Posteroanterior Radiograph

The standard PA chest radiograph is obtained by having the patient stand (or sit) in the upright position. The anterior aspect of the patient’s chest is pressed against a film cassette holder, with the shoulders rotated forward to move the scapulae away from the lung fields. The distance between the x-ray tube and the film is 6 feet. The x-ray beam travels from the x-ray tube, through the patient, and to the x-ray film.

The x-ray examination is usually performed with the patient’s lungs in full inspiration to show the lung fields and related structures to their greatest possible extent. At full inspiration the diaphragm is lowered to approximately the level of the ninth to eleventh ribs posteriorly (Figure 7-1). For certain clinical conditions, radiographs are sometimes taken at the end of both inspiration and expiration. For example, in patients with obstructive lung disease an expiratory radiograph may be made to evaluate diaphragmatic excursion and the symmetry or asymmetry of such excursion (Figure 7-2).

Anteroposterior Radiograph

The supine AP radiograph may be taken in patients who are debilitated, immobilized, or too young to tolerate the PA procedure. The AP radiograph is usually taken with a portable x-ray machine at the patient’s bedside. The film is placed behind the patient’s back, with the x-ray machine positioned in front of the patient approximately 48 inches from the film.

Compared with the PA radiograph, the AP radiograph has a number of disadvantages. For example, the heart and superior portion of the mediastinum are significantly magnified in the AP radiograph. This is because the heart is positioned in front of the thorax as the x-ray beams pass through the chest in the anterior-to-posterior direction, causing the image of the heart to be enlarged (Figure 7-3).

The AP radiograph also often has less resolution and more distortion. Because the patient is often unable to sustain a maximal inspiration, the lower lung lobes frequently appear hazy, erroneously suggesting pulmonary congestion or pleural effusion. Finally, because the AP radiograph is often taken in the intensive care unit, extraneous shadows, such as those produced by ventilator tubing and indwelling lines, are often present (Figure 7-4).

Lateral Radiograph

The lateral radiograph is obtained to complement the PA radiograph. It is taken with the side of the patient’s chest compressed against the cassette. The patient’s arms are raised, with the forearms resting on the head.

To view the right lung and heart, the patient’s right side is placed against the cassette. To view the left lung and heart, the patient’s left side is placed against the cassette. Therefore a right lateral radiograph would be selected to view a density or lesion that is known to be in the right lung. If neither lung is of particular interest, a left lateral radiograph is usually selected to reduce the magnification of the heart. The lateral radiograph provides a view of the structures behind the heart and diaphragmatic dome. It also can be combined with the PA radiograph to give the respiratory care provider a three-dimensional view of the structures or of any abnormal densities (Figure 7-5).

Lateral Decubitus Radiograph

The lateral decubitus radiograph is obtained by having the patient lie on the left or right side rather than standing or sitting in the upright position. The naming of the decubitus radiograph is determined by the side on which the patient lies; thus a right lateral decubitus radiograph means that the patient’s right side is down.

The lateral decubitus radiograph is useful in the diagnosis of a suspected or known fluid accumulation in the pleural space (pleural effusion) that is not easily seen in the PA radiograph. A pleural effusion, which is usually more thinly spread out over the diaphragm in the upright position, collects in the gravity-dependent areas while the patient is in the lateral decubitus position, allowing the fluid to be more readily seen (Figure 7-6).