A method of analysing biomagnetic signals is presented which focuses attent
ion on activity in a specific region of interest. The method is based on th
e construction of virtual sensors, corresponding to linear combinations of
lead fields that are optimally localized within the region of interest. Thi
s method is fast and stable. It is tested against physiologically plausible
computer generated signals and also against more elaborate analysis of rea
l data. The results show that the method can be very effective as a fast sc
anning tool identifying activity from pre-defined regions of interest.