Gradient system time delay correction method for fast spin echo pulse sequence

Abstract

The invention provides a gradient system time delay correction method for a fast spin echo pulse sequence. In the method, a gradient system time delay is corrected by correcting a gradient pulse, and an amplitude synthetic matrix for correcting the gradient pulse is calculated by using the normalized gradient system time delay. By the method, the influence of the gradient system time delay on thefast spin echo pulse sequence is overcome, and the hardware cost and the system complexity of a magnetic resonance imaging system are not increased; and even if the gradient system time delays in x, y and z directions are unequal, the power of a gradient power amplifier is not enough to provide overshooting impulse with larger amplitude in a gradient waveform. By the method, the gradient system time delay can still be corrected so as to enhance the image quality of a sagittal plane, a coronal plane, a cross section and various diagonal planes in a fast spin echo image.

Description

technical field [0001] The present invention relates to a magnetic resonance imaging (MRI) method, in particular, to a pulse sequence correction method adopted in order to reduce the image artifacts caused by the gradient system delay in the magnetic resonance fast spin echo (FSE) imaging technology. Background technique [0002] Magnetic resonance imaging (MRI) technology has become a very useful tool in medical diagnosis. Usually, in a magnetic resonance imaging system, when the sample (patient) under test is placed in a static magnetic field B 0 (B 0 When equilibrium is reached in the direction defined as the z-axis direction of the physical coordinate system, the nuclei (nuclear spins) in the sample are affected by B 0 polarization to produce a macroscopic magnetization vector M 0 . M 0 It is rotated into the horizontal plane (xy plane) under the excitation of the radio frequency pulse, and then precesses around the z axis. A receiver coil is placed around the samp...

AI Technical Summary

Problems solved by technology

[0005] Question 1: In the magnetic resonance system, in the three gradient directions of xyz, the number of pre-emphasis channels in each direction is 3 to 5

The time constants of these channels need to be set according to the characteristics of the eddy current. Due to the small number of channels, it is difficult to accurately correct the delay of the gradient system while compensating for the eddy current

[0006] Question 2: The gradient system delay is determined by the gradient system

However, the delay of the gradient system has not changed. At this time, the delay of the gradient system cannot be corrected flexibly and accurately.

[0007] Question 3: According to the characteristics of eddy current, the signal amplitude output by each channel of pre-emphasis changes with time to meet the e-exponential decay law

[0009] Question 4: In the magnetic resonance system, there are physical coordinate system x-y-z and imaging coordinate system s-p-r (that is, layer selection direction s, phase encoding direction p, and reading direction r)

Since the gradient system delays in the x, y, and z directions are usually unequal, insufficient or excessive delay correction will cause artifacts in the FSE image

At this time, the delay of x, y, and z cannot be taken into account by this method

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