents and endogenous tissue properties (e.g. blood oxygenation). MR measurements aimed at capturing these changes often implement single-shot echo planar imaging (ssEPI). In recent years ssEPI readouts have been combined with parallel imaging (PI) to allow fast dynamic multi-slice imaging as well as the incorporation of multiple echoes. A multiple spin- and gradient-echo (SAGE) EPI acquisition has recently been developed to allow measurement of transverse relaxation rate (R2 and R2*) changes in dynamic susceptibility contrast (DSC)-MRI experiments in the brain. With SAGE EPI, the use of PI can influence image quality, temporal resolution, and achievable echo times. The effect of PI on dynamic SAGE measurements, however, has not been evaluated. In this work, a SAGE EPI acquisition utilizing SENSE PI and partial Fourier (PF) acceleration was developed and evaluated. Voxel-wise measures of R2 and R2* in healthy brain were compared using SAGE EPI and conventional non-EPI multiple echo acquisitions with varying SENSE and PF acceleration. A conservative SENSE factor of 2 with PF factor of 0.73 was found to provide accurate measures of R2 and R2* in white (WM) (rR2 = [0.55–0.79], rR2* = [0.47–0.71]) and gray (GM) matter (rR2 = [0.26–0.59], rR2* = [0.39–0.74]) across subjects. The combined use of SENSE and PF allowed the first dynamic SAGE EPI measurements in muscle, with a SENSE factor of 3 and PF factor of 0.6 providing reliable relaxation rate estimates when compared to multi-echo methods. Application of the optimized SAGE protocol in DSC-MRI of high-grade glioma patients provided T1 leakage-corrected estimates of CBV and CBF as well as mean vessel diameter (mVD) and simultaneous measures of DCE-MRI parameters Ktrans and ve. Likewise, application of SAGE in a muscle reperfusion model allowed dynamic measures of R2′, a parameter that has been shown to correlate with muscle oxy-hemoglobin saturation.