MRI using faster multiplexed echo planar imaging (EPI) pulse sequences

摘要

An MRI scanner and an MRI method that effectively reduce the inherent difference in timing of TE in the SIR images by using alternating polarity of the slice selective gradient pulse Gs and corresponding alternate polarity in RF phase offset in the excitation pulse. By using alternating polarity selective gradients, the refocusing gradient pulse on the Gs axis can be eliminated between the excitation pulses so that the time spacing between the multiple SIR excitation pulses is reduced, and therefore the time delay between onset of slice signal decay is reduced. This results in an earlier possible TE of the first excited slice, hence less signal decay and higher SNR, and overall the TE of different slices can be more nearly the same.

主权项

1. A magnetic resonance imaging (MRI) method comprising:
applying, to a subject in an MRI scanner, a set of S radiofrequency (RF) multiband excitation pulses each of which simultaneously excites M respective slices in the subject in a simultaneous image refocusing pulse sequence, wherein S>1 and M>1; applying to the subject a set of slice selective magnetic gradient pulses on a Gs axis that alternate in polarity in a timed relationship with said RF excitation pulses, without requiring refocusing magnetic gradient pulses on the Gs axis timed with the RF pulses, thereby reducing time delays between onset of MRI signals created by the respective RF pulses; acquiring MRI signals with at least one set of RF receiver coils;
computer-processing the MRI signals acquired with said RF receiver coils to produce magnetic resonance image data for respective slices of the subject; and further computer-processing at least some of said magnetic resonance image signals to produce magnetic resonance images of at least some of said slices of the subject.