Publication Date:
2018-03-12
Description:
Purpose To demonstrate a computationally efficient and theoretically artifact-free method to calculate static field (B 0 ) inhomogeneity in a volume of interest induced by an arbitrary voxelated susceptibility distribution. Methods Our method computes B 0 by circular convolution between a zero-filled susceptibility matrix and a shifted, voxel-integrated dipolar field kernel on a grid of size N S +N T – 1 in each dimension, where N S and N T are the sizes of the susceptibility source and B 0 target grids, respectively. The computational resource requirement is independent of source-target separation. The method, called generalized susceptibility voxel convolution, is demonstrated on three susceptibility models: an ellipsoid, MR-compatible screws, and a dynamic human heartbeat model. Results B 0 in an ellipsoid calculated by generalized susceptibility voxel convolution matched an analytical solution nearly exactly. The method also calculated screw-induced B 0 in agreement with experimental data. Dynamic simulation demonstrated its computational efficiency for repeated B 0 calculations on time-varying susceptibility. On the contrary, conventional and alias-subtracted k-space-discretized Fourier convolution methods showed nonnegligible aliasing and Gibbs ringing artifacts in the tested models. Conclusion Generalized susceptibility voxel convolution can be a fast and reliable way to compute susceptibility-induced B 0 when the susceptibility source is not colocated with the B 0 target volume of interest, as in modeling B 0 variations from motion and foreign objects.
Print ISSN:
0740-3194
Electronic ISSN:
1522-2594
Topics:
Medicine
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