Abstract: The present disclosure discloses a method for automatically identifying south troughs by improved Laplace and relates to the technical field of meteorology. The method includes the following steps: acquiring grid data of a geopotential height field; calculating a gradient field of the geopotential height field in an x direction; searching for a turning point where a gradient value turned from being negative to being positive, and cleaning the gradient field; calculating a divergence of the x direction to obtain an improved Laplacian numerical value L?; performing 0,1 binarization processing on the L? to obtain a black-and-white image and a plurality of targets of potential troughs, merging the black-and-white image and the plurality of targets of the potential troughs by expansion, recovering original scale through erosion, and selecting an effective target through an angle of direction of a contour and an axial ratio.

Abstract: Fast spin echo pulse sequences are adjusted to reduce, or eliminate image artifacts caused by Maxwell terms arising from the linear imaging gradients. The waveforms of the slice selection, phase encoding and readout gradients are adjusted in shape, size or position to eliminate or reduce the phase error caused by the spatially quadratic Maxwell terms.

Abstract: A method is presented for correcting Maxwell term error artifacts produced by an NMR system during the production of either a phase contrast angiogram or a complex difference angiogram. Phase corrections are made to the reconstructed phase image to eliminate the artifacts. Correction coefficients calculated from the flow encoding magnetic gradient waveforms of the phase contrast pulse sequence are used in a polynomial to calculate a set of phase error corrections. These corrections are then used to adjust the phase at each pixel of the angiogram image.

Abstract: Artifacts in NMR images produced by Maxwell terms during non-rectilinear scans, such as spiral scans, are reduced or eliminated. Phase corrections for in-plane and through-plane blurring are used to offset Maxwell terms errors.