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Using transient FE models to assess anatomical influences on electrical stimulation

Author(s):

A. Kuhn
Conference/Journal:

FEM Workshop, Ulm, vol. 12
Abstract:

In transcutaneous electrical stimulation, pairs of electrodes are placed on the human body in order to apply current pulses. The electrical current elicits action potentials in the nerves, which lead to muscle contraction. Clinical trials show that different people do not have the same activation current in order to get the same muscle activation. We used finite element (FE) modelling to simulate the influence of the human anatomy on electrical stimulation. Possible influences are the location of the nerve, the thickness of the different fat layers, and geometry of bone and muscles. In past publications the scalar potential inside the volume conductor was calculated with static solvers. Because of the presence of capacitive effects in the tissue layers, the resulting potentials are time dependent. We have therefore used a transient solver and verified the time dependent potentials with intramuscular and external voltage measurements on human volunteers. The geometry of the FE model was determined from segmented MRI data. The MRI scans were performed on three people's forearms. The influence from inhomogeneities was investigated in order to find out how much detail has to be included in the geometry of the FE model. We found that the influence from bone on a nerve fibre can be assumed to be negligible if there is at least a distance of 0.5 cm between nerve and bone even though bone has a much higher resistance than muscle. The nerve depth was found to have the major influence on nerve activation. As a result the local fat thickness has also a big influence. We concluded that it is important to incorporate MRI data if subject dependent studies are carried out. However, for general investigations (e.g. optimize electrode shapes or arrangements) it is sufficient to use a multiple layer cylinder model of the forearm.

Year:

2005
Type of Publication:

(06)Talk
Supervisor:

M. Morari

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