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Nanostructured Materials Lab

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Effect of Manganese Content on the Magnetic Susceptibility of Ferrous

Purpose: There is an ongoing search for a stent material that produces a reduced
susceptibility artifact. This study evaluated the effect of manganese (Mn) content on
the MRI susceptibility artifact of ferrous-manganese (Fe-Mn) alloys, and investigated
the correlation between MRI findings and measurements of Fe-Mn microstructure on
X-ray diffraction (XRD).
Materials and Methods: Fe-Mn binary alloys were prepared with Mn contents
varying from 10% to 35% by weight (i.e., 10%, 15%, 20%, 25%, 30%, and 35%;
designated as Fe-10Mn, Fe-15Mn, Fe-20Mn, Fe-25Mn, Fe-30Mn, and Fe-35Mn,
respectively), and their microstructure was evaluated using XRD. Three-dimensional
spoiled gradient echo sequences of cylindrical specimens were obtained in parallel
and perpendicular to the static magnetic field (B0). In addition, T1-weighted spin
echo, T2-weighted fast spin echo, and T2*-weighted gradient echo images were
obtained. The size of the low-intensity area on MRI was measured for each of the Fe-
Mn binary alloys prepared.
Results: Three phases of α’-martensite, γ-austenite, and ε-martensite were seen
on XRD, and their composition changed from α’-martensite to γ-austenite and/or ε
-martensite, with increasing Mn content. The Fe-10Mn and Fe-15Mn specimens
comprised α’-martensite, the Fe-20Mn and Fe-25Mn specimens comprised γ+ε
phases, and the Fe-30Mn and Fe-35Mn specimens exhibited a single γ phase. The size
of the low-intensity areas of Fe-Mn on MRI decreased relative to its microstructure
on XRD with increasing Mn content.
Conclusion: Based on these findings, proper conditioning of the Mn content in Fe-
Mn alloys will improve its visibility on MR angiography, and a Mn content of more
than 25% is recommended to reduce the magnetic susceptibility artifacts on MRI.
A reduced artifact of Fe-Mn alloys on MRI is closely related to the paramagnetic
constitution of γ-austenite and/or ε-martensite.