How should the measure be taken for a lateral coccyx x-ray?

For a lateral coccyx x-ray, the measurement should be taken at the level of the central ray. This is crucial because the central ray defines where the x-ray beam is directed and ensures that the area of interest—the coccyx—is accurately visualized.

Taking the measure at the level of the central ray helps to position the patient correctly for optimal imaging. It ensures that the x-ray beam will properly penetrate the desired anatomical area, providing clear, diagnostic images while minimizing unnecessary radiation exposure to surrounding tissues. This practice reinforces the principles of precision and safety in radiographic techniques.

The other options do not align with the standard protocol for obtaining a lateral coccyx x-ray, as the waist, coccyx itself, or the sacrum may not accurately represent the area being targeted for imaging. Therefore, the focus on the central ray emphasizes the importance of correct positioning in radiographic procedures.