In vivo validation of distributed source solutions for the biomagnetic inverse problem

Probabilistic modelling of continuous current sources is applied to the analysis of MEG signals generated by current dipoles implanted in the head of a living human subject. Estimates of the distribution of activity within a circular disk are obtained from signals generated by a single implanted dipole and by a pair of simultaneously active implanted dipoles. The orientation and depth of the disc is determined in advance from the experimental geometry and the measurements. The resulting reconstructions constitute the first in vivo validation of distributed source imaging; they provide a complementary test to earlier works using computer generated data and tests using point source analysis of signals generated by a single implanted dipole. In this work we provide a literal test of spatial resolution by resolving two nearby point-like sources. Temporal resolution is addressed in a de facto manner by imaging at one millisecond intervals. Computer simulations, with controlled amount of noise, are used to demonstrate the robustness of the results, and show the interplay between high spatial accuracy and noise insensitivity.