Magnetic resonance dynamic shimming method

Abstract

The invention discloses a magnetic resonance dynamic shimming method, which sequentially comprises the following steps: 1, performing static active shimming to remove first-order B0 field components of a whole space; 2, acquiring three-dimensional B0 field data; 3, calculating residual high-order B0 field distribution through the acquired three-dimensional B0 field data; 4, fitting a first-order B0 field in the layer by layer, and calculating dynamic shimming parameters in two directions in the layer; 5, deducting the dynamic shimming component applied in the step 4 by simulation from the residual high-order B0 field distribution to obtain a residual high-order B0 field; 6, performing phase unwrapping operation on the residual high-order B0 field; 7, calculating a 0-order field layer by layer, and calculating a dynamic shimming parameter perpendicular to the layer direction; and 8, applying dynamic shimming parameters layer by layer in scanning. For a magnetic resonance system with a large high-order B0 field, the shimming algorithm is more stable and reliable, and it can be ensured that magnetic field fluctuation of other positions in space is small.

Description

technical field [0001] The invention relates to the technical field of nuclear magnetic resonance imaging, in particular to a magnetic resonance dynamic shimming method. Background technique [0002] In a magnetic resonance imaging system, the homogeneity of the main magnetic field is a key factor for the quality of magnetic resonance images. The non-uniformity of the main magnetic field can lead to susceptibility artifacts, poor grease pressure, image distortion, and even artifacts. Therefore, shimming measures are usually used to improve the uniformity of the magnetic field within a specific range. [0003] Shimming measures usually include passive shimming and active shimming. Passive shimming is generally the first measure to improve the uniformity of the magnetic field during the installation of the magnet by placing iron pieces at specific positions in the magnet. Active shimming is to offset the non-uniformity of the main magnetic field by adjusting the current in ...

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Problems solved by technology

[0011] 1) The derivation operation will amplify the noise and reduce the reliability of shimming

[0012] 2) Due to the existence of a large high-order field, its first-order derivative is proportional to the distance from the center of the magnet or proportional to the (n-1) power, that is, the shimming parameters at the level of the center of the magnet and the level far away from the center of the magnet are very different. That is to say, when dynamic shimming is applied to a certain layer, other layers may be in an extremely uneven state at this moment. If a non-spatial selective pulse is applied at this time, the state of other layers will be destroyed.

For example, applying a chemical shift frequency selective fat-pressing pulse will affect the steady-state process of fat and reduce the effect of fat-pressing, and may also excite water components in other layers, resulting in artifacts or reducing the signal-to-noise ratio

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