Cleveland Family Study

16.1 Overview and Background

A cephalometric radiograph is an x-ray of the neck and cranium. Two films are taken in the process, one frontal (P/A) and one profile (Lateral). The participant is positioned in a cephalometer, which is a device for immobilizing the participant’s head so that it does not change position from one exposure to the other. This is accomplished by securing two ear rods in the participant’s ear canals, and a Plexiglas nose brace is placed at the bridge of the participant’s nose.

The purpose for taking the x-ray is to better understand the relationship between craniofacial morphology and its relationship to OSAS. Also, craniofacial morphology over time and the genetically inherited risk factors involved. A cephalometric examination is also an excellent tool for investigating soft tissue risk factors for OSAS, such as tongue size and airway space. Barium Sulfate is administered to the participant just before exposing the lateral film. This contrast medium is used to bring out details of soft tissue not readily seen in the radiograph.

Traditionally, cephs are taken with the participant positioned in Frankfurt Horizontal. Frankfurt Horizontal positions the skull with two landmarks; the Porion (ear hole) and Orbitale (notch on the bottom of the eye socket) parallel to the floor. This is a standard practice so radiographs, taken years apart, could be compared with the skull is in the same orientation. This is the protocol for the present study.

In addition to the participant’s name and date of birth, also recorded on the participant’s chart are ML Distance and P+ Distance. These are records of the distance of the participant’s skull and the x-ray film. Placing a film cartridge next to the participant’s skull and passing x-rays through the skull and onto the film creates a cephalometric x-ray. The image of the skull remains on the film. However, radiation leaving the x-ray tube approaches the target (skull) in a cone shaped beam, getting wider as it travels farther from the original source. As a result, the farther the film cartridge is from the skull, the larger the final image will be as a result of this magnification. To accurately analyze the image, the researcher needs to know the amount of magnification that occurred, so it can be compensated for. The above two distance measures communicate this information to the analyst.