Next, the reader must determine whether the film is adequately exposed. Underpenetration can increase or even create the appearance of alveolar densities, and overpenetration can burn through similar alveolar densities so that they are not appreciated. One can judge the degree of penetration by evaluating how well the thoracic vertebrae are seen through the heart shadow. In a properly exposed film, one should just be able to make out the thoracic vertebrae and also be able to look through the cardiac shadow to see structures in the left lower lobe of the lung, especially the lower lobe vasculature.
The third evaluation a reader must make is to determine whether the film has been taken in adequate inspiration (Fig. 3.2). Expiratory films can often mislead the reader into thinking there are densities and infiltrates in the lower lobes. An expiratory film may also mislead the reader into misinterpreting the size of the cardiac shadow. If the patient has taken an adequate inspiration, the right hemidiaphragm should be at approximately the 9th or 10th rib when counting the posterior ribs. Sometimes it is difficult to count the upper ribs on the right. Start by finding the anterior portion of the 1st and then the 2nd rib (the anterior ribs can almost always be seen). Trace the 2nd rib back and find the 2nd rib posteriorly. Count down. When the right hemidiaphragm is at the 11th or 12th rib, the patient probably has chronic obstructive pulmonary disease (COPD).
Figure 3.2 These films reveal the significant changes in heart size and pulmonary volume that occur during inspiration and expiration.
Remember, if the film is not technically adequate the reader should request that the technologist return and get an adequate film. This will permit an accurate interpretation, and you will not be misled by poor technique.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
