Artifact Examination of Oxidized Nitinol Wire in MRI at 0.3; 1.0 and 1.5 T

Daniel Sachtler, Dep. of Physical Engineering, University of Applied Sciences, Gelsenkirchen, Germany

Alan Pelton, Christine Trepanier, J&J ND&C, Fremont, CA, USA

Andreas Melzer, INSITE med. & Dept of Physical engineering University of Applied Sciences, Gelsenkirchen, Germany

Background

MRI examination of susceptibility artifacts related to the oxide of Ti49.8Ni50.2 medical grade wire.

Material & Methods

3mm diameter Nitinol wire was annealed at 1000°C for 30 minutes, centerless grounded and electro-polished. 30mm sections (d=1mm) were oxidized in air at 400-1.000°C for 10 minutes. Oxide thickness was measured by FIB/SEM. Microscopic photos were taken. The response on a magnet was tested. Sections were examined in a 0.3T Hitachi and in 1.0/1.5T Philips. Samples were placed in a water filled test container, parallel and perpendicular to the main field. A Plexiglas bar with drill holes was used to fix samples. Spin (TR/TE=300/30ms) and gradient (TR/TE=100/6ms, FA=40°) echo images were obtained using the head coil.

Results

Oxide layers of 0.0338µm at 400°C up to 21.9µm at 1000°C were produced. Initial oxide thickness was 11nm. Thicker oxide layers are brittle and tend to flake. Up to 700°C samples showed no magnetic attraction, 1000°C strongest attraction. Parallel orientation does not cause artifacts in contrast to perpendicular. No artifact differentiation for up to 700°C, 1000°C strongest artifacts. From 0.3T to 1.5T the artifact size changes from 25x to 47x the original size for 1000°C.

Conclusion

Increased oxide thickness causes stronger artifacts and samples become magnetisable. Samples up to 700°C need to be better investigated for further comparison. Investigations should also be done at 3.0T.

Keywords

Nitinol, Nitinol oxide