Spatiotemporal encoding as a robust basis for fast three-dimensional in vivo MRI

Recent studies have described some of the new opportunities that have arisen within the context of ultrafast two-dimensional imaging with the advent of spatiotemporal encoding methods. This article explores the potential of integrating these non-Fourier, single-scan, two-dimensional MRI principles, with multi-slice and phase-encoding schemes acting along a third dimension. In unison, these combinations enable the acquisition of complete three-dimensional images from volumes of interest within a 1-s timescale. A number of alternatives are explored for carrying out these very rapid three-dimensional acquisitions, including the use of two-dimensional, slice-selective, spatiotemporal encoding radiofrequency pulses, driven-equilibrium slice-selective schemes, and phase-encoded volumetric approaches. When tested under in vivo conditions, the 'hybrid' schemes combining spatiotemporal encoding with k-encoding imaging principles, proved to be superior to traditional schemes based on echo planar imaging. The resulting images were found to be less affected by field inhomogeneities and by other potential offset-derived distortions owing to a combination of factors whose origin is discussed. Further features, extensions and applications of these principles are also addressed.