Karl-Johan Fredén Jansson

The Bone Conduction Implant-First Implantation, Surgical and Audiologic Aspects.

Objective To report on preoperative assessment, surgery, and audiologic outcome of the first patient implanted with the bone conduction implant (BCI). Background The BCI is a bone conduction hearing device with an intact skin solution where the transducer is implanted close to the ear canal opening. By avoiding a percutaneous screw attachment to the skull, the BCI is anticipated to reduce complications associated with the Bone-Anchored Hearing Aid (BAHA) solution. Methods The first patient to receive a BCI was a 42-year-old woman with a unilateral mixed hearing loss due to tympanosclerosis. Preoperative and postoperative cone beam computed tomography and a virtual planning tool for 3D reconstruction were used to optimize and control the position of the BCI in the mastoid. The transducer was placed in a 5-mm deep seating in the mastoid and secured with a titanium bar. Free field tone and speech audiometry were conducted to evaluate the audiologic outcome at baseline (1 month postoperatively) and 1 month after baseline. Results The BCI was placed in the position according to the preoperative 3D planning. On average, the tone thresholds improved by 30 dB, speech reception thresholds by 25.5 dB and speech signal-to-noise ratio by 9.7 dB. The surgical procedure was considered simple and safe. Conclusion The BCI can be implanted by a safe and easy surgical procedure. 3D preoperative planning can be helpful to optimize the BCI position. The BCI is a realistic alternative to the BAHA.

The bone conduction implant: Clinical results of the first six patients

Abstract Objective: To investigate audiological and quality of life outcomes for a new active transcutaneous device, called the bone conduction implant (BCI), where the transducer is implanted under intact skin. Design: A clinical study with sound field audiometry and questionnaires at six-month follow-up was conducted with a bone-anchored hearing aid on a softband as reference device. Study sample: Six patients (age 18–67 years) with mild-to-moderate conductive or mixed hearing loss. Results: The surgical procedure was found uneventful with no adverse events. The first hypothesis that BCI had a statistically significant improvement over the unaided condition was proven by a pure-tone-average improvement of 31.0 dB, a speech recognition threshold improvement in quiet (27.0 dB), and a speech recognition score improvement in noise (51.2 %). At speech levels, the signal-to-noise ratio threshold for BCI was − 5.5 dB. All BCI results were better than, or similar to the reference device results, and the APHAB and GBI questionnaires scores showed statistically significant improvements versus the unaided situation, supporting the second and third hypotheses. Conclusions: The BCI provides significant hearing rehabilitation for patients with mild-to-moderate conductive or mixed hearing impairments, and can be easily and safely implanted under intact skin.

Technical design of a new bone conduction implant (BCI) system

Abstract Objective: The objective of this study is to describe the technical design and verify the technical performance of a new bone conduction implant (BCI) system. Design: The BCI consists of an external audio processor and an implanted unit called the bridging bone conductor. These two units use an inductive link to communicate with each other through the intact skin in order to drive an implanted transducer. Study sample: In this study, the design of the full BCI system has been described and verified on a skull simulator and on real patients. Results: It was found that the maximum output force (peak 107 dB re 1 μN) of the BCI is robust for skin thickness range of 2–8 mm and that the total harmonic distortion is below 8% in the speech frequency range for 70 dB input sound pressure level. The current consumption is 7.5 mA, which corresponds to 5–7 days use with a single battery. Conclusions: This study shows that the BCI is a robust design that gives a sufficiently high output and an excellent sound quality for the hearing rehabilitation of indicated patients.

Electro-acoustic performance of the new bone vibrator Radioear B81: A comparison with the conventional Radioear B71

Abstract Objective: The objective is to evaluate the electro-acoustic performance of a new audiometric bone vibrator, the B81 from Radioear Corporation, USA. Comparison will be made with the widely used B71 which has well-known limitations at low frequencies. Design: The B81 is based on the balanced electromagnetic separation transducer (BEST) principle where static forces are counterbalanced so that nonlinear distortion forces are reduced and maximum hearing levels can be increased. Study sample: Maximum hearing level, total harmonic distortion (THD), frequency response, and electrical impedance were measured for six devices of each bone vibrator type on an artificial mastoid. Results: It was found that B81 reaches 10.7–22.0 dB higher maximum (@ THD = 6% or Vin = 6 VRMS) hearing levels than B71 for frequencies below 1500 Hz, and had significantly lower THD up to 1000 Hz. There was no statistically significant difference between their frequency response, except a deviation at the mid frequencies (α = 0.01) where B81 was more efficient and the electrical impedances were practically the same. Conclusions: In general, B81 had an improved electro-acoustic performance compared to B71 and is compatible with same audiometers. In particular, B81 allows for sensorineural hearing loss to be measured at considerably higher hearing levels than with B71 below 1500 Hz.

MRI Induced Torque and Demagnetization in Retention Magnets for a Bone Conduction Implant

Performing magnetic resonance imaging (MRI) examinations in patients who use implantable medical devices involve safety risks both for the patient and the implant. Hearing implants often use two permanent magnets, one implanted and one external, for the retention of the external transmitter coil to the implanted receiver coil to achieve an optimal signal transmission. The implanted magnet is subjected to both demagnetization and torque, magnetically induced by the MRI scanner. In this paper, demagnetization and a comparison between measured and simulated induced torque is studied for the retention magnet used in a bone conduction implant (BCI) system. The torque was measured and simulated in a uniform static magnetic field of 1.5 T. The magnetic field was generated by a dipole electromagnet and permanent magnets with two different types of coercive fields were tested. Demagnetization and maximum torque for the high coercive field magnets was 7.7% ± 2.5% and 0.20 ± 0.01 Nm, respectively and 71.4% ± 19.1% and 0.18 ± 0.01 Nm for the low coercive field magnets, respectively. The simulated maximum torque was 0.34 Nm, deviating from the measured torque in terms of amplitude, mainly related to an insufficient magnet model. The BCI implant with high coercive field magnets is believed to be magnetic resonance (MR) conditional up to 1.5 T if a compression band is used around the skull to fix the implant. This is not approved and requires further investigations, and if removal of the implant is needed, the surgical operation is expected to be simple.

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

Purpose The 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 materials One 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. Results It 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. Conclusion This 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.

Touch and Hearing Mediate Osseoperception

Osseoperception is the sensation arising from the mechanical stimulation of a bone-anchored prosthesis. Here we show that not only touch, but also hearing is involved in this phenomenon. Using mechanical vibrations ranging from 0.1 to 6 kHz, we performed four psychophysical measures (perception threshold, sensation discrimination, frequency discrimination and reaction time) on 12 upper and lower limb amputees and found that subjects: consistently reported perceiving a sound when the stimulus was delivered at frequencies equal to or above 400 Hz; were able to discriminate frequency differences between stimuli delivered at high stimulation frequencies (~1500 Hz); improved their reaction time for bimodal stimuli (i.e. when both vibration and sound were perceived). Our results demonstrate that osseoperception is a multisensory perception, which can explain the improved environment perception of bone-anchored prosthesis users. This phenomenon might be exploited in novel prosthetic devices to enhance their control, thus ultimately improving the amputees’ quality of life.

Evaluation of bone tissue formation in a flat surface attachment of a Bone Conduction Implant - A pilot study in a sheep model

The bone conduction implant (BCI) is a new bone conduction hearing device implanted under intact skin. The transducer has a flat direct contact with the mastoid part of the temporal bone, and no screws are used. The sound signal is transmitted from the external audio processor to the implant by means of magnetic induction. In this study, osseointegration of a flat passive BCI transducer dummy in sheep skulls was assessed using quantitative and qualitative histology as well as cone beam computed tomography (CBCT) and computed tomography (CT). The histology results were also related to the mechanical properties of the bone-to-implant interface. Eight months after the surgical implantation, histology sections of the bone close to the implant showed bone remodeling, compact bone and osseointegration. The histological findings corresponded well to the mechanical measurements indicating stiffer bone close to the implant and unaffected skull vibration transmission. Neither CBCT nor CT had enough resolution to visualize the bone-to-implant interface in detail. In this study, using an animal model, it is shown that a flat implant in contact with bone can be a feasible method for efficient vibration transmission to the skull bone.

VEMP using a new low-frequency bone conduction transducer

Objective A new prototype bone conduction (BC) transducer B250, with an emphasized low-frequency response, is evaluated in vestibular evoked myogenic potential (VEMP) investigations. The aim was to compare cervical (cVEMP) and ocular (oVEMP) responses using tone bursts at 250 and 500 Hz with BC stimulation using the B250 and the conventional B81 transducer and by using air conduction (AC) stimulation. Methods Three normal subjects were investigated in a pilot study. BC stimulation was applied to the mastoids in cVEMP, and both mastoid and forehead in oVEMP investigations. Results BC stimulation was found to reach VEMP thresholds at considerably lower hearing levels than in AC stimulation (30–40 dB lower oVEMP threshold at 250 Hz). Three or more cVEMP and oVEMP responses at consecutive 5 dB increasing mastoid stimulation levels were only obtained in all subjects using the B250 transducer at 250 Hz. Similar BC thresholds were obtained for both ipsilateral and contralateral mastoid stimulation. Forehead stimulation, if needed, may require a more powerful vibration output. Conclusion Viable VEMP responses can be obtained at a considerably lower hearing level with BC stimulation than by AC stimulation. The cVEMP and oVEMP responses were similar when measured on one side and with the B250 attached to both ipsilateral and contralateral mastoids.

Direct bone conduction stimulation: Ipsilateral effect of different transducer attachments in active transcutaneous devices

ABSTRACT Active transcutaneous bone conduction devices, where the transducer is implanted, are used for rehabilitation of hearing impaired patients by directly stimulating the skull bone. The transducer and the way it is attached to the bone play a central role in the design of such devices. The actual effect of varying the contact to bone has not been addressed yet. The aim of this study is therefore to compare how different attachment methods of the transducer to the bone for direct stimulation affect the ear canal sound pressure and vibration transmission to the ipsilateral cochlea. Three different attachments to the bone were tested: (A) via a flat small‐sized surface, (B) via a flat wide surface and (C) via two separated screws. Measurements were done on four human heads on both sides. The attachments were compared in terms of induced cochlear promontory velocity, measured by a laser Doppler vibrometer, and ear canal sound pressure, measured by a low noise microphone. A swept sine stimulus was used in the frequency range 0.1–10 kHz. On an average level, the attachment method seems to affect the transmission mainly at frequencies above 5 kHz. Furthermore, the results suggest that a smaller contact surface might perform better in terms of transmission of vibrations at mid and high frequencies. However, when considering the whole frequency range, average results from the different attachment techniques are comparable. HighlightsDifferent transducer attachments to skull bone affect vibrations transmission to the cochlea in a frequency‐dependent way.Increasing the size of the contact surface leads to a generally decreased transmission sensitivity above 5 kHz.Further investigation on the effect of the attachment may lead to improved design of direct drive bone conduction devices.