Artefacts and ferromagnetism dependent on different metal alloys in magnetic resonance imaging. An experimental study

The authors evaluated the significance of different metal alloys used in or thopaedic surgery in producing artefacts during magnetic resonance imaging. Several MRI sequences were tested and magnetic effects evaluated. Twelve discs made of different metal alloys from three manufacturers were e xamined. These discs were placed in a plastic box with a defined position i n ultrasound gel. Then a sensitive, standard T1 weighted gradient echo sequ ence (TE: 4.1 ms; TR 9.4) was carried out in a coronal plane (Matrix 128/25 6). A Phillips Easy Vision workstation was used for image analysis. The lar gest area of artefact formation, including the surface size of the disc, wa s calculated using a special software program. In order to minimise the mea surement error all discs were measured 10 times and the average value was d etermined. Then eight different sequences were run and measured in the same way. In a second series, all discs were placed separately on metric paper and subjected to the magnetic field of the MRI in order to detect possible motion secondary to the magnetic field applied. The different titanium alloys showed average distortion areas of from 245 m m(2) (Ti6Al4V) to 349 mm(2) (Ti5Al2.5Fe). Cobalt chrome alloys yielded diff erences of between 600 mm(2) and 651 mm(2) and iron alloys of between 902 m m(2) (316L or Fe18Cr10NiMo) and 950 mm(2) (Fe22Cr10N14Mn2MoNb) on average f or the standard T1 weighted gradient echo. The artefact areas were dependent on the different sequences performed. For steel, (Fe18Cr10NiMo) areas of from 411 mm(2) (T1TSE) to 2027 mm(2) (EPI/3 D/SPIR) were measured. All sequences studied produced different artefact pi ctures. None of the materials tested showed changes in position secondary t o ferromagnetism. The size of signal distortion by MRI depends on the alloy making up the imp lanted material and the sequences used. The smallest artefacts occurred wit h the turbo-spin-echo sequences (TSE). The alloys tested in our study seem to carry no risk for patients of ferrom agnetically induced secondary loosening caused by MRI scanning.