| 主权项 |
1. A method of correcting warping of an acquired image in an MRI system, caused by non-linearities in gradient field profiles of gradient coils, comprising:
a) constructing a computer model representing conducting pathways for each gradient coil in said MRI system; b) calculating a predicted magnetic field at each point in space for each said gradient coil in said model; c) measuring actual magnetic field at each point in space for each said gradient coil in said MRI system; d) verifying accuracy of said model by comparing said predicted magnetic field to said actual magnetic field at each said point in space and in the event said model is not accurate then repeating a)-d), and in the event said model is accurate then; e) constructing a distortion map for mapping coordinates in real space to coordinates in warped space of said acquired image based on deviations of said predicted magnetic field from linearity; and f) unwarping said warping of the acquired image using said distortion map,
wherein said predicted magnetic field is calculated using one of either Biot-Savart equations or an equivalent thereof,wherein said distortion map is constructed for mapping each point x,y,z in real space to a point x′,y′,z′ of the image in warped space by obtaining B(x,y,z) values from said Biot-Savart equations or equivalent for each said gradient coil,wherein values of x′, y′ are computed directly from k-space data using inverse gridding from uniform to non-uniform sample locations, andwherein said inverse gridding is effected by performing an apodization correction in k-space, followed by an Inverse Fourier Transform and then using convolution interpolation in image space with a Kaiser-Bessel kernel. |
