[MUSIC PLAYING] Hey, everybody. Welcome back. This lesson is about a type of radiographic distortion called shape distortion. Shape distortion is when the anatomy of interest looks shorter or longer on the radiograph than the anatomy truly is. The image of the anatomy will not be true to the actual shape of the object if the X-ray tube, image receptor, or anatomy of interest are out of alignment. Shape distortion is important to be aware of as it can affect a radiologist's ability to accurately diagnose a pathology. Shape distortion can cause misrepresentation of the size or position of a patient's anatomy or pathology. There are two types of shape distortion, foreshortening and elongation. Foreshortening is when the anatomy of interest appears shorter on the radiograph than the anatomy truly is. Elongation is when the anatomy of interest appears longer on the radiograph than the anatomy truly is. Foreshortening occurs when the anatomy of interest is not parallel to the image receptor. If the anatomy is angled towards or away from the image receptor, the shadow of the anatomy is now superimposed on itself, causing foreshortening. As the anatomy angulation increases, foreshortening increases. Foreshortening can be avoided through patient positioning. For example, we invert the toes during hip imaging, which causes rotation of the femur and brings the femoral neck parallel to the image receptor. By positioning the patient in this way, we avoid foreshortening of the femoral neck. Elongation is present when the radiographic image appears longer than the actual anatomy being examined. Elongation occurs as a result of X-ray tube or image receptor angulation. The X-ray tube may be perpendicular to the anatomy but not perpendicular to the image receptor. The image receptor may be parallel to the anatomy. But the X-ray tube may be angled. As the X-ray tube or image receptor angulation increases, elongation increases. Basically, any time that the central beam is out of alignment, it increases the angle of the beam and causes the image of the object to appear stretched out or elongated on the radiograph. Shape distortion is sometimes used to better visualize the anatomy of interest. For example, radiographs taken of the sternum at an oblique angle will distort some of the anatomy but will show joint space better and prevent superimposition of the spine. Another example is the town's view of the skull where the X-ray tube is intentionally angled 30 degrees, and that can help with identifying skull fractures. In situations where patients cannot be positioned parallel to the image receptor, the law of isometry can be used to minimize foreshortening. The law of isometry states that the central ray should be set at half of the angle formed between the object and the image receptor to minimize foreshortening. For example, if an injury causes a patient's femur to be at a 30-degree angle to the image receptor, the central ray should be angled at half of that, which is 15 degrees. This angling of the central ray will help to prevent the appearance of foreshortening. In summary, shape distortion is a result of angulation either of the anatomy of interest, the X-ray tube, or the image receptor. Angulation of any of these factors affects the position of the target anatomy within the X-ray beam and affects its appearance on the radiograph. Foreshortening, which is when the radiographic image appears shorter than the actual anatomy being imaged, only occurs when the anatomy is not parallel to the image receptor. Elongation-- that's when the radiographic image appears longer than the actual anatomy being examined-- can be caused by X-ray tube or image receptor angulation.