Inside-out echo-planar imaging method for shortening echo time

Abstract

The invention discloses an inside-out echo-planar imaging method for shortening echo time. The method is characterized in that: a k-space trajectory extends to the outer side of a phase encoding direction from the center, wherein a gradient for generating the trajectory is composed of reading-out gradients which switch between forward and reverse directions and phase encoding gradients which switch between forward and reverse directions and gradually increases from zero. The method further comprises a step that: in order to accommodate the phase encoding gradients of which the area increases gradually without adding an echo spacing, the phase encoding gradient and a data collecting window are permitted to be overlapped. According to the method disclosed by the invention, an effective echo time in a sequence is located in the center of a first echo, the echo time is shortened greatly, and the signal to noise ratio is increased; since the contrast ratio of an image depends on signals of a k-space centre, and data of the k-space center are from an initial echo, T2 or T2* weighing of the obtained image is very small; and in diffusion imaging and arterial spin labeling imaging, the decreasing of the T2 or the T2* weighing is beneficial to improving the quality of the image.

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 spectrum 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 ...

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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