MRI に適合する医療用金合金の開発

Metal-artifact due to volume-magnetic-susceptibility (χ) mismatch between alloy and human-tissue is one of the serious magnetic-resonance-imaging (MRI) artifacts. Alloys of susceptibility close to that of human-tissue (approximately -9 ppm) are thus required for MRI-artifact-free metal-biomedical-devices. Au-28 mass%Pt alloy is a candidate because of its χ and high corrosion resistance. However, the mechanical properties are insufficient for various types of biomedical-device. The authors found that Nb addition could improve the mechanical properties and simultaneously keep the alloy MRI-artifact-free. The authors produced an Au-8Nb-5Pt alloy wire and found that the χ value for this wire increased because of contamination during the production process. To adjust χ, the Nb content in the alloy was optimized and an Au-7Nb-5Pt alloy wire was produced. The χ value of this wire was confirmed to be close to -9 ppm. The Au-7Nb-5Pt alloy wire demonstrates higher mechanical properties than those of Au-28Pt alloy wire, and good formability. Recently, the authors are successfully producing several kinds of experimental vascular devices, such as coils for cerebral aneurysm embolization, cerebral aneurysm clips, and vascular stents. The next step of the current development is to evaluate the mechanical properties of these experimental devices, and to optimize the device designs for clinical usage.