What is the correct focal film distance (FFD) for a lateral ankle X-ray?

The correct focal film distance (FFD) for a lateral ankle X-ray is 40 inches. This distance is chosen to optimize image quality while minimizing patient exposure to radiation. In radiography, the FFD (also known as Source-to-Image Distance or SID) affects the geometry of the X-ray beam and the amount of scatter radiation that can occur. At 40 inches, the beam is sufficiently collimated to ensure that the anatomy of the ankle, including the bones and joints, is clearly visualized. This distance strikes a balance between producing a high-quality image and maintaining safety protocols for both the patient and the healthcare provider.

Choosing the appropriate FFD is crucial in radiographic practice, as it significantly impacts the overall diagnostic value of the image captured. An FFD that is too short may result in magnification and decreased image sharpness, while one that is too long can increase the dose of radiation received by the patient without providing additional benefits. Thus, 40 inches is the standard for ensuring accurate representation of the lateral ankle anatomy.