D. D. Gorhe, Zimmer Inc., Warsaw, IN; J. Nyenhuis, Purdue University, West Lafayette, IN; J. P. Anderson, Zimmer, Inc., Warsaw, IN
Magnetic Resonance Imaging (MRI) is a commonly accepted and widely used medical procedure. Implants made from ferromagnetic materials will experience force and torque due to the large static magnetic field that is present in MRI. Most hip and knee implants are manufactured from non-ferromagnetic cobalt and titanium based alloys, which will minimize force and torque. Irrespective of the magnetic characteristics of the implant alloys, the Radio Frequency (RF) magnetic field present in the MRI environment may, under certain circumstances, result in heating of the devices and the surrounding tissue. Metallic implants can also produce image artifacts that can compromise the image quality. In this work, commonly used hip and knee implants were tested using a standardized rectangular phantom model in 1.5T MRI systems for RF induced heating, force, and image artifacts. The RF induced heating was below the level required to pose hazard to the patient and there was negligible force, as measured using a standard deflection test. As expected, the heating was greatest at the ends of the implants. Image artifacts were minimal owing to the essentially non-ferromagnetic nature of the materials used in these devices. The RF induced heating was also investigated using a phantom whose shape more closely matches that of the human body. In-vitro temperature rises measured with this more anatomical phantom are expected to result in better prediction of the in-vivo temperature rise during MRI.
Summary: Magnetic Resonance Imaging is a commanly accepted and widely used medical procedure. In this study, commonly used knee and hip implants were tested using a standardized rectangular phantom in 1.5T and 3.0 T MRI systems for RF induced heating, force, and image artifacts.
