Effect of Manganese Content on the Magnetic Susceptibility of Ferrous-Manganese Alloys: Correlation between Microstructure on X-Ray Diffraction and Size of the Low-Intensity Area on MRI

ABSTRACT

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 alpha'-martensite, gamma-austenite, and epsilon-martensite were seen on XRD, and their composition changed from alpha'-martensite to gamma-austenite and/or epsilon-martensite, with increasing Mn content. The Fe-10Mn and Fe-15Mn specimens comprised alpha'-martensite, the Fe-20Mn and Fe-25Mn specimens comprised gamma+epsilon phases, and the Fe-30Mn and Fe-35Mn specimens exhibited a single gamma 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 gamma-austenite and/or epsilon-martensite.