Optical co-registration method of OPM-MCG and MRI based on skin markers

The emergence of optically pumped magnetometers (OPMs) has advanced magnetocardiography (MCG). MCG data must be co-registered with anatomical images for source localization. While optical scanning provides a high-precision co-registration approach, it is incompatible with the co-registration of OPM-MCG and magnetic resonance imaging (MRI). In this study, we propose an optical co-registration method for OPM-MCG and MRI based on skin markers. First, we design the structure and layout of skin markers suitable for MRI. Subsequently, the imaging regions of skin markers in MRI are identified using principal component analysis (PCA) and particle swarm optimization (PSO), followed by the reconstruction of their external surfaces via the iterative closest point (ICP) algorithm. Finally, the OPM sensors are registered to the MRI coordinate system by optical scanning. Phantom-based evaluation experiments show that the average co-registration error of sensor positions is 0.6 mm. In addition, the single-subject experiment show that the present method achieves the lowest average torso surface fitting error, which effectively reduces the registration error caused by factors such as respiration. The proposed radiation-free co-registration method with high accuracy facilitates future applications of OPM-MCG, which may particularly benefit pediatric and pregnant populations.