MRI simulation and reconstruction framework for arbitrarily-oriented encoding and transmit/receive magnetic vector fields

Conventional MRI is relying on the assumption of the magnetic field B₀ being homogeneous in direction and amplitude. However, with the growing interest in portable, affordable point-of-care MRI systems, these assumptions do not necessarily hold anymore due to compromises necessary to achieve a reduction in e.g. footprint, weight and portability. Simulation software may help by interpreting artifacts from concomitant fields or evaluation of new encoding schemes which are optimized for non-ideal hardware but also with the design of new scanner designs. In this work, a MATLAB-based simulation framework was developed capable of dealing with the full magnetic field vectors for B₀, the spatial magnetic encoding fields (SEMs), and the transmit/receive fields enabling the evaluation of arbitrary magnetic field configurations for encoding in MRI. For that, conventional matrix-based Bloch simulation is generalized, evaluated and validated, achieving substantially shorter simulation time. Furthermore, it is used to predict image quality in 2D gradient echo experiments with deflected magnetic fields. The comparison of numerical Bloch and the adapted matrix-based simulation revealed close agreement of both reconstructed images. Further, it was shown that compensation of the associated artifacts can be achieved by incorporating knowledge about the used magnetic fields into the reconstruction process. The presented and validated software package enables full consideration of arbitrarily-oriented SEMs, B₀ and transmit/receive magnetic fields used in MRI for signal simulation but also reconstruction removing the related artifacts. As such, the software might become a valuable tool for new low-field system designs and the investigation of new reconstruction algorithms.