As previously stated, proper positioning is required to obtain the most information from a radiographic image. However, to acquire that image, both the remains and the image receptor must maintain the precise position during the duration of the x-ray exposure. Cardboard and other solid materials are radiopaque, impeding the passage of x-rays and causing the material to be visible on the processed radiograph. The positioning aid must be radiolucent, or "nearly invisible," to x-rays. There are commercially available foam shapes such as wedges and blocks that are used routinely in imaging facilities (Figure 2.39), but they are expensive and bulky to transport. Generally, foam pads can be purchased in any large city or town near to where the study will be completed. Foam pads of various thicknesses can be purchased and then cut into required shapes (Figure 2.40).
Figure 2.35A Positioning for a PA Caldwell projection of the skull. The canthomeatal line (A) should be perpendicular to the film plane (B). In order to achieve the correct angle, a commercially available positioning aid (C) was placed between the skull and the cassette. The center ray of the x-ray beam (D) was directed to form a 15° caudal angle to the canthomeatal line (A) and exited through the glabella (E).
For skeletal remains, positioning aids are also necessary. Since only minor adjustments may be required and individual bones are not very heavy, small pieces of foam padding will achieve the desired results (Figures 2.41A and 2.41B).