Magnetic resonance imaging investigation of the bone conduction implant – a pilot study at 1.5 Tesla

Abstract

PurposeThe objective of this pilot study was to investigate if an active bone conduction implant (BCI) used in an ongoing clinical study withstands magnetic resonance imaging (MRI) of 1.5 Tesla. In particular, the MRI effects on maximum power output (MPO), total harmonic distortion (THD), and demagnetization were investigated. Implant activation and image artifacts were also evaluated.Methods and materialsOne implant was placed on the head of a test person at the position corresponding to the normal position of an implanted BCI and applied with a static pressure using a bandage and scanned in a 1.5 Tesla MRI camera. Scanning was performed both with and without the implant, in three orthogonal planes, and for one spin-echo and one gradient-echo pulse sequence. Implant functionality was verified in-between the scans using an audio processor programmed to generate a sequence of tones when attached to the implant. Objective verification was also carried out by measuring MPO and THD on a skull simulator as well as retention force, before and after MRI.ResultsIt was found that the exposure of 1.5 Tesla MRI only had a minor effect on the MPO, ie, it decreased over all frequencies with an average of 1.1±2.1 dB. The THD remained unchanged above 300 Hz and was increased only at lower frequencies. The retention magnet was demagnetized by 5%. The maximum image artifacts reached a distance of 9 and 10 cm from the implant in the coronal plane for the spin-echo and the gradient-echo sequence, respectively. The test person reported no MRI induced sound from the implant.ConclusionThis pilot study indicates that the present BCI may withstand 1.5 Tesla MRI with only minor effects on its performance. No MRI induced sound was reported, but the head image was highly distorted near the implant.

<p>Robustness and lifetime of the bone conduction implant &ndash; a pilot study</p>

“…In comparison with the maximum induced torque on the transducer, which is 0.135 Nm, the retention magnet is concluded to be the main contributor to magnetically induced torque. The observed effects on the electro-acoustic performance are in line with the findings in Fredén Jansson et al,26 where the BCI was scanned in a 1.5 T MRI scanner. However, the torque of the retention magnet and that of the transducer are not assumed to constructively interact as their magnetization directions in relation to the static magnetic field of the MRI scanner are different.…”

“…In general for hearing implants, MRI may damage the device or induce a loud sound if the implant is not removed, and in the worst case, the patient may suffer from implant dislocation 25. An image artifact also occurs close to the implant, hiding part of the brain image, and for the BCI, the artifact covers a range of ~10 cm when performing brain imaging in a 1.5 T MRI scanner 26…”

Hearing Rehabilitation Using Bone Conduction Implants in Patients With Single-Sided Deafness After Vestibular Schwannoma Removal

“…BCI, bone conduction implant; SNR, signal/noise ratio evidence that we conclude the effectiveness of BCI in hearing rehabilitation for SSD. Unfortunately, in a study by Jansson, et al, 16) BCIs have wide range of artifact, about 11.5 cm from the centre of the implant in Baha attract, and 5-10 cm in Sophono. As these BCIs have the disadvantage of creating interference in MRI, also methods to solve this problem should be studied.…”

<p>Nasal sound pressure as objective verification of implant in active transcutaneous bone conduction devices</p>

“…Another application of the NSP method may be to verify the functionality after accidents, ie, if the implant has been exposed to external forces, or after performing magnetic resonance imaging (MRI). Even though the implant of the BCI should withstand MRI up to 1.5 Tesla, in this clinical study it had to be removed prior to MRI, since more testing against American Standard for Testing Materials standards is required for final approval 17…”