MRI compatibility issues in otology

Safety of active auditory implants in magnetic resonance imaging

Magnetic resonance imaging (MRI) has become the gold standard for the diagnosis of many pathologies. Using MRI in patients with auditory implants can however raise concerns due to mutual interactions between the implant and imaging device, resulting in potential patient risks. Several implant manufacturers have been working towards more MRI safe devices. Older devices are however often labelled for more stringent conditions, possibly creating confusion with patients and professionals. With this myriad of different devices that are implanted in patients for lifetimes of at least 20 years, it is crucial that both patients and professionals have a clear understanding of the safety of their devices. This work aims at providing an exhaustive overview on the MRI safety of active auditory implants. The available industry standards that are followed by manufacturers are outlined and an overview of the latest scientific developments focusing on the last five years is provided. In addition, based on the analysis of the adverse events reported to the Food and Drug Administration (FDA) and in literature within the past ten years, a systematic review of the most commonly occurring issues for patients with auditory implants in the MRI environment is provided. Results indicate that despite the release of more MRI conditional active hearing implants on the market, adverse events still occur. An extensive overview is provided on the MRI safety of active auditory implants, aiming to increase the understanding of the topic for healthcare professionals and contribute to safer scanning conditions for patients.

Cochlear Implant Magnet Dislocation: Simulations and Measurements of Force and Torque at 1.5T Magnetic Resonance Imaging

OBJECTIVES

Dislocation of the magnet inside the implanted component of a cochlear implant (CI) can be a serious risk for patients undergoing a magnetic resonance imaging (MRI) exam. CI manufacturers aim to reduce this risk either via the design of the implant magnet or magnet housing, or by advising a compression bandage and cover over the magnet. The aim of this study is to measure forces and torque on the magnet for different CI models and assess the effectiveness of the design and preventative measures on the probability of magnet dislocation.

DESIGN

Six CI models from four manufacturers covering all the current CI brands were included. Each model was positioned on a polystyrene head with compression bandage and magnet cover according to the recommendations of the manufacturer and tested for dislocation in a 1.5T whole-body MRI system. In addition, measurements of the displacement force in front of the MRI scanner and torque at the MRI scanner isocenter were obtained.

RESULTS

Chance of CI magnet dislocation was observed for two CI models. The design of the magnet or magnet housing of the other models proved sufficient to prevent displacement of the magnet. The main cause for magnet dislocation was found to be the rotational force resulting from the torque experienced inside the magnet bore, which ranges from 2.4 to 16.2 N between the models, with the displacement force being lower, ranging from 1.0 to 1.8 N.

CONCLUSIONS

In vitro testing shows that two CI models are prone to the risk of magnet dislocation. In these CI models, preparation before MRI with special compression bandage and a stiff cover are of importance. But these do not eliminate the risk of pain and dislocation requiring patient consulting before an MRI exam. Newer models show a better design resulting in a significantly reduced risk of magnet dislocation.

Rationing Rotational Magnet Cochlear Implant Technology in a Single Payer Healthcare System

INTRODUCTION

In a publicly funded health care system, fiscally responsible management of any program is required. This is especially pertinent as evolving technology and associated incremental costs, places pressure on device availability within a fixed funding envelope. The application of rotational magnet technology and associated escalating surgical wait times must be justified to patients and the single-payer system. We present a single cochlear implant center's attempt at a rationing schema for magnetic resonance compatible cochlear implantation. Contrasting approaches to rationing care are evaluated and deliberated.

METHODS

Based on a comparison of magnetic resonance imaging (MRI) rates within the general population to our cochlear implant (CI) cohort, we attempt the development of a decision-making schema that maximizes the number of patients to receive a CI while rationing the distribution of a rotational magnet technology to similarly situated individuals most likely to benefit.

RESULTS

We elect to provide rotational magnet technology to select patient cohorts. This is based on the dominant imaging needs of these populations and the probability of requiring recurrent imaging studies. We consider this an ethical approach grounded in the egalitarian principle of equality of opportunity within cohorts of patients.

CONCLUSION

Given finite resources, increasing per unit cost will unavoidably extend wait times for adult patients. Our approach does not afford similar implant devices for all patients, but rather all similarly situated individuals. Therefore, access to a scare medical resource requires program rigor and a formalized policy around candidacy for emergent technology.

Rapid, label-free detection of cerebral ischemia in rats using hyperspectral imaging

BACKGROUND

Stroke is the third most common cause of disability and the second most common cause of death worldwide. Ischemia, one of the two broad categories of stroke, is characterized by a lack of sufficient amounts of blood in order to supply an adequate amount of oxygen and nutrients. It is important to assess the part of the brain that becomes ischemic and necrotic during neurosurgery or experiments in real time. However, there is currently no effective means to achieve this goal.

NEW METHOD

We proposed a method based on hyperspectral imaging (HSI) for the real-time detection of a varied range of ischemic brain tissues in vivo or ex vivo and assessed the practical utility of a model of ischemic stroke in rats.

RESULTS

The results showed that hyperspectral images processed with a ratio of spectral reflectance at 545 and 560 nm (R545/R560) could identify early brain ischemia and accurately show regions of ischemia.

COMPARISON WITH EXISTING METHODS

We verified the area imaged by HSI using hematoxylin and eosin (HE) and 2, 3, 5-triphenyltetrazolium chloride (TTC) staining methods. This technique could precisely image the ischemic part of the brain in vivo and ex vivo.

CONCLUSIONS

These results demonstrate the practical utility of HSI for the real-time detection of cerebral ischemia in rats. By providing rapid assessment of brain tissue perfusion, HSI may help doctors recognize ischemic regions quickly and precisely during surgery as well as have great utility in the experimental process.

Comparison of MRI in pediatric cochlear implant recipients with and without retained magnet

OBJECTIVE

To report and compare medical, radiological, and audiological outcomes in pediatric cochlear implant recipients who underwent 1.5 and 3 Tesla strength MRI with and without retained magnet.

METHODS

Retrospective chart review at a tertiary care pediatric hospital and review of literature. Patients were identified via electronic medical records database search and were included if they had MRI after cochlear implant.

RESULTS

Of twelve instances of MRI in pediatric cochlear implant recipients at our institution, two minor complications and one major complication were recorded. The rate of complication was equal between patients who underwent MRI with and without retained magnet. All minor complications resulted from MRI with retained magnet whereas the only major complication resulted from magnet removal. Two novel complications are reported, including: magnet removal resulting in silastic tear necessitating reimplantation and magnet dislocation with spontaneous reduction. Magnet removal significantly decreased the size of artifact, but did not alter the diagnostic utility of the MRI. While audiological measures varied chronologically from MRI scans, they did not appear to be appreciably altered by MRI.

CONCLUSION

MRI with and without magnet retention appear to carry risks of both major and minor complications. For the regions of interest for each scan, MRI quality was not appreciably altered by magnet status. Audiological measures appear unaffected by magnet status during MRI however, this may reflect natural variation.

Significant Artifact Reduction at 1.5T and 3T MRI by the Use of a Cochlear Implant with Removable Magnet: An Experimental Human Cadaver Study

Objective

Cochlear implants (CIs) are standard treatment for postlingually deafened individuals and prelingually deafened children. This human cadaver study evaluated diagnostic usefulness, image quality and artifacts in 1.5T and 3T magnetic resonance (MR) brain scans after CI with a removable magnet.

Methods

Three criteria (diagnostic usefulness, image quality, artifacts) were assessed at 1.5T and 3T in five cadaver heads with CI. The brain magnetic resonance scans were performed with and without the magnet in situ. The criteria were analyzed by two blinded neuroradiologists, with focus on image distortion and limitation of the diagnostic value of the acquired MR images.

Results

MR images with the magnet in situ were all compromised by artifacts caused by the CI. After removal of the magnet, MR scans showed an unequivocal artifact reduction with significant improvement of the image quality and diagnostic usefulness, both at 1.5T and 3T. Visibility of the brain stem, cerebellopontine angle, and parieto-occipital lobe ipsilateral to the CI increased significantly after magnet removal.

Conclusions

The results indicate the possible advantages for 1.5T and 3T MR scanning of the brain in CI carriers with removable magnets. Our findings support use of CIs with removable magnets, especially in patients with chronic intracranial pathologies.

MRI Information for Commonly Used Otologic Implants

Objective

To review information on magnetic resonance imaging (MRI) issues for commonly used otologic implants.

Data Sources

Manufacturing companies, National Library of Medicine’s online database, and an additional online database ( www.MRIsafety.com ).

Review Methods

A literature review of the National Library of Medicine’s online database with focus on MRI issues for otologic implants was performed. The MRI information on implants provided by manufacturers was reviewed.

Results

Baha and Ponto Pro osseointegrated implants’ abutment and fixture and the implanted magnet of the Sophono Alpha 1 and 2 abutment-free systems are approved for 3-Tesla magnetic resonance (MR) systems. The external processors of these devices are MR Unsafe. Of the implants tested, middle ear ossicular prostheses, including stapes prostheses, except for the 1987 McGee prosthesis, are MR Conditional for 1.5-Tesla (and many are approved for 3-Tesla) MR systems. Cochlear implants with removable magnets are approved for patients undergoing MRI at 1.5 Tesla after magnet removal. The MED-EL PULSAR, SONATA, CONCERT, and CONCERT PIN cochlear implants can be used in patients undergoing MRI at 1.5 Tesla with application of a protective bandage. The MED-EL COMBI 40+ can be used in 0.2-Tesla MR systems. Implants made from nonmagnetic and nonconducting materials are MR Safe.

Conclusion

Knowledge of MRI guidelines for commonly used otologic implants is important. Guidelines on MRI issues approved by the US Food and Drug Administration are not always the same compared with other parts of the world.

Implications for Practice

This monograph provides a current reference for physicians on MRI issues for commonly used otologic implants.

Pediatric cochlear implantation: expanding applications and outcomes

Cochlear implantation is a revolutionary yet time-sensitive treatment for deaf children that must be performed within a critical window of time, in early life, for a congenitally deafened child to receive maximum benefit. Potential candidates should therefore be referred for evaluation early. Primary reasons for delay of cochlear implantation include slow referrals for care, parental delays, and payer delays. It is vital that all newborn children undergo hearing screening to identify deaf children at birth, and for parents, health care providers, and health care payers to be educated about the indications, important benefits, and reasonable risks of cochlear implantation for deaf children.

[Guidelines for the performance of MRI in patients with cochlear implants]

The number of patients with cochlear implant increases each year. Most of these patients may undergo MR imaging up to 1.5 Tesla, based on safety recommendations from each of the manufacturers. All external components should be removed for the examination. For three manufacturers providing about 85 % of all implanted devices in Europe, the internal components may be left in place and covered by an external bandage. Strict protocol guidelines must be implemented, especially head positioning in the magnet and within 30 cm from the bore opening. A single manufacturer, providing about 15 % of implanted devices, recommends surgical removal of the internal magnet prior to MR imaging.

[Radiological diagnosis of the paranasal sinuses]

Although diseases of the paranasal sinuses have a relatively homogeneous clinical presentation, their causes can vary considerably. Radiological imaging only became relevant in paranasal sinus diagnostics following the introduction of cross-sectional imaging. In addition to technical details on imaging procedures and the individual criteria of the different modalities, anatomic details and congenital variations are presented. Particularly in acute inflammatory diseases as well as traumatic lesions, imaging is essential in preoperative planning and postoperative control. The article gives a detailed description of options in radiologic imaging of the paranasal sinuses.