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MRI Trends and the MED-EL SYNCHRONY Cochlear Implant

Darla Franz

August 17, 2015
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Interview with Darla Franz, Vice President of Education, MED-EL Corporation, North America


Carolyn Smaka: MED-EL’s SYNCHRONY cochlear implant is the first and only cochlear implant approved for 3.0 Tesla (T) MRI without magnet removal. Is MRI something that a cochlear implant candidate should be concerned about, especially if he or she is healthy?

Darla Franz:  Yes. Cochlear implant (CI) candidates of any age need to consider the fact that they will likely need an MRI at some point in their lifetime.

When cochlear implants first became available commercially in the 1980s, MRI was not a widely used diagnostic tool like it is today.  Since then, MRI technology has come a long way such that it’s now becoming one of the top diagnostic and monitoring tools for many conditions, including diseases of aging.  Most people will have an MRI at some point in their lifetime.  To paraphrase a CI surgeon who recently implanted the SYNCRHONY, it’s not a matter of “if” someone will need an MRI in his or her lifetime; it’s a matter of “when.”  We are no longer talking about a small subset of the population who will need MRIs; rather, we are talking about the majority of people.  And, the number is predicted to continue to grow in the future.

For some conditions, frequent MRIs may be required, such as to monitor certain cancers or multiple sclerosis, for example. 

In addition to the upward trend in MRI usage, the population is aging and people are living longer.   There is no upper age limit for cochlear implantation and we are seeing more CIs in the older adult population.  As you age, there is a greater likelihood that you will face not only significant hearing loss, but also conditions that warrant an MRI. 

The bottom line is that the issue of cochlear implants and MRI is now more important than ever, and should be considered by every cochlear implant candidate today.

Carolyn:  So, what exactly are the issues with CIs and MRIs?

Darla:  MRI machines are classified according to the strength of their magnets.  The stronger the magnet, the higher the resolution of the scan, and also the stronger the magnetic force.  The MRI magnet interacting with the magnet in cochlear implants is the main issue.  It doesn’t matter which part of the body is being scanned; even if the patient needs an MRI of the knee, the internal cochlear implant magnet can be affected.

When it comes to medical devices and MRI, there are certain regulatory terms that are important: “MR Safe” and “MR Conditional.” A device that’s classified as MR Safe can go into an MRI scanner with no precautions.  It doesn’t cause any negative problem with the scan.  MR Conditional means that the device is safe with MRI provided you follow specific conditions. SYNCHRONY is classified as MR Conditional, meaning that certain conditions must be met to ensure safety, such as the patient being positioned correctly in the MRI scanner.  The complete list of conditions is on our website for all of our implants.

Carolyn:  All MED-EL implants are MR Conditional without magnet removal?

Darla:  In June 2013, MED-EL received FDA approval for the PULSARSONATA, and CONCERT implants to be scanned at 1.5T without magnet removal.  The new SYNCHRONY implant is approved for both 1.5T and 3.0T MRI without magnet removal.

Back in 2001, our COMBI 40+ cochlear implant was the first cochlear implant to be FDA approved for MRI with the magnet in place – this was for the 0.2T MRI scanners that were in use at that time.

These tended to be “open” MRI machines that were often used to obtain imaging in people who were either claustrophobic or obese and could not tolerate a traditional machine.  At that time, we were able to fix the magnet inside our COMBI 40+ implant in such a way that prevented the magnet from moving when the patient was correctly positioned in one of those open scanners.

Over the years, MRI strength and image resolution have increased.  First, 1.0T magnets were introduced, and then the 1.5T magnets came out.  We now see the 3.0T MRI in use.  The 1.5T MRI is most commonly used in the United States right now.  But, we expect that usage of the 3.0T MRIs will increase due to the higher resolution of the scans and through the replacement of older 1.5T technology.

Carolyn: Before the MED-EL COMBI 40+, did CI magnets always need to be removed for MRI?

Darla:  Some implants had removable magnets, and for those, yes.  Or physicians just used other diagnostic tools like CT scans if they could.  And to this day, all of our competitors have implants with removable magnets; they are not FDA approved for MRI scanning with the magnet in place with 1.5T MRI, and they are not FDA approved for 3.0T MRI under any circumstances, even with the magnet removed.  Again, this is regardless of what part of the body receives the MRI.

Carolyn:  How does the removable magnet technology in CIs work?

Darla:  Removing the CI magnet for an MRI, and subsequently replacing a CI magnet after MRI, requires surgery.  So, two procedures are necessary – one pre-MRI and one post-MRI.  Often these procedures need insurance preauthorization, so there may be some built-in waiting time while that is obtained.

Although it sounds straightforward to just remove the magnet, have an MRI, and then put it back in, it isn’t really that simple.  Logistically, the surgical suite may be in a different location from the MRI scanner.  The appointments for the surgery and MRI may be on different days.  So, after magnet removal, the surgical wound needs to be closed and bandaged so that the patient can leave the operating room or even the hospital to complete their MRI scan.  Following the MRI, the surgeon goes back in and puts a new magnet in place. You can’t use the old magnet; a new, sterile magnet must be purchased, which may also require insurance preauthorization.  As you know, insurance authorization can take days or weeks.  The incision must heal before the coil can be placed over the skin on the outside and the wearer can hear with the CI again.   Aside from the pain and discomfort of the surgery, there’s also the risk of infection associated with any procedure. If you have a medical issue that requires you to have frequent MRIs, or you are a bilateral CI wearer, in which case both magnets need to be removed, it becomes clear that repeated removal of the internal magnet just isn’t a good option if it can be avoided. There will be times that it is unavoidable. 

Carolyn: What makes the SYNCHRONY design unique so that it can undergo a 3.0T MRI without requiring magnet removal?

Darla:  In the development of SYNCHRONY, our engineers started thinking about: “How can we create a magnet that could stay in the implant, wouldn’t have to be removed, and would still be able to be scanned with this newer 3.0 Tesla MRI technology?” And they hit upon the idea of a diametric magnet.  It’s a revolutionary design – now patented by MED-EL – that hasn’t, to our knowledge, been used in any other implantable devices.

Up until now, all CIs used an axial magnet.  These are tiny discs shaped like a penny (but smaller).  One side of the disc, like the “heads” side of a penny, has a magnet pole that’s one direction, either positive or negative, and the other “tails” side of the disc has the opposite pole.  When the magnet sits against the head in the properly implanted position, the disc is laying down flat.

When you put an axial magnet inside of another strong magnetic field like an MRI, the polarized side of the magnet wants to line up with the larger magnet that’s outside. That causes a lifting motion we call “torque.”  The CI magnet tends to tilt up, away from the surface of the head.  It can be uncomfortable or cause pain even if the magnet tilts a little.  We know this from published literature where patients had CI magnets that were intended to be removed for MRI, but who underwent MRI with the magnets in place (e.g., Kim et al., 2015).  Keep in mind that FDA requirements for medical devices and MRI do not apply to other countries in the world.

In designing SYNCHRONY, MED-EL’s engineers theorized that if they could change the way the magnet is polarized so that it doesn’t torque, that might solve the problem.  In a diametric magnet, the two magnetic poles of the magnet are located on the curved surface area opposite to each other. One magnetic pole is polarized one way, and the other one is polarized the other way.  Think about a clock: from noon to 6:00 is polarized one direction, and from 6:00 back to 12:00 is polarized the other direction - all along the edge of the disc.

The SYNCHRONY magnet sits within a titanium housing, and it can rotate freely within that case.  When a larger magnetic field is applied such as MRI, the magnet inside of the titanium capsule wants to align, and now it can simply turn - like a needle turns in a compass -  into a position where the magnetic forces are neutral.

Then, once the patient puts their CI listening coil back on their head, the magnet rotates back into the place it needs to be to work with the external audio processor/coil.  The implant magnet can rotate and adjust to that external field in order to essentially eliminate torque. 

Of course, we considered other things besides torque in the development of SYNCHRONY, such as unintended stimulation, depolarization of the implant magnet, and heating of the metal components,; all of these issues are managed by properly positioning the patient in the MRI scanner. 

Lastly, we had to consider artifact.  Artifacts are caused by metals in the implant and mostly by CI magnets.  In the area immediately around the implant the artifact creates a void, or darkened area, on the scan.  This is not an issue with an MRI scan on any other part of the body or even with many MRI scans of the head.  However, in the rare case that the area in the immediate vicinity of the implant needs to be scanned, the SYNCHRONY magnet can be removed.

Carolyn: It covers all bases, so to speak.

Darla: Right.  We now have a cochlear implant where the magnet can be scanned in place with up to a 3.0T MRI, and can also be removed if needed.  In fact, even the removal process has been improved over other CIs with removable magnets. 

There have been issues with other CIs where removable magnets have inadvertently worked their way out of the silicone pocket they sit in, even without being put in an MRI scanner.  So having a removable magnet that can’t be moved except deliberately was part of our design plan for SYNCHRONY.

If you look at the SYNCHRONY magnet from the side in cross-section, you will see it is shaped almost like a little hourglass.  It’s a flat disc, but it has a bit of a conical shape around the edges and the magnet only inserts into the implant from underneath, so the conical shape allows it to snap into place.  This enables surgeons to remove and insert it using special instruments , and yet keeps the magnet as safe and stable as possible, as it can only come out from the underside of the implant (the side against the head).

The diametric design – coupled with the conical shape and the insertion and removal from underneath the implant – really adds to the safety.

CAROLYN:  In addition to the fact that SYNCHRONY is approved for MRI scans up to 3.0 T without magnet removal, what other benefits does it offer?

Darla:  The SYNCHRONY implant offers benefits for all cochlear implant users.  The approval for MRI scans up to 3.0 Tesla without magnet removal is an added feature for an implant that is already state-of-the-art.

The SYNCHRONY implant has what was call the i100 electronics platform, which has the ability to perform different kinds of coding, including the ability to fire more than one electrode at the same time. 

We’ve recently introduced some new coding strategies that depend on that platform, such as FS4p.  FS4p uses parallel stimulation, meaning stimulation of more than one channel at the same time, and is also back compatible to previous MED-EL implants with that platform. This is just one example of future-ready technology in the electronics platform.  The internal electronics are built to have a number of capabilities that we can release over time as the externals or coding evolve – the goal being that the implant remains cutting edge for as long as possible – and the end-user will be able to access the latest technology without the need for a new implant.

SYNCHRONY is also the smallest and lightest implant available today. This can be particularly important when implanting babies and young children.

MED-EL is also the only company that different soft, flexible electrode configurations that are sized to fit different cochleas.  We can tell the size of the cochlea from pre-op imaging, and there is a calculation the surgeon can do to choose an electrode array that is sized to fit that individual cochlea. There are two primary lengths that we use, but there are more available for special cases such as a Mondini malformation.  We can also provide the surgeon with a variety of implants with different electrode lengths.  That way, the surgeon can choose the length that is best for the individual patient during the surgery.

Carolyn: Why is the right length of the CI electrode array important?

Darla: One of MED-EL’s primary philosophies across all of our implants is what we call “complete cochlear coverage.”  This refers to using an electrode array that covers the entire cochlea, including the apex where low frequency sounds are located.   It’s important to us to stimulate the full spectrum of sound.

Electrode arrays that only go halfway or two thirds of the way into the cochlea also send low frequency information –  to the wrong place in the cochlea.  So the patient perceives the sound as lower than the other pitches they’re getting through the implant, but it’s not perceived as the correct pitch – in fact, it can actually be up to a several octave shift in some cases.  You will hear patients who say, “When my cochlear implant was turned on, voices sounded like Mickey Mouse, or a cartoon character.”  That is because they’re listening to a frequency shift. 

Eventually the brain works around that and the gap closes some, although there’s some evidence that it never closes completely.  Our philosophy is to not waste the brain’s effort and the patient’s time waiting for that to happen – instead, why not just deliver the stimulation as close as possible to where it should be?  Today, many people with cochlear implants wear a hearing aid on the non-implanted side. It is now more important than ever to have the correct spectrum of sound and the right pitch match, so that when we send a 200 Hz tone into the cochlear implant, we’re sending it as close as we can possibly get to the 200 Hz location in the cochlea. If the patient can also hear 200 Hz with their hearing aid on the other ear, ideally it should all sound good together.

Carolyn:  Darla, this has been a very informative conversation.  Thanks for your time and wishing MED-EL much success with the new SYNCHRONY cochlear implant.

References

Kim, B.G., Kim, J.W., Park, J.J., Kim, S.H., Kim, H.N., Choi, J.Y. (2015).  Adverse events and discomfort during magnetic resonance imaging in cochlear implant recipients. JAMA Otolaryngol Head Neck Surg. 141(1):45-52. doi:10.1001/jamaoto.2014.2926 

For more information, visit http://www.medel.com/us/ or the MED-EL Expo Page on AudiologyOnline.

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Darla Franz

Darla Franz is Vice President of Education, MED-EL Corporation, North America.