Direct Temperature Measurements of Cardiac Stent during MRI Examinations

Nowadays, Magnetic Resonance Imaging (MRI) is considered the gold standard for imagingthe brain, spinal cord, musculoskeletal system, head and neck, and complex congenital heartmalformations; consequentially, the number of MRI scans in patients with implantable electronicdevices has simultaneously increased. During the entire length of the MRI exam, patients are exposedto electromagnetic fields with different characteristics (static, low frequency, radiofrequency fields),which are related to different risks. The scarce available literature about MRI-induced heating oncardiac stents suggests that excessive temperature rise occurs only in unfavorable cases. Ideally, RFsafety assessment could be performed during the anamnestic process, but this simulation process'sresults are too slow to be performed before patient MRI examination. In this context, we developeda dedicated measurement set-up by focusing our target on the measurement of the heating of acardiac stent during an MRI examination. Results for the temperature rise trend along the entirestent length during a clinical MRI protocol are shown together with the local Specific AbsorptionRate (SAR) values and cumulative equivalent minutes at 43 C (CEM43C), in order to ensure thesafety of patients with MR-conditional devices, also with a view to not inappropriately precludetheir access to MRI scans. The obtained results show that the maximum temperature rise (4.12 C) iswithin the limit of 5 C stated in the stent manual for 15 min of continued scanning with the specificconditions. The maximum temperature rise was in correspondence with the stent tips and calculatedSAR confirms the fact that two hotspots are present near the tips of the stent. Finally, the calculatedCEM43C remained well below the proposed threshold for muscle tissue.