Score Evaluation of MRI Sequence Type Related Artifacts after Interbody Fusion with Metallic Implants—A Spine Specimen Study

Introduction: According to anterior spine fusion intervertebral disc spacers made of titanium or cobalt-chromium al-loys are of special interest. With regard to postoperative problems implant related artifacts can lead to a decreased MRI evaluation. The focus of this study was to compare the respective implant artifact artifact range dependend on different MRI sequences. To simplify artifact evaluation we introduced in this study a new developed 0-1-2 score. Material and Methods: We performed an MRI artifact evaluation of 2 different metallic intervertebral disc spacers (cobalt-chromium and titanium alloy). A carcass porcine spine was employed. Considering 12 defined spinal regions of interest we evaluated the respective implant artifact properties independent from the total artifact volume by using a new developed 0-1-2 score. The artifact range was documented for 15 different MRI-sequences. Results: For the titanium spacer as well as the cobalt-chromium-spacer an MRI evaluation of the implant/disc space situation could not be carried out. In contrast to the cobalt chromium spacer the titanium spacer allowed a good differentiation of the spinal canal opposite to the implant. Optimal MRI imaging results for both metallic intervertebral disc spacers could be achieved considering TSE sequences. Conclusion: A comparison of these two metallic spacers showed in all examined sequences clear advantages in favour of the titanium spacer. The best MRI representation of both tested implants by reducing implant related artifacts could be achieved with fast spin echo (TSE-) sequences. In spite of the use of TSE sequences a variability of susceptibility artifacts has to be included with regard to implant shape and material. With regard to the results of this study the easy use of a new developed artifact score represented a useful help to compare implant related MRI artifact properties independent from the actual implant related total artifact volume.

Bulk Metallic Glasses: MRI Compatibility and Its Correlation with Magnetic Susceptibility

Several bulk metallic glasses （BMGs） were selected to in vitro assess their magnetic resonance imaging （MRI） compatibility with agarose gel as a phantom, in terms of the extent of susceptibility artifacts in magnetic resonance image. The investigated metals include the Au49Ags.sPd2.3Cu26.9Si16.3, Zr61Ti2Cu2sA112, Cu50.4Nis.0Ti31Zr13 and Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2, together with pure titanium （CP-Ti） and Co-28Cr-6Mo alloy （ASTM-F799） for comparison. The artifact extent in MR images was quantitatively characterized according to the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo （FSE） sequence and gradient echo （GRE） sequence. As indicated, artifact severity of the BMGs is much less than that of the CoCrMo alloy. The AuAgPdCuSi BMG manifested the smallest arti- fact among the four BMGs, while the TiCuZrFeSnSiAg BMG is comparative to the CP-Ti. The MRI compatibility of BMGs is ranked as a sequence of the Au-, Zr-, Cu- and Ti-based alloys. Dependence of material mag- netic susceptibility on artifact extent is also the case of the BMGs, even though it does not follow a simple linear relationship within a range of △χv = 30-180 ppm. These findings are of interest to reveal that the BMGs are potentially applied in the fields associated with an interventional MRI for MRI-guided surgeries.