Objective In functional electrophysiological imaging, signals are often contaminated by interference that can be of considerable magnitude compared to the signals of interest. This paper proposes a novel algorithm for removing such interferences that does not require separate noise measurements. Approach The algorithm is based on a dual definition of the signal subspace in the spatial- and time-domains. Since the algorithm makes use of this duality, it is named the dual signal subspace projection (DSSP). The DSSP algorithm first projects the columns of the measured data matrix onto the inside and outside of the spatial-domain signal subspace, creating a set of two preprocessed data matrices. The intersection of the row spans of these two matrices is estimated as the time-domain interference subspace. The original data matrix is projected onto the subspace that is orthogonal to the interference subspace Main results The DSSP algorithm is validated first by using the computer generated data, and then by using two sets of real biomagnetic data: SCEF data measured from a healthy volunteer and MEG data from a patient with a vagus nerve stimulator. Significance The proposed DSSP algorithm is effective for removing overlapped interference in a wide variety of biomagnetic measurements.

This paper develops a novel method to reduce the influence of stimulus-induced artifacts in functional spinal cord imaging. The developed method employes a two-step procedure. The first step acquires artifact data, which contain artifacts but do not contain spinal cord evoked magnetic field (SCEF). The second step applies a method called common-mode subspace projection (CSP). The effectiveness of the developed method is validated using SCEF data measured from a healthy volunteer.