Shape distortion is caused by

Shape distortion is caused by

• A. Film fog due to scatter
• B. Misalignment of tube-part-film relationship
• C. Short exposure time
• D. Increase in mA

Answer: (B)

Shape distortion comes from incorrect projection geometry: if the x-ray beam, the body part, and the image receptor aren’t aligned, the part’s image on the film will be stretched or compressed. The central ray should be perpendicular to the image receptor and the part should lie parallel to the receptor so the image is true to size. When the tube, part, and film aren’t in a straight line, you get elongation or foreshortening, which is distortion. This is why misalignment of the tube-part-film relationship is the best answer. Film fog from scatter mainly affects contrast, not shape. A short exposure time reduces motion blur, not distortion. Increasing mA changes density, not geometry.

Shape distortion comes from incorrect projection geometry: if the x-ray beam, the body part, and the image receptor aren’t aligned, the part’s image on the film will be stretched or compressed. The central ray should be perpendicular to the image receptor and the part should lie parallel to the receptor so the image is true to size. When the tube, part, and film aren’t in a straight line, you get elongation or foreshortening, which is distortion.

This is why misalignment of the tube-part-film relationship is the best answer. Film fog from scatter mainly affects contrast, not shape. A short exposure time reduces motion blur, not distortion. Increasing mA changes density, not geometry.