MRI – Magnetic Resonance Imaging and Simulation
Magnetic Resonance Imaging (MRI) is one of the most widely used and safest imaging modalities for medical diagnostics. Despite this, one of the major technological challenges facing the biomedical imaging world has been the issues created when a patient with metallic medical implants suffers the need (for any reason) for an MRI. With more and more medical implants being used to treat patients, MRI Safety is a growing concern. Consider just a few numbers:
- ~600,000 heart stents (1)
- ~900,000 coronary stents & ~700,000 peripheral artery stents (2, 3)
- 2M stents per annum (4)
- 50.6 MRI exams are performed per 1,000 population – 34 country average and 104.8 MRI exams per 1,000 population – United States (5)
Personally, we know people (and you may too) who are impacted by this current technological limitation. While most implanted devices are accepted as safe for exposure to MRI fields, conditions may arise when there is ambiguity or no specific guidance can be provided, and there is confusion regarding which patients with cardiovascular devices can safely undergo MR examination. Current guidelines based on the results of idealized tests place limits on MR exposure for a large percentage of stents, and the current approach fails to address conditions where finite length stents are joined to form a longer device, and in some cases unsafe examination of patients with implanted devices has occurred (6-10).
MR imaging exposes patients with metallic implants to possible risks associated with interaction with the magnetic field to produce translation or rotation, heating due to interaction with the Radio Frequency (RF) energy, or the development of artifacts on the MR image. Electrically conductive implants such as stents, wires, shunts or leads can act to concentrate the electric field in the vicinity of the device leading to excessive local heating that may cause tissue necrosis. The extent to which the electric field is concentrated is dependent on many parameters related to device design, MR machine characteristics and device location within the body. Hence simply listing a device as either safe or unsafe for MR exposure can fail to accurately represent the conditions under which a patient may be safely examined.
Currently a device’s compatibility with MR exposure is defined through a series of standardized tests that provide only limited representations of patient conditions; these tests are both time consuming and expensive and often fail to consider alternative device arrangements. Integration into patient guidelines is implemented using the “specific absorption ratio” (SAR) rather than temperature, the underlying cause of tissue necrosis. In addition, this approach does not take into account other factors such as the transient nature of the heating and cooling effects due to blood flow over the device or in the surrounding tissue. Thus more sophisticated approaches are required to accurately represent real world scenarios and better define conditions under which patients with implanted devices can be safely exposed to MR imaging.
And more sophisticated approaches are precisely what we are working on. AltaSim is fortunate to be working with people whose aim is to help bring real answers full of factual information by utilizing computational modeling and multiphysics simulation to serve not only the biomedical industry, but also the treating physician and the patient. These efforts align with our motto, “Tomorrow’s Technology Today” and we are excited about the real life possibilities for all involved. Your comments and questions are always welcome.
1. Reuters 2011 from Chan, Journal of the American Medical Association, July 5, 2011
2. MPMN, Volume 27, No. 7, 2011
3. U.S. Markets for Peripheral Vascular Stents, MedTech Insight Report #A254, 2011
4. OECD Health Statistics 2014 – Frequently Requested Data
5. Medtronic web page
6. FDA Public Health Notification: MRI-Caused Injuries in Patients with Implanted Neurological Stimulators, May 2005
7. MRI-Related Death of Patient With Aneurysm Clip, November 1992
8. U.S. Food and Drug Administration, Center for Devices and Radiological Health (CDRH), Medical Device Report (MDR)
9. U.S. Food and Drug Administration, Center for Devices and Radiological Health (CDRH), Manufacturer and User Facility Device Experience Database, MAUDE
10. Cardiovascular Catheters and Accessories, MRISafety.com