What is the FFD (Source-to-Image Distance) for a lumbar oblique X-ray?

The source-to-image distance (FFD), also known as the focus-to-film distance, is a crucial parameter in radiographic imaging that affects both the geometry and quality of the X-ray image. For a lumbar oblique X-ray, the recommended FFD is typically 40 inches.

Using a 40-inch distance is standard because it strikes a balance between achieving proper magnification and maintaining adequate detail in the images. This distance reduces geometric distortion and enhances image sharpness, which is vital for accurately assessing the lumbar spine's anatomy.

Other distances such as 36 inches, 44 inches, and 50 inches may not provide optimal conditions for the imaging of the lumbar spine and could introduce various issues, including increased magnification, loss of detail, or inadequate exposure levels. Therefore, 40 inches is the appropriate choice for lumbar oblique X-rays to ensure high-quality diagnostic images.