UCSF Radiology
SAFETY IN MRI IN PATIENTS WITH CORONARY STENTSBACKGROUNDTo our knowledge, the FDA has not approved any MRI unsafe coronary stents; existing devices are considered either MR safe or MR conditional depending upon the metallic alloy from which they have been constructed. Because they are not subject to magnetic deflection or heating, all non-metallic stents are considered MR safe. As such, patients with these devices may be imaged safely at 1.5T or at 3T at any time, including immediately, after stent placement.In contradistinction to MR safe, non-metallic stents, there are a number of weakly ferromagnetic stents that are commonly used in patients with coronary artery disease (including some drug-eluting stents). Because they are subject to the theoretical risk of stent heating or magnetic deflection, these devices are considered MR conditional. Heating of <2 degrees Celsius has been documented in some of these devices in laboratory experiments with high RF power deposition, as have mild mechanical torque on the devices due to interactions with the main magnetic field. Although rigorous safety data is not available for all devices, due to normal blood flow and the inherent anchoring of these devices that occurs during placement, these risks are considered negligible. The risk of device displacement falls further after a period of 6-8 weeks, during which tissue ingrowth around the stent results in further resistance to mechanical displacement. Of note, there have been no adverse MRI events related to imaging in patients with coronary stents reported in the literature.POLICYIn accordance with available data, the UCSF Department of Radiology & Biomedical Imaging has adopted the following policy for MRI in patients with coronary stents:1. The presence of coronary stents, including the date of placement and the device manufacturer, should be ascertained and documented in all patients prior to undergoing MRI.2. Patients with non-metallic (MR safe) coronary stents may be imaged at 1.5T or 3T at any time following device placement.3. Patients with weakly ferromagnetic (MR conditional) coronary stents should be imaged at 1.5T until a period of 6 weeks has elapsed after device placement. If more than 6 weeks has elapsed, 3T imaging is acceptable with following constraints:Maximum spatial gradient magnetic field of 720-Gauss/cm or less (a higher value for the spatial gradient magnetic field may apply if properly calculated).Maximum MR System reported whole-body-averaged specific absorption rate (SAR) of 2-W/kg for 15 minutes of scanning (per pulse sequence).4. Patients for whom device information is not available should be imaged as per #3 above under the assumption that they have MR conditional stents implanted.BM/MH/CH 12/18/2015 ................
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