Abstract: Three dimensional magnetic resonance imaging employs spiral trajectories which traverse a volume in k-space. The spiral trajectories can include interleaved planar k-space trajectories which are axially rotated as in projection-reconstruction or planar k-space trajectories which traverse parallel planar slices through the volume. The volume can be spherical, ellipsoidal, or defined by generatrices of a family of cones. The scans provide faster coverage of k-space and thus reduce total scan time.

Abstract: Disclosed is a rapid data acquisition method that applies spiral-based k-space trajectories to spectroscopic imaging. In contrast to conventional acquisition methods, this technique offers independent control over imaging time and spatial resolution. The rapid scan enables the acquisition of spectroscopic data from three spatial dimensions in the same time that conventional methods acquire a single slice. This three-dimensional acquisition delivers an order of magnitude more data than the conventional methods, with no loss in SNR. In addition to three-dimensional spectroscopic imaging, other applications of the rapid k-space scanning with spiral trajectories are described. Sophisticated acquisition methods based on multiple-quantum editing can be incorporated into spectroscopic imaging sequences without a loss in SNR. These editing methods have shown particular promise in the detection of the important lactate signal in the presence of strong, undesired lipid signals.

Abstract: A fast and robust method for correcting magnetic resonance image distortion due to field inhomogeneity is applied to spiral k-space scanning. The method includes acquiring a local field map, finding the best fit to a linear map, and using the linear field map to deblur the image distortions due to local frequency variations. The linear field map is determined using a maximum likelihood estimator with weights proportional to the pixel intensity. The method requires little additional computation and is robust in low signal regions and near abrupt field changes. The application of this method is illustrated in conjunction with a multi-slice, T2-weighted, breath-held spiral scan of the liver.

Abstract: Real-time spatially localized velocity distribution is measured using magnetic resonance techniques by first exciting a region of interest using an RF excitation pulse simultaneously with gradient pulses along two orthogonal axes. A cyclical read-out gradient is then applied along a read-out axis and a magnetic resonance signal is continuously sampled while the read-out gradient is applied. The excitation and read-out is repeated at time intervals to obtain time varying spatially localized velocities within the region of interest.