An inside-out echo-planar imaging method for shortening echo time

Abstract

Disclosed is an inside-out echo planar imaging method for reducing echo time. In the method, a k-space track gradually extends from the middle to the outer side in the phase encoding direction; the track-generating gradient consists of a reading-out gradient switching between forward and reverse directions and a phase encoding gradient switching between forward and reverse directions and having an area gradually increasing from zero. The method further comprises: the phase encoding gradient and a data acquisition window are allowed to overlap in order to accommodate the phase encoding gradient having a gradually increasing area without increasing the echo gap. In the sequence of the method, the effective echo time is in the center of a first echo, therefore the echo time is greatly reduced and the signal to noise ratio is correspondingly improved. Image contrast depends on a signal in the k-space center, and the data of the k-space center originates from an initial echo, therefore the obtained image has a very small T2 or T2* weight. In the diffusion imaging and arterial spin labeling imaging, the reduction of the T2 or T2* weight helps to improve image quality.

Description

technical field [0001] The invention relates to the field of magnetic resonance imaging, in particular to an inside-out planar echo imaging method. Background technique [0002] The echo planar imaging (EPI) sequence is one of the fastest of the MRI sequences. With the advent of modern gradient systems and radio frequency systems, it takes only tens of milliseconds for EPI to generate a two-dimensional image. It is precisely because of its fast imaging speed that EPI plays a vital role in applications such as diffusion imaging, perfusion imaging, brain function mapping imaging, cardiac imaging, dynamic research, and real-time imaging. In single-shot EPI, a complete two-dimensional k-space data is acquired with a single RF excitation pulse and a series of echo trains, with very high temporal resolution. However, EPI has high hardware requirements, produces low-resolution images and can produce significant artifacts. The artifacts include Nyquist artifacts, chemical shift a...

AI Technical Summary

Problems solved by technology

The third method is to stimulate the EPI multiple times to increase the number of excitations to obtain a shorter echo time, and the acquisition time of the multiple-shot EPI is correspondingly increased, and it is also more sensitive to motion

It can be seen that none of these three methods can effectively shorten the echo time

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