FIGURE 3. ¹⁸F-FDG (left), WBC (middle), and marrow (right) images. (A) On ¹⁸F-FDG image, there is BPI activity along lateral aspect of femoral component of infected 20-y-old cemented left total hip replacement. Both femoral and acetabular components were loose. Target-to-background ratio was 15.8, consistent with infection. Note extension of activity to lateral surface of thigh, corresponding to sinus tract. Spatially incongruent activity, also extending to thigh surface and consistent with infection, is present on WBC/marrow study. (B) On ¹⁸F-FDG image, BPI activity is present along lateral aspect of femoral component of 5-y-old cementless left total hip replacement with aseptic loosening of both femoral and acetabular components. Pattern is similar to that illustrated in A, but target-to-background ratio in this case was 3.0. WBC/marrow study is negative for infection. (C) Although there is linear area of soft-tissue activity in lateral thigh, there is no BPI activity on ¹⁸F-FDG image of infected 1-mo old hybrid left total hip replacement. Femoral and acetabular components of prosthesis were fixed. WBC/marrow study is consistent with infection.