RESUMEN
OBJECTIVE: To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images.MATERIALS AND METHODS: Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders.RESULTS: k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging −1.07 to −0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation.CONCLUSION: Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.
RESUMEN
Femoral neck fractures are associated with femoral shaft fractures in 1% to 9% of cases. Undisplaced neck fractures are susceptible to displacement during shaft nailing. We report the case of a 57-year-old male patient in whom we performed standard intramedullary nailing for a femoral shaft fracture. In doing so, we identified a vertical radiolucent line at the femoral neck, which was thought to be further displacement of a hidden silent fracture or an iatrogenic fracture that developed during nail insertion. Consequently, we decided to switch to reconstructive femoral nailing. Postoperative hip imaging failed to show the femoral neck fracture that we saw in the operating room. Here, we discuss the aforementioned case and review the literature concerning this artifact.