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Figure 2b. Comparison of metal-related artifacts according to the physical composition and size of the metallic object and the MR pulse sequence used. (a) Schema shows the relative positions of a titanium-alloy screw (diameter, 4.5 mm) and two stainless steel screws (diameters, 3.5 and 4.5 mm) within the phantom. (b, c) Axial MR images of the phantom, obtained with a gradient-recalled echo (GRE) sequence (repetition time msec/echo time msec, 500/14; flip angle, 80°) (b) and a fast spin-echo (SE) sequence (500/14; echo train length, 16) (c), show that the titanium alloy screws produced smaller artifacts than did the stainless steel screws, regardless of the sequence used. The artifacts are smaller on c than on b. The arrow in b shows the direction of the frequency encoding gradient.
