Towards direct non-invasive detection of cardiac biomagnetism via balanced Rotary Excitation

Motivation: Previous work proved the basic feasibility of detecting magnetic stimulus fields modelled on cardiac biomagnetism in phantom experiments. For application in a human subject, the sequence must be adapted to the challenging field properties in the in vivo experiment. Goal(s): Comparison of compensated spin-locking modules to identify the module with lowest susceptibility to field inhomogeneities. Approach: The interfering influence of ΔB0 on field detection using different preparation modules was investigated in simulation and phantom experiments. Results: The composite spin-lock and balanced spin-lock modules show increased robustness at field deviations realistic for in vivo cardiac applications. However, the signal amplitude is reduced by 67%. Impact: Rotary Excitation (REX)-based field detection provides high sensitivity to pulsed-magnetic fields and is therefore a promising approach for imaging of cardiac biomagnetism. Advancing the REX sequence to reduce sensitivity to B0 inhomogeneities is essential for its application in vivo.