High-Resolution Numerical Simulation of Respiration-Induced Dynamic B₀ Shift in the Head in High-Field MRI

Abstract

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.

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