Fast Magnetic Resonance Simulation Using Combined Update with Grouped Isochromats

Abstract: This work aims to overcome an assumption of conventional MR simulators: Individual isochromats should be simulated individually. To reduce the computational times of MR simulation, a new simulation method using grouped isochromats is proposed. When multiple isochromats are grouped before simulations, some parts of the simulation can be shared in each group. For a certain gradient type, the isochromats in the group can be easily chosen for ensuring that they behave the same. For example, the group can be defined as the isochromats whose locations along x-axis, T1, T2 and magnetic field inhomogeneity values are the same values. In such groups, simulations can be combined when a pulse sequence with the magnetic field gradient along x-axis only are processed. The processing times of the conventional and proposed methods were evaluated with several sequences including fast spin echo (FSE) and echo-planar imaging (EPI) sequences. The simulation times of the proposed method were 3 to 72 times faster than those of the conventional methods. In the cases of 27.5 million isochromats using single instruction multiple data (SIMD) instructions and multi-threading, the conventional method simulated FSE and EPI sequences in 208.4 and 66.4 seconds, respectively. In the same cases, the proposed method simulated these sequences in 38.1 and 7.1 seconds, respectively.