When does foreshortening occur in radiography?

Foreshortening occurs when the object being imaged is angled relative to the central ray (CR) and the image receptor (IR) is positioned perpendicular to the CR. This geometric distortion results in a compressed appearance of the object in the final radiographic image, making it appear shorter than its true length.

When an object is not aligned properly with the CR, the projection of the object onto the IR is not accurate, leading to the foreshortened effect. This is particularly evident with elongated or tubular structures, such as bones, where the angling may cause the radiographic length to appear significantly less than the actual length.

In contrast, alignment of the object with the CR or tilting the image receptor does not lead to foreshortening in the same manner. Similarly, an exposure time that is too short primarily affects image quality through motion blur rather than geometric distortion like foreshortening. Understanding the relationship between the position of the object, CR, and IR is crucial for accurate radiographic imaging, and proper alignment is essential to avoid foreshortening.