Generalized susceptibility voxel convolution can be a fast and reliable way to compute susceptibility-induced B when the susceptibility source is not colocated with the B target volume of interest, as in modeling B variations from motion and foreign objects.

To demonstrate the high-resolution numerical simulation of the respirationinduced dynamic B 0 shift in the head using generalized susceptibility voxel convolution (gSVC). Materials and Methods: Previous dynamic B 0 simulation research has been limited to low-resolution numerical models due to the large computational demands of conventional Fourier-based B 0 calculation methods. Here, we show that a recentlyproposed gSVC method can simulate dynamic B 0 maps from a realistic breathing human body model with high spatiotemporal resolution in a time-efficient manner. For a human body model, we used the Extended Cardiac And Torso (XCAT) phantom originally developed for computed tomography. The spatial resolution (voxel size) was kept isotropic and varied from 1 to 10 mm. We calculated B 0 maps in the brain of the model at 10 equally spaced points in a respiration cycle and analyzed the spatial gradients of each of them. The results were compared with experimental measurements in the literature. Results:The simulation predicted a maximum temporal variation of the B 0 shift in the brain of about 7 Hz at 7T. The magnitudes of the respiration-induced B 0 gradient in the x (right/left), y (anterior/posterior), and z (head/feet) directions determined by volumetric linear fitting, were < 0.01 Hz/cm, 0.18 Hz/cm, and 0.26 Hz/cm, respectively. These compared favorably with previous reports. We found that simulation voxel sizes greater than 5 mm can produce unreliable results. Conclusion:We have presented an efficient simulation framework for respirationinduced B 0 variation in the head. The method can be used to predict B 0 shifts with high spatiotemporal resolution under different breathing conditions and aid in the design of dynamic B 0 compensation strategies.

Purpose Most previous work on the calculation of susceptibility‐induced static magnetic field (B0) inhomogeneity has considered strictly unidirectional magnetic fields. Here, we present the theory and implementation of a computational method to rapidly calculate static magnetic field vectors produced by an arbitrary distribution of voxelated magnetization vectors. Theory and Methods Two existing B0 calculation methods were systematically extended to include arbitrary orientations of the magnetization and the magnetic field; they are (1) Fourier‐domain convolution with k‐space‐discretized (KD) dipolar field, and (2) generalized susceptibility voxel convolution (gSVC). The methods were tested on an analytical ellipsoid model and a tilted human head model, as well as against experimentally measured B0 fields induced by a stainless‐steel implant located in an inhomogeneous region of a clinical 3T MRI magnet. Results Both methods were capable of correctly calculating B0 fields inside a magnetized ellipsoid in all tested orientations. The KD method generally required a larger grid and longer computation time to achieve accuracy comparable to gSVC. Measured B0 fields due to the implant showed a good match with the gSVC‐calculated fields that accounted for the spatial variation of the applied magnetic field including the radial components. Conclusion Our method can provide a reliable and efficient computational tool to calculate B0 perturbation by magnetized objects under a variety of circumstances, including those with inhomogeneous magnetizing fields, anisotropic susceptibility, and a rotated coordinate system.