Method for shimming first order of magnet

A magnet and main magnetic field technology, applied in magnetic resonance measurement and other directions, can solve problems such as time-consuming and unsatisfactory final results

Inactive Publication Date: 2009-12-16
北京海思威科技有限公司
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Problems solved by technology

[0008] The advantage of the maximum signal method in active shimming is that it is intuitive and easy to implement. The disadvantage is that it needs multiple optimization iterations to get the best shimming effect, which takes a long time and the final result is often not ideal.
Other methods, such as phase diagram method, chemical shift method, etc., take longer and are often not suitable for permanent magnet MRI systems

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  • Method for shimming first order of magnet

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Embodiment 2

[0089] Embodiment two, applying such as Figure 6 In the shimming pulse sequence shown, the first echo collected is a stimulated echo (non-gradient echo), and the second echo is a gradient echo. The relevant parameters of the shimming pulse sequence are as follows: Gr i 、Gr j are the amplitudes of the gradient pulses corresponding to the first and second pulse sequences respectively, that is, the amplitude of the read gradient, 2τ i , 2τ j are the pulse widths of the gradient pulses of the first and second pulse sequences, and are also the sampling times of the first and second echo signals. Ideally, the echo times of the first and second echo signals are respectively TE i 、TE j (TE i ≠TE j ), the echo deviation time of the first and second echo signals are respectively t i , t j , and the corresponding reference echo deviation time is t′ i , t' j , time difference Δt=t j -t i , Δt'=t' j -t' i .

[0090] Set Be i (t), Be j (t) are the gradients of the magnetic...

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Abstract

The invention relates to a method for actively shimming first order of a main magnet in a nuclear magnetic resonance measurement (NMR) system and a magnetic resonance imaging (MRI) system. The method comprises the steps of carrying out shimming on three directions orthogonalized in space, using echo deflection time as measurement of first order nonhomogeneity of a main magnetic field, using a linear relationship between difference of two echo deflection times and the first order nonhomogeneity gradient under a certain approximate condition so as to determine the first order nonhomogeneity gradient of the main magnetic field, changing absolute measurement to relative measurement, transforming calculation of determining the nonhomogeneity of the main magnetic field according to the phase position from calculation of determining the nonhomogeneity of the main magnetic field according to time through the Fourier transformation on the echo, and using slope of a straight line after multimetering linear fitting to replace calculation on single-point data. Meanwhile, the method can acquire quantitative data of vortex to provide solution for eliminating the vortex. The method remarkably improves the measurement precision, reduces number of iterations, accelerates shimming, and can be used for any magnet in NMR and MRI system.

Description

technical field [0001] The present invention relates to a new technique for first-order active shimming of main magnets in nuclear magnetic resonance measurement (NMR) and magnetic resonance imaging (MRI) systems. Background technique [0002] Magnetic resonance imaging (MRI) is realized on the basis of the polarization of the sample by the main magnetic field, the excitation of the sample by the radio frequency field, and the precise positioning of the imaging position by the gradient field. The signal measured during the magnetic resonance imaging process comes from the resonance between the frequency pulse of a specific frequency and the spin nuclear magnetic moment. Due to the inhomogeneity of the main magnetic field, the resonance peak width of the free decay signal (FID: Free Induction Decay) is greatly affected. The width of the resonance peak greatly affects the quality of imaging. Therefore, all MRI systems and NMR spectra involve the shimming of the main magnetic f...

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R33/38
Inventor 包尚联何群周堃
Owner 北京海思威科技有限公司
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