This increases the latitude of the image, allowing the pulmonary tissue to be better visualized. The thoracic cavity inherently has high contrast due to the bony vertebrae, ribs and sternum, the soft tissues of the heart, and aerated lung. Making radiographs with high latitude maximizes our ability to see lung tissue, which is the most difficult task when viewing the thorax. The photoelectric effect and the density of bone allow x-rays to be highly attenuated. Exquisite detail of bone can be achieved.
Abdominal radiography is in the middle of the two above examples.
Higher mAs must be used as well, as there is increased x-ray beam attenuation because of the amount of abdominal organs present. The density of the medium explains the difference in attenuation between two tissues, for example the lungs and the heart. Lungs have a much lower density than solid organs as heart or liver. Therefore, the heart attenuates more x-rays and the resultant radiographic image is more opaque than the lucent lung. The difference in atomic number can explain the contrast produced by contrast media such as barium and iodine.