Interleaved multishot imaging by spatiotemporal encoding: A fast, self-referenced method for high-definition diffusion and functional MRI

Abstract

We have developed an interleaved SPEN approach for the acquisition of high-definition images that promises a wider range of functional and diffusion MRI applications even in challenging environments.

Robust diffusion tensor imaging by spatiotemporal encoding: Principles and in vivo demonstrations

“…RF pulse manipulations include a chirped‐90° pulse followed by a single‐slice refocusing 180° pulse ( a ), a chirped‐180° multislice approach ( b ), and a slice‐selective 2D pulse imparting a 90° chirped‐like evolution ( c ). Diffusion‐sensitizing gradients (indicated by stepped gray gradients) are symmetrically located on both sides of a central refocusing pulse in (a) and (c), and placed in a pre‐encoding T a /2 delay required by (b) to reach full‐refocusing conditions . The RF/ADC line displays the pulses and signal acquisitions; G e , encoding gradient; G d , diffusion‐weighting gradients; G ss , slice‐selective gradient; G pr , purge gradients; G cr , crusher gradients; G a , acquisition gradients; K shot , step gradient for interleaved multishot mode; T e , encoding time; T a , acquisition time; N pe , number of loops encoding the low‐bandwidth (SPEN) dimensions; N sl , number of slices; N shot , number of shots, when implemented in a segmented, reference‐less acquisition mode .…”

“…This leads to SPEN images that are nearly T 2 * ‐free. The potential of various SPEN imaging forms in both single/interleaved‐shot and single/parallel‐receive acquisition modes , has been demonstrated in several applications including BOLD and isotropic diffusivity studies. The present study describes the use of SPEN within a DTI framework.…”

A regularized reconstruction pipeline for high‐definition diffusion MRI in challenging regions incorporating a per‐shot image correction

“…SPEN's FOV is also defined before the acquisition by a swept encoding pulse, leading to a quadratic spin evolution phase that can avoid folding artefacts even upon zooming along the low‐bandwidth (SPEN) axis. By contrast to what occurs in interleaved EPI, subsampling this axis during acquisition therefore does not bring about image folding effects; it only leads to lower resolution SPEN images. If available, resolution can then be improved by relying on multiple‐coil information, which then provides missing data in the spatial rather than in the usual k‐ domain .…”

“…Despite the potential of these experiments, a relatively long acquisition readout train that depends on this gradient's slew rate and strength, ends up limiting the actual resolution of single‐scan SPEN MRI. As mentioned, this can be improved by the use of data interleaving . When implemented within the context of diffusion MR experiments, however, such multishot acquisitions call for care because they need to deal with the systematic and the random shot‐specific motions that invariably take place in in vivo experiments.…”

“…As mentioned, this can be improved by the use of data interleaving. 25 When implemented within the context of diffusion MR experiments, however, such multishot acquisitions call for care because they need to deal with the systematic and the random shot-specific motions that invariably take place in in vivo experiments. Due to the bipolar gradients involved in diffusion-weighting experiments, this will affect the image outcome in a shotspecific way and lead to sizable artefacts.…”