Magnetic resonance imaging (MRI) is a type of medical imaging with characteristics that make it especially suitable for certain diagnostic applications. While x-rays and computed tomography (CT) are terrific for acquiring images of hard bodily tissues like bones, diagnostic MRI scanning offers superior image quality for soft tissues, including the joints and the brain.
Sometimes diagnostic MRI scanning is chosen as a medical imaging modality for children because it uses magnetic fields rather than ionizing radiation to create images. While MRI takes longer than a CT scan, and requires the patient to remain motionless, children are particularly vulnerable to the effects of ionizing radiation. This may cause some pediatric radiology specialists to opt for MRI scanning with some children in order to avoid exposing them to ionizing radiation.
Worldwide, around 60 million MRI scans are performed every year, but until recently, patients with pacemakers or other implantable cardiac devices have been advised not to have MRIs because the magnetic fields involved in MRI scanning can interfere with proper functioning of these devices. In fact, around 200,000 patients in the US are denied MRI scans every year due to having implantable cardiac devices.
Around 1.5 million Americans have implanted cardiac devices, and anywhere from half to three-quarters of these people will eventually have a condition that indicates the need for MRI scanning. This is particularly true of older patients. After age 65, the need for MRI scanning doubles, and 80% of pacemakers are implanted in people over age 65. Does this mean the person with an implantable defibrillator or pacemaker has to forego MRI scanning permanently? Not necessarily.
Why People With Defibrillators Are Advised Against MRI
Implantable defibrillators specifically designed to be MRI-friendly have recently started being used in the US. With older defibrillators, the magnetic energy from MRI scanning could interfere with the electrical signals the defibrillators delivered to the heart. This could do things like reset the defibrillator to factory default conditions or otherwise prevent it from correctly monitoring and treating abnormal heart rhythms. The new, MRI-friendly devices, however, have a combination of hardware, software, and programming changes that keep them from malfunctioning during MRI scanning. Soon after approval of these devices, doctors began implanting them in patients in Missouri, Colorado and elsewhere.
The New MRI-Friendly Implantable Defibrillator
Implantable defibrillators are life-saving devices, estimated to have saved around 70,000 lives over just the past five years. They detect abnormal heart rhythms and then deliver a shock to the heart that returns it to a normal rhythm. Doctors who implant defibrillators are excited about these new models and expect them to eventually become the standard. With the new implantable devices, patients who develop a condition for which MRI is indicated will no longer have to forego MRI scanning and can be confident their implantable device will continue to work properly afterward.
Other challenges with designing the new MRI-friendly defibrillators included maintaining the same size and general shape as older implantable devices while providing the same longevity and proper functioning. The new devices are coupled with a specific type of electrical lead that has itself been tested for safety in an MRI environment. It’s important for anyone with a defibrillator or other implantable cardiac device (like a pacemaker) to know when their device was made, and whether it is MRI-friendly or not to avoid safety issues.
Why MRI-Friendly Defibrillators Represent an Important Medical Advance
The very patients who need implantable defibrillators are often older adults who have additional medical conditions – conditions that may indicate diagnostic MRI scanning. Until now, the risk of a defibrillator malfunctioning has made MRI off limits to these patients except when extensive precautions are taken.
Some major medical centers, like Johns Hopkins Hospital, developed scanning protocols that allowed some people with implantable defibrillators to safely undergo MRI scanning. However, before the MRI, patients would have to have their device fully tested, and then reprogrammed in an “MRI-safe” setting before even going into the MRI room. Additionally, an EKG of the patient would be continuously monitored by a doctor or nurse with additional specialty training in MRI safety and cardiac device management. After the MRI, the device would have to be retested to ensure it had not been damaged before being restored to the settings prescribed for that patient.
Not everyone with heart problems is eligible for the MRI-friendly implantable devices, and those who do have them will still need to inform radiologists or other doctors of the presence of the defibrillator before MRI scans take place. But in general, these new devices open up diagnostic MRI scanning as a possibility for many people who could not have it done before.
Other Types of Medical Imaging and Defibrillators
Several years ago, the US Food and Drug Administration (FDA) issued warnings about dangers of CT scans for people with pacemakers or defibrillators. The cautions related to fears that the ionizing radiation used in CT scans could cause these devices to malfunction, possibly causing defibrillators to deliver unintended shocks or causing pacemakers to change the heart’s pumping rate.
However, radiologists who have collectively done hundreds of thousands of CT scans without issues questioned the need for the FDA warning. In a more recent study published in the Journal of the American College of Cardiology over 500 people with implantable cardiac devices had CT scans, and no cases were reported of changes in heart pumping rates, unnecessary shocks from defibrillators, or the need for devices to be reset. This study, along with the new MRI-friendly defibrillators should make diagnostic medical imaging more useful in these populations.
Successful MRI Scanning Requires Understanding of Many Medical Specialties
MRI scanning and other medical imaging modalities require radiologists, like SteleRAD’s Eric L. Alboucrek, DO, Michael DiGiorgio, MD, and Carl Raboi, MD to understand many other medical specialties and how they affect medical imaging. Knowing information like whether a person has an implantable defibrillator and when it was manufactured can help radiologists make the safest choices that will produce the highest quality medical images. If you would like to learn more about how the Board-certified radiologist owner-operators of SteleRAD can assist your hospital, imaging center, or medical practice, we encourage you to call 954-358-5250 or contact us online at any time.