The last couple of decades have seen unimaginable changes, fueled by technology and innovation in every area. The medical device sector is no exception.
Magnetic Resonance Imaging (MRI) is rising in popularity and expanding into new areas of medicine. There are plenty of reasons behind this increase, including the growing elderly population and easier access to information regarding medical procedures. MRI allows physicians to formulate early and accurate diagnoses, which - from a patients' perspective - spares a lot of stress and shortens hospitalization time.
Although MRI technology is very beneficial, it is not entirely free of disadvantages and risks. One issue is a potential threat to patients wearing implantable devices, such as pacemakers. In individuals with pacemakers, there are implanted metal leads touching the heart surface, the lead wires of the implants can act as antennas and pick up the electric field generated by the RF coil. This results in the induced current traveling along the length of the device that will dissipate as heat where it is coupled to tissue. The combination of critically sensitive tissues and high heat makes this interaction the most significant risk for patient safety. Hence, there arises a need to design effective techniques that can minimize RF heating induced during an MRI. The technique of shielding has been proven to reduce RF-induced heating.
Dr. Krishna Singhal, an expert in MRI safety, has analyzed shielded implantable leads for MRI compatibility. These implantable leads are compliant with ISO 10974 standard for MRI characterization. Dr. Krishna's contribution enables many patients, especially those suffering from chronic cardiac conditions, to safely undergo MRI scans. It also helps doctors to diagnose the root causes of a given illness more effectively and efficiently.
What Are Implantable Leads?
There have been significant advancements in implantable devices in the last decade. Implantable cardioverter-defibrillators (ICDs), pacemakers, and neuro-stimulators have seen improvements in both design and development. At the same time, there has been a significant rise in the number of patients opting for such implants. The implantable leads are the electrodes found at the ends of these devices, which are used to attach the device to the organ itself. These refer to the lead wires from the IPG to the position on the surface of or inside the heart.
How does the MRI environment affect the implanted device?
The MR environment involves a strong static and time-varying magnetic field (static, gradient, and RF) each of which carries specific safety concerns. The radiofrequency energy used during the MRI scan could lead to heating of the body. The potential for heating is greater during long MRI examinations. Dr. Singhal's work focuses on the analysis of shielding technique for the reduction of RF-induced heating of electrodes during MRI. "Shielded leads have been developed as a method to reduce RF-heating responsible for temperature rise at the electrodes. However, there is no fundamental understanding of how shielding works, what is the physics behind it, and the design equations associated with it.", he says. "The purpose of this work was to provide a qualitative and quantitative understanding of how a conducting metallic shield over a lead will reduce RF heating at the electrode during MRI scans." Now with the information provided by Dr. Singhal's work, we can expect the development of shielded lead wires which can be MRI safe.
What is an "MRI Safe" Device?
FDA and other regulatory agencies assess MRI safety before approving a medical device. These implantable medical devices fall into one of three categories:
● MR Safe: Non-conductive and non-magnetic medical devices fall into this category. These qualities ensure that the MRI environment does not affect the function of the implanted device.
● MR Conditional: This category of medical device can safely undergo an MRI scan under controlled conditions. These devices may or may not be electrically conductive, however, they are safe to use under certain conditions or within specific parameters.
● MR Unsafe: Medical devices in this group are dangerous in an MRI environment.
Why is MRI Safety Significant?
The recent increase in patients opting for implants in the US has been phenomenal. The research suggests that the trend will likely continue, and the projected statistics are quite interesting.
● The number of joint reconstruction and spinal cord implant surgeries performed in the UK, Germany, France, Spain, and Italy is expected to rise from 2.8 million in 2018 to more than 3.5 million in 2023.
● In these countries, 19% of the population over the age of 65 has orthopedic implants. This number is expected to rise above 30% in 2021.
● Between 2005 and 2030, hip and knee replacement surgeries are expected to increase by 175% and 673%, respectively.
● The number of revision surgeries for total knee and total hip replacements will keep increasing until 2030.
● At this time, 4% of the population over 65 years of age has a cardiac implant, and this figure is expected to rise to 12% by 2025
● In the US, 17% of the population over 65 has a joint or spinal implant, and 10.4% of the same people have a cardiac implant. It is expected that these figures will rise respectively.
The clinical need for an MRI scan among patients with implantable devices is significant, thus minimizing threats during the examination seems imperative. In addition, MRI safety concerns may prevent patients with various implantable devices from receiving necessary treatment if they require MRI scans, such as cancer patients. Other options, such as CT or X-Ray scans, are also less than ideal and are often less effective than MRI. These factors are what inspired Dr. Singhal to pursue his research in medical device safety. Dr. Singhal's expertise and interests will be essential in the medical device safety field, as evolving health care continues to pose new challenges, despite the advancements and innovation of technology. Safe medical devices and techniques will, without a doubt, play a vital role in achieving a healthy future for us all.
About Dr. Krishna Singhal
Dr. Krishna Singhal received his MS and Ph.D. degrees in Electrical Engineering with focus on MRI safety from Purdue University, under Prof John Nyenhuis in 2018. At Purdue, his research was focused on analysis of metallic shielding for reduction of RF-induced heating of electrodes during MRI for active implants. After graduating from Purdue University, Dr. Singhal worked at Abbott Neuromodulation division in evaluating MRI safety for neuro leads and MRI lab setup. He has active interests in design of MRI safe medical devices, MRI compatibility characterization and electromagnetics.
