Effects of Different Head Models in Wearable OPM-MEG

Optically pumped magnetometer (OPM)-based magnetoencephalography (MEG) has attracted significant attention due to its flexible sensor configuration and closer proximity to the scalp. The source localization technique of MEG is used in neuroscience and clinical research. Different head models have been developed to provide a forward solution for MEG source localization. However, the effects of different head models have not yet been studied under the new OPM-MEG measurement scenario. In this simulation study, we investigated the effects of eight head models [a local sphere (LS), a corrected sphere (CS), a boundary element method (BEM)-based, and five finite-element method (FEM)-based models, including isotropic three-, four-, and five-compartment and two anisotropic five-compartment head models] for forward and inverse solutions. In addition, we studied the effects of these eight head models in a more realistic environment, such as under sensor coregistration error and measurement noise. The results showed that the source localization error (LE) between the simplified head model and the isotropic five-compartment FEM model can reach 4-5 mm, emphasizing the necessity of using an elaborate head model. In addition, in the comparison of forward and inverse problems, the distinction of cerebrospinal fluid (CSF) showed the most obvious improvement. Thus, an FEM head model with a CSF compartment is recommended. Furthermore, a high level of measurement noise (>80%, the ratio of root mean square of the noise matrix to the data matrix) and high coregistration errors (rotation error > 2°) significantly reduced the contributions of realistic head models.