title: In situ and ex vivo evaluation of a wireless magnetoelastic biliary stent monitoring system.
abstract: This paper presents the in situ and ex vivo evaluation of a system that wirelessly monitors the accumulation of intimal tissue and sludge in a biliary stent. The sensing element, located within the stent, is a magnetoelastic resonator that is queried by a wireless radio frequency signal. The in situ testing uses a commercially-available self-expanding biliary stent enhanced with a 1 mm x 25 mm magnetoelastic ribbon sensor (formed from Metglas 2605SA1). The stent has a conformal magnetic layer (consisting of strontium ferrite particles suspended in polydimethylsiloxane) that biases the sensor. The external interrogation module is able to acquire a signal from the sensor from a distance of at least 5 cm while the sensor is implanted in a porcine carcass and loaded with biological fluids. The ex vivo testing uses bile harvested from the porcine carcass. The response of a 1 mm x 25 mm magnetoelastic ribbon sensor is first calibrated with fluids of known density and viscosity, and the calibrated sensor is used to estimate that the viscosity of the harvested bile is 2.7-3.7 cP. The test results presented in this paper illustrate the fundamental usability of the system when the sensor is implanted, loaded by biological fluids, and interrogated in a surgical setup.
authors.affiliation: Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA. greensr@umich.edu
authors.forename: Scott Ryan
authors.initials: SR
authors.lastname: Green
authors.forename: Richard S
authors.initials: RS
authors.lastname: Kwon
authors.forename: Grace H
authors.initials: GH
authors.lastname: Elta
authors.forename: Yogesh B
authors.initials: YB
authors.lastname: Gianchandani
mesh_terms: D000818:Animals; D001646:Bile / Q000737:chemistry*; D001662:Biliary Tract Surgical Procedures / Q000295:instrumentation*; D055119:Elastic Modulus; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D015607:Stents; D013552:Swine; D013686:Telemetry / Q000295:instrumentation*