Apparatus and methods which employ a primary source mirror to scan a conductive sample containing an electric current to determine the distribution of currents in the sample, providing location, total magnitude, and direction in three dimensions of each component of the electric current distribution, by means of measuring the magnetic field external to the sample. The cannula includes a housing having a proximal portion and a distal portion. The assembly in one or more embodiments operates as an intelligent node in an AMR network, and it interprets a received closure command as a closure condition.