Quantitative assessment of an MR technique for reducing metal artifact: application to spin-echo imaging in a phantom

Objective. To quantify image artifact reduction using a new technique (MARS - metal artifact reduction sequence) in vitro. Design. Coronal T1-weighted MR images were obtained through two metal phant oms (titanium/chromium-cobalt and stainless steel femoral prostheses) immer sed in water. Comparison of artifact volume was made with images obtained u sing conventional and modified (MARS) T1-weighted sequences. Signal intensi ty values outside a range of +/- 40% the average signal intensity for water were considered artifact and segmented into low or high signal artifact ca tegories. Considering the arbitrary selection of this threshold value, volu metric calculations of artifact were also evaluated at +50%, 60%, 70%, and 80% the mean signal for water. Results. Conventional T1-weighted images produced 87% more low signal artif act and 212% more high signal artifact compared with the MARS modified T1-w eighted images of the stainless steel prosthesis. Conventional T1-weighted images of the titanium prosthesis produced 84% more low signal artifact and 211% more high signal artifact than the MARS modified sequence. The level of artifact reduction was essentially uniform for the various threshold lev els tested and was greatest at +/- 20% the global signal intensity average for water. Conclusion. The MARS technique reduces the volume of image signal artifact produced by stainless steel and titanium/chromium-cobalt femoral prostheses on T1-weighted spin-echo images in a tissue phantom model.