Synthesis of 4D Flow MRI Data using Particle-based Bloch Simulations in CMRsim

Motivation: Signal model-based synthesis of 4D flow MRI data from CFD is promising to study image acquisition, reconstruction methods and augment data for inference. However, the approach assumes idealized encoding, and particle-based Bloch simulations are needed to include complex effects. Goal(s): Implement a particle-based Bloch simulation in CMRsim for generating synthetic multi-venc 4D flow data. Approach: Using pulsatile, stenotic U-bend CFD data as input, simulations of moving magnetization in CMRsim generate synthetic 4D flow MRI data. Results: 4D flow simulation is feasible in CMRsim, demonstrating tractable simulation times and good agreement with ground truth and magnetization history-based effects, namely acceleration and intra-voxel dephasing. Impact: Numeric Bloch simulations in CMRsim permit a detailed study of imaging protocol-dependent flow-related artifacts in 4D flow MRI of complex flows and can thereby assist in improving acquisition and reconstruction approaches.