Magnetic-susceptibility of Au-Pt-Nb Alloy for Magnetic-resonance-imaging Compatible Biomedical-devices

Objectives: Metal-artifact due to magnetic-susceptibility (χ) mismatch between alloy and human-tissue is one of the serious magnetic-resonance-imaging (MRI) artifacts. Alloys of subzero susceptibility (to be precise, close to the volume susceptibility (χ_v) of human-tissue, approximately -9ppm) are thus required for MRI-artifact-free metal-biomedical-devices. Au-28%Pt alloy is a candidate because of its χ_v and high corrosion resistance. The mechanical-properties are, however, insufficient for various types of biomedical-device. Addition of a third element is a popular method to improve the mechanical-properties of a binary-alloy, but the effect on χ_v is unknown. In this study, the effects of Nb addition to Au-Pt alloy on the χ_v and mechanical-property were investigated.

Methods: Several Au-Pt-Nb alloy ingots from 5 to 40%Pt and 4 to 12%Nb were fabricated by argon-arc-melting. The ingots were then hot-rolled at 973K under vacuum. The Vickers hardness (Hv) of the ingots as fabricated and after aging at 823 and 973K were measured. χ_v of the hot-rolled specimens was measured using a magnetic-susceptibility-balance.

Results: The χ_v of Au-5Pt-4Nb, Au-5Pt-8Nb and Au-5Pt-12Nb alloys were -24, -9 and 2ppm (SD<2%), respectively, indicating that χ_v increased with increasing Nb content (p<0.01, t-test). On the other hand, the χ_v of Au-10Pt-8Nb, Au-15Pt-10Nb, Au-20Pt-11Nb, Au-25Pt-8Nb, Au-30Pt-8Nb, Au-35Pt-8Nb and Au-40Pt-8Nb alloys were -10, -9, -1, -13, -10, -10 and -6ppm (SD<2%), respectively, indicating that χ_v was insensitive to Pt content. The maximum Hv of the above MRI-artifact-free alloys as fabricated was 214±5 (Au-20Pt-11Nb alloy), and that after aging was 221±10 (Au-5Pt-8Nb alloy, 973K). Both Hv were significantly higher (p<0.01, t-test) than the maximum Hv of Au-28%Pt alloy, 143±17 (823K aging).

Conclusion: Au-Pt-Nb alloy containing less than 40%Pt and approximately 8%Nb is a candidate MRI-artifact-free alloy. Nb addition to Au-Pt alloy can improve the mechanical-properties and expand the application of the alloy to various types of biomedical-device.