Tierney develops the signal-processing and array-design methods that make OPM-MEG usable in practice, including spherical-harmonic and vector-based interference rejection that exploits the multi-axis, on-scalp geometry of OPM arrays. He works on optimal spatial sampling of the neuromagnetic field, the trade-offs between sensor count and placement, and SPM-based source reconstruction. He also led several of the early clinical OP-MEG validation studies.