Investigation of the heating effect of MRI on the patients with metallic orthopaedic implant materials

Abstract

It is increasingly becoming common that orthopaedic patients are having implant materials in their body. On the other hand MRI with its potential diagnostic value can not be utilised well on the patients with metal implants due to potential hazardous interaction of metal and magnetic field. Normally, if a metal is facing a magnetic field change, there is the induction of eddy currents on the metal and the induced currents are being dissipated through the resistance of the metal, producing heat. The aim of this study is to investigate the temperature rise due to metal implant and MRI interaction. For this purpose we have prepared a phantom, which comprises a metallic implant embedded in polyacrylamide gel in order to simulate the human tissue and the implant material inside. This phantom is scanned under MRI using the common protocols for the orthopaedic patients. The temperature rise has been monitored during the scanning. A theoretical model of the heat dissipation has been established. Eddy current induction on metals is due to the change of magnetic field applied on the metal planes. There are two sources of magnetic field in MRI, the gradient field and the RF field. It has been observed that there is a temperature rise due to the gradient fields and the RF system of the MRI equipment. As a result of this study we showed that using present MR technology the amount of the temperature rise observed remains within the tolerable range not to cause tissue necrosis when the implant is made of stainless steel metal.