A Miniature, Fiber-Optic Vibrometer for Measuring Unintended Acoustic Output of Active Hearing Implants during Magnetic Resonance Imaging.

Guy Fierens,Christ Glorieux,Joris Walraevens,Ronald Peeters,Nicolas Verhaert

doi:10.3390/s21196589

Abstract

Making use of magnetic resonance imaging (MRI) for diagnostics on patients with implanted medical devices requires caution due to mutual interactions between the device and the electromagnetic fields used by the scanner that can cause a number of adverse events. The presented study offers a novel test method to quantify the risk of unintended output of acoustically stimulating hearing implants. The design and operating principle of an all-optical, MRI safe vibrometer is outlined, followed by an experimental verification of a prototype. Results obtained in an MRI environment indicate that the system can detect peak displacements down to 8 pm for audible frequencies. Feasibility testing was performed with an active middle ear implant that was exposed to several pulse sequences in a 1.5 Tesla MRI environment. Magnetic field induced actuator vibrations, measured during scanning, turned out to be equivalent to estimated sound pressure levels between 25 and 85 dB SPL, depending on the signal frequency. These sound pressure levels are situated well below ambient sound pressure levels generated by the MRI scanning process. The presented case study therefore indicates a limited risk of audible unintended output for the examined hearing implant during MRI.

Highlights

In medicine, magnetic resonance imaging (MRI) has become a commonly used technique for non-invasive diagnostics of many pathologies
Additional risks arise when exposing a patient with an implanted medical device to an MRI environment as the, often conductive or metallic, implant and the scanner mutually interact, creating unwanted and even hazardous situations [4,5,6]
An approximate Gaussian light beam exited the end of a plastic optical fiber and diverged conically when traveling through an air gap before being partly captured by a second, coaxially located second plastic optical fiber

Summary

Introduction

Magnetic resonance imaging (MRI) has become a commonly used technique for non-invasive diagnostics of many pathologies. MRI is not completely without risk and a number of adverse events have been reported over the years, including severe skin burns [1,2] and lethal accidents due to magnetically induced forces [3]. Additional risks arise when exposing a patient with an implanted medical device to an MRI environment as the, often conductive or metallic, implant and the scanner mutually interact, creating unwanted and even hazardous situations [4,5,6]. Several severe adverse events have been reported with medical devices, including excessive local heating, unintended electrical stimulation, movement of implanted aneurysm clips or paralysis due to heating-induced brain lesions [3,7]

Methods

Results

Conclusion