Radiofrequency induced heating around aneurysm clips using a generic birdcage head coil at 7 Tesla under consideration of the minimum distance to decouple multiple aneurysm clips

Purpose To evaluate radiofrequency (RF) induced tissue heating around aneurysm clips during a 7T head MR examination and to determine the decoupling distance between multiple implanted clips. Methods A total of 120 RF exposure scenarios of clinical relevance were studied using specific absorption rate and temperature simulations. Variations between scenarios included 2 clips (18.8 and 51.5 mm length), 2 MR‐operating modes, 2 head models, and 3 thermoregulation models. Furthermore, a conservative approach was developed to allow for safe scans of patients with aneurysm clips even if detailed information on the implanted clip is unknown. A dedicated simulation‐based approach was applied to determine the decoupling distance between multiple implanted clips. Results For all 60 clinical scenarios with the 18.8‐mm‐long clip, the absolute tissue temperature remained below regulatory limits. For 15 of 60 scenarios with the 51.5‐mm‐long clip, limits were slightly exceeded (less than 1°C). The conservative approach led to a maximum time‐averaged input power of the RF coil of 3.3W. The corresponding B1+ is 1.32 µT. A decoupling distance of 35 mm allows the aneurysm clips to be treated as uncoupled from one other. Conclusion Safe scanning conditions with respect to RF‐induced heating can be applied for single or decoupled aneurysm clips in a 7T ultra‐high field MRI setting. Multiple aneurysm clips separated by less than 35 mm need further investigations.