What is the required FFD for an AP/PA coccyx projection?

For an anteroposterior (AP) or posteroanterior (PA) projection of the coccyx, the recommended focal-film distance (FFD) is typically between 38 and 39 inches. This distance helps ensure that the resultant radiograph has the appropriate detail and contrast needed to visualize the small structures of the coccyx clearly.

Using the correct FFD is crucial because it affects the geometric properties of the image, such as magnification and sharpness. In radiography, too short or too long of an FFD can lead to distortions or blurring, thus compromising the diagnostic quality of the image.

Understanding the optimal FFD for different projections aids radiologic technologists in producing high-quality images that accurately represent the anatomical structures being examined, which is fundamental for proper diagnosis and treatment planning.