Abstract:

For patients with implanted cardiac pacemakers, Magnetic Resonance Imaging (MRI) is still contra-indicated. Coupling of RF-fields into metallic leads of pacemakers can induce currents, that warm up the tissue near the electrode. Estima- tions of this heating effect are commonly obtained either by experimental setups or numerical simulations with continous RF-excitation based on average SAR values. As during real MRI RF-fields are applied in pulsed sequences, high radiation powers occur for short timespans, followed by pauses that could act as cooling time. To determine deviations of thermal heating subject to pulsed and continous excitation, a series of numerical simulations with a saline filled phantom inside a birdcage coil was performed. All simulation parameters were set according to a real 1.5 T MRI system with 64 MHz. This study revealed that by modelling pulsed excitation patterns and a corresponding downscaled continous excitation, a good estimation of heating during real MRI sequences can be achieved. Using a fine mesh, peak temperature rise could be localized more precisely and showed to be highly concentrated.