MR Imaging in the Presence of Small Circular Metallic Implants

Purpose: the thermal effects of MR imaging in the presence of circular nonferromagnetic metallic implants were studied in 6 rabbits.Material and Methods: A sternotomy was performed and fixed with stainless steel wires, and small titanium rings (diameter 3 mm) were placed on the surface of the ascending aorta and subcutaneous tissue of the thigh. Four of the rabbits were exposed to an imaging procedure with a 1.5 T scanner applying a T1-weighted spin-echo sequence and a gradient echo sequence. Two of the animals served as unexposed controls. Thirty- six hours after the exposure, tissues adjacent to the implants were examined histologically and compared with corresponding samples of the control animals.Results: In the area of the titanium rings, histologic analysis revealed slight inflammatory changes apparently caused by the operation. No evidence of thermal injury was found, suggesting that the presence of the rings does not contraindicate MR examinations. Necrosis was noted in all of the sternal specimen...