In-Vivo Electrical Impedance Measurement in Mastoid Bone.
Nerve monitoring is a safety mechanism to detect the proximity between surgical instruments and important nerves during surgical bone preparation. In temporal bone, this technique is highly specific and sensitive at distances below 0.1 mm, but remains unreliable for distances above this threshold. A deeper understanding of the patient-specific bone electric properties is required to improve this range of detection. A sheep animal model has been used to characterize bone properties in vivo. Impedance measurements have been performed at low frequencies (<1 kHz) between two electrodes placed inside holes drilled into the sheep mastoid bone. An electric circuit composed of a resistor and a Fricke constant phase element was able to accurately describe the experimental measurements. Bone resistivity was shown to be linearly dependent on the inter-electrode distance and the local bone density. Based on this model, the amount of bone material between the electrodes could be predicted with an error of 0.7 mm. Our results indicate that bone could be described as an ideal resistor while the electrochemical processes at the electrode-tissue interface are characterized by a constant phase element. These results should help increasing the safety of surgical drilling procedures by better predicting the distance to critical nerve structures.
Computational Biomechanics, ISTB, University of Bern, Stauffacherstrasse 78, 3014, Bern, Switzerland. thomas.wyss@istb.unibe.ch.
Thomas
0000-0002-3701-4989
T
Wyss Balmer
ARTORG Center for Biomedical Engineering, University of Bern, Murtenstasse 50, 3008, Bern, Switzerland.
Juan
J
Ansó
Control and Sensing Systems Division, CSEM, Rue Jaquet-Droz 1, 2002, Neuchâtel, Switzerland.
Enric
E
Muntane
ARTORG Center for Biomedical Engineering, University of Bern, Murtenstasse 50, 3008, Bern, Switzerland.
Kate
K
Gavaghan
ARTORG Center for Biomedical Engineering, University of Bern, Murtenstasse 50, 3008, Bern, Switzerland.
Stefan
S
Weber
Mathematics, Bern University of Applied Sciences, Quellgasse 21, 2501, Biel, Switzerland.
Andreas
A
Stahel
Computational Biomechanics, ISTB, University of Bern, Stauffacherstrasse 78, 3014, Bern, Switzerland.
Philippe
P
Büchler
D000818:Animals; D017097:Electric Impedance; D008416:Mastoid / Q000737:chemistry* / Q000378:metabolism; D012756:Sheep
Cochlear implant; Facial nerve monitoring; Nerve preservation; Resistivity