MR-IMAGING IN THE PRESENCE OF SMALL CIRCULAR METALLIC IMPLANTS - ASSESSMENT OF THERMAL-INJURIES

Purpose: The thermal effects of MR imaging in the presence of circular nonferromagnetic metallic implants were studied in 6 rabbits. Materia l and Methods: A sternotomy was performed and fixed with stainless ste el wires, and small titanium rings (diameter 3 mm) were placed on the surface of the ascending aorta and subcutaneous tissue of the thigh. F our of the rabbits were exposed to an imaging procedure with a 1.5 T s canner applying a T1-weighted spin-echo sequence and a gradient echo s equence. Two of the animals served as unexposed controls. Thirty-six h ours after the exposure, tissues adjacent to the implants were examine d histologically and compared with corresponding samples of the contro l animals. Results: In the area of the titanium rings, histologic anal ysis revealed slight inflammatory changes apparently caused by the ope ration. No evidence of thermal injury was found, suggesting that the p resence of the rings does not contraindicate MR examinations. Necrosis was noted in all of the sternal specimens. This was probably postoper ative, but it impaired the assessment of thermal injury in this area.