Simple and convenient nuclear magnetic resonance gradient waveform distortion pre-correction method

A technology of nuclear magnetic resonance and waveform distortion, applied in magnetic resonance measurement, measurement using nuclear magnetic resonance image system, measurement of magnetic variables, etc., can solve the problems of prolonging scanning time, long measuring time, difficult to measure accurately, etc., and shorten scanning Time, stable and reliable results

Pending Publication Date: 2021-04-09
HARBIN MEDICAL UNIVERSITY
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Problems solved by technology

[0004] For the above two methods, the first gradient waveform distortion correction method needs to measure the frequency response of the gradient system, the process is complicated, the measurement time is long, and it is often difficult to measure accurately in practice; the second method prolongs the scan time, and In practical applications, the accuracy of measuring gradient waveforms is also easily affected by the geometric structure of the object, and there is a certain risk of measurement failure
In addition, in some cases, such as the half-pulse design of two-dimensional ultra-short echo time imaging, the slice selection gradient must approach the ideal waveform, and the second type of method cannot be applied at this time

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  • Simple and convenient nuclear magnetic resonance gradient waveform distortion pre-correction method
  • Simple and convenient nuclear magnetic resonance gradient waveform distortion pre-correction method
  • Simple and convenient nuclear magnetic resonance gradient waveform distortion pre-correction method

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Embodiment 1

[0034] Such as figure 1 As shown, the flow chart of the gradient waveform distortion pre-correction method of the present invention is as follows figure 1 As shown, its essence is an iterative optimization process.

[0035] A simple NMR gradient waveform distortion pre-correction method, comprising the following steps:

[0036] (1) In the first step of rectification (iteration times i=1), first load the ideal gradient waveform in the gradient generator, that is, S gg (i=1,t)=S ideal (t), the gradient waveform is distorted after passing through the gradient system, and the gradient waveform S in the imaging space is measured by the MRI sequence method vol (i=1,t), according to S vol (i=1,t) and S ideal (t) can roughly estimate the system response of the gradient system in a certain frequency band, and obtain the approximate system impulse response h(t). Using the linear time invariant (LTI) characteristic of the gradient system, the system can be estimated by formula (5) ...

Embodiment 2

[0053] This embodiment is basically the same as Embodiment 1, the difference is that in step (1), according to S vol (i=1,t) and S ideal (t) The system response of the gradient system in a certain frequency band can be roughly estimated. For the trapezoidal wave, the differential operation can be directly performed on the gradient waveform, namely:

[0054] h(t)≈c arb *D(S vol (i=1,tramp )) (4)

[0055] Among them, c arb is the normalization constant, T ramp You can choose a certain gradient platform time after the rising edge according to the actual situation, just pay attention to avoid the influence of the gradient falling edge, h(t) is the approximate system impulse response. This estimation method is more accurate when the gradient climbing rate is high and the gradient plateau time is long.

Embodiment 3

[0057] This embodiment is basically the same as Embodiment 1 or 2, except that in step (3), the gradient system response is estimated in each iteration to obtain the system impulse response h(t).

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Abstract

The invention provides a simple and convenient nuclear magnetic resonance gradient waveform distortion pre-correction method. The method comprises the following steps: 1, correcting: loading an ideal gradient waveform, namely Sgg (i = 1, t) = Sideal (t), in a gradient generator, generating distortion after the gradient waveform passes through a gradient system, obtaining a gradient waveform Svol (i = 1, t) in an imaging space through a sequence method, and estimating a gradient system response according to the Svol (i = 1, t) and the Sideal (t) to obtain a system impulse response h (t); correcting distortion of the Svol (i = 1, t) relative to the Sideal (t), performing next iteration, and updating an output gradient waveform Sgg (i + 1, t); and iterating for multiple times until the distortion of the Svol (i = 1, t) is minimum, and repeating the following steps to obtain a pre-corrected gradient waveform database. The method does not need to specially measure the frequency response of the gradient system, is more stable and reliable, does not need pre-scanning, and can adapt to scanning in any geometric orientation.

Description

technical field [0001] The invention relates to the technical field of magnetic resonance imaging, in particular to a simple pre-correction method for nuclear magnetic resonance gradient waveform distortion. Background technique [0002] Gradient pulse is very important in magnetic resonance imaging (MRI). On the one hand, combined with radiofrequency pulses, it determines the excitation profile of the tissue; on the other hand, although current MRI introduces the concepts of RF coding and coil sensitivity coding, gradient coding is still the most important spatial coding method. However, due to the inductance of the gradient coil, the bandwidth limitation of the gradient amplifier, and the conductor structure in the magnet space, the actual magnetic field gradient generated in the imaging space always deviates from the ideal gradient waveform designed in the MRI imaging sequence. This is the so-called gradient waveform deformation or waveform distortion. Distortion of the...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R33/54
CPCG01R33/54
Inventor 孙夕林王凯官小红杨春升吴丽娜杨丽丽潘贞明王浩宇王凯琦王丽姣韩睿
Owner HARBIN MEDICAL UNIVERSITY
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