Tracking of object movements for artefact suppression in magnetic induction tomography (MIT)

One main difficulty in MIT is that movements of the object to be imaged can
cause signal changes which are in the same order of magnitude or even higher than the wanted
signals from the interior of the body. As patient fixation is unwanted and not always possible
the best way to correct for movement artefacts is tracking of changes of the surface boundary.
As additional sensors are, in general, undesirable we suggest retrieving the tracking
information directly from the MIT signals. The basic idea is to place on the surface of the body
a set of strategically placed active markers which consist of small loops of a very thin wire
which can be opened and shorted via a tiny switch. When the loop is open it does not allow
eddy currents to flow and therefore it is invisible in the reconstructed image. When the switch
is closed, strong eddy currents flow and the signal essentially yields information on the marker
positions. Our switches are remotely controlled MOSFETs mounted in a zone of low
sensitivity of the coils so that they do not cause additional eddy currents. Image reconstruction
then once provides the body information and the marker positions separately.