What is the recommended source-to-image distance for an AP projection of the tibia and fibula?

What is the recommended source-to-image distance for an AP projection of the tibia and fibula?

• A. 60 inches (152 cm)
• B. 72 inches (183 cm)
• C. 20 inches (50 cm)
• D. 40 inches (102 cm)

Answer: (D)

Understanding source-to-image distance helps manage magnification and sharpness. For an AP projection of the tibia and fibula, the goal is to include the entire bone with both joints on one image while keeping the image size close to true anatomy. A distance of forty inches (about 102 cm) achieves that balance. It’s long enough to minimize magnification so the tibia’s length is depicted accurately, yet short enough to fit the knee and ankle joints within the field and keep the setup practical. Short distances would magnify the image and distort size, while very long distances aren’t needed for this exam and can complicate positioning and field coverage.

Understanding source-to-image distance helps manage magnification and sharpness. For an AP projection of the tibia and fibula, the goal is to include the entire bone with both joints on one image while keeping the image size close to true anatomy. A distance of forty inches (about 102 cm) achieves that balance. It’s long enough to minimize magnification so the tibia’s length is depicted accurately, yet short enough to fit the knee and ankle joints within the field and keep the setup practical. Short distances would magnify the image and distort size, while very long distances aren’t needed for this exam and can complicate positioning and field coverage.