Steady-state procession gradient multi-echo water and grease separation imaging method

Abstract

The invention discloses a steady-state procession gradient multi-echo water and grease separation imaging method. The steady-state procession gradient multi-echo water and grease separation imaging method comprises the following steps of on the basis of a steady-state procession imaging sequence for conventional scanning on a magnetic resonance imaging system, repeatedly exciting the imaging area by a radio frequency pulse at the interval of 10ms magnitude or smaller short cycle TR; setting a pulse flip angle into +alpha / 2 in a first sequence repetition cycle, and eliminating the sampling period; alternatively setting the pulse flip angle into +alpha and -alpha in the subsequent sequence repetition cycle; using the layer selection gradient, phase encoding gradient and frequency encoding gradient to perform three-dimensional encoding, wherein the sum of integral areas of gradients in each bearing is zero, and the proton magnetizing vector procession is approximate to the steady state; enabling the magnetizing vectors to form three or two gradient echoes under the action of three or two positive and negative alternating frequency encoding gradients in each TR period, wherein the integral area of gradients in the frequency encoding direction is zero; performing direct phase encoding on the three or two echoes according to echo peak interval and water and grease chemical displacement difference value.

Description

technical field [0001] The invention relates to the technical field of nuclear magnetic imaging, in particular to a steady-state precession gradient multi-echo water-fat separation imaging method. Background technique [0002] Chemical shift imaging is currently one of the most effective magnetic resonance fat suppression imaging techniques, and it is widely used in the diagnosis of extremities and joints. However, for moving organs such as the abdomen, the clinical application of this type of fat suppression technology is often limited due to motion artifact interference . The development of scanning acceleration technology has always been an important direction of clinical MRI academic research and commercial application, which not only helps to improve the efficiency of clinical examination of MRI imaging technology but also helps to overcome motion artifact interference. So far, a variety of general-purpose scan acceleration technologies, such as parallel acquisition, h...

AI Technical Summary

Problems solved by technology

[0003] In recent years, there are mainly three versions of the steady-state precession water-fat separation imaging method that have been initially successfully developed in European and American laboratories such as Stanford University. One of the versions is to set the steady-state precession based on the resonance frequency difference Δf between water and fat. The echo times of the sequence are TE, TE+1 / Δf / n and TE+1 / Δf / n (n is any positive integer), and three independent scans are performed to obtain three images, which are then fitted by the least square method For water image and fat image, the scan time is three times longer than that of the conventional steady-state precession scan; the second version is that each scan uses different TE and TR parameter values ​​and detects each The phase difference between the real part and the imaginary part of the first echo needs to be precisely controlled to 90 degrees. This scanning method is very sensitive to pulse flip angle, RF phase and off-resonance effects. In the actual clinical environment The down-scanning time is long, and it is difficult to reasonably select TE and TR for the separation of different echo components; the third version is to combine the two-point Dixon water-fat separation technology with the steady-state precession technology, based on The bipolar frequency encoding gradient detects two echoes simultaneously in one sequence period, one is the in-phase water-fat signal and the other is the reverse-phase water-fat signal, and then the water-fat signal is assigned based on the traditional two-point Dixon image reconstruction method, However, there may be errors in the attribution of water-fat signals at the water-fat junction, which is mainly suitable for high-field pancreaticobiliary water imaging

In addition, the above method basically does not consider the eddy current effect, remanence effect and phase winding problems that may be caused by long echo time, and is not universally applicable to various types of MRI equipment

Images