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. Iodinated contrast media, for example, are translucent liquids that look like water. Radiographic contrast is due to the combined effect of difference in tissue density and atomic number.