Prediction of Force and Image Artifacts Under MRI for Metals Used in Medical Devices

Selection of compatible materials for magnetic resonance imaging (MRI) is a challenging task as severe restrictions are imposed on materials used in and around the scanner due to the static and dynamic magnetic fields involved. Much of the data available for MRI-compatible materials are scattered throughout the literature and are often too device specific. This paper focuses on engineering materials with sufficient strength and stiffness, and with low enough susceptibility to be used in this environment. Experimental results of generic test specimens are used to give comparable performance indicators for candidate materials. As expected, the force varies linearly with susceptibility with good correlation with the theoretical predictions except for brass 360. It is believed the susceptibility for brass 360 in the literature was mistakenly recorded, and our results suggest a value of 112 ppm. The image artifacts were compared based on the radius of the affected area in the image. The theory greatly overpredicts the affected area; however, the trends in terms of susceptibility seem fairly accurate. The size of the artifact increases with susceptibility, echo time, and the use of turbo spin echo over gradient echo sequences. However, the experimental data contradicted the theory by showing no appreciable effect due to bandwidth.