Radiologic Examination of the Chest

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Radiologic Examination of the Chest

Chapter Objectives

After reading this chapter, you will be able to:

• Describe the fundamentals of radiography.

• Differentiate among the following standard positions and techniques of chest radiography:

• Posteroanterior radiograph

• Anteroposterior radiograph

• Lateral radiograph

• Lateral decubitus radiograph

• Define the following radiologic terms commonly used during inspection of the chest radiograph:

• Air cyst

• Bleb

• Bronchogram

• Bulla

• Cavity

• Consolidation

• Homogeneous density

• Honeycombing

• Infiltrate

• Interstitial density

• Lesion

• Opacity

• Pleural density

• Pulmonary mass

• Pulmonary nodule

• Radiodensity

• Radiolucency

• Translucent

• Describe the three steps to evaluate technical quality of the radiograph.

• Describe the sequence of examination, and include the following:

• Mediastinum

• Trachea

• Heart

• Hilar region

• Lung parenchyma (tissue)

• Pleura

• Diaphragm

• Gastric air bubble

• Bony thorax

• Extrathoracic soft tissues

• Describe the diagnostic values of the following radiologic procedures:

• Computed tomography (CT)

• Positron emission tomography (PET)

• Positron emission tomography and computed tomography scan (PET/CT scan)

• Magnetic resonance imaging (MRI)

• Pulmonary angiography

• Ventilation-perfusion scan

• Fluoroscopy

• Bronchography

• Define key terms and complete self-assessment questions at the end of the chapter and on Evolve.

Key Terms

Radiography is the making of a photographic image of the internal structures of the body by passing x-rays through the body to an x-ray film, or radiograph. In patients with respiratory disease, radiography plays an important role in the diagnosis of lung disorders, the assessment of the extent and location of the disease, and the evaluation of the subsequent progress of the disease.

Fundamentals of Radiography

X-rays are created when fast-moving electrons with sufficient energy collide with matter in any form. Clinically, x-rays are produced by an electronic device called an x-ray tube.

The x-ray tube is a vacuum-sealed glass tube that contains a cathode and a rotating anode. A tungsten plate approximately image-inch square is fixed to the end of the rotating anode at the center of the tube. This tungsten block is called the target. Tungsten is an effective target metal because of its high melting point, which can withstand the extreme heat to which it is subjected, and because of its high atomic number, which makes it more effective in the production of x-rays.

When the cathode is heated, electrons “boil off.” When a high voltage (70 to 150 kV) is applied to the x-ray tube, the electrons are driven to the rotating anode where they strike the tungsten target with tremendous energy. The sudden deceleration of the electrons at the tungsten plate converts energy to x-rays. Although most of the electron energy is converted to heat, a small amount (less than 1%) is transformed to x-rays and allowed to escape from the tube through a set of lead shutters called a collimator. From the collimator the x-rays travel through the patient to the x-ray film.

The ability of the x-rays to penetrate matter depends on the density of the matter. For chest radiographs the x-rays may pass through bone, air, soft tissue, and fat. Dense objects such as bone absorb more x-rays (preventing penetration) than objects that are not as dense, such as the air-filled lungs.

After passing through the patient, the x-rays strike the x-ray film. X-rays that pass through low-density objects strike the film at full force and produce a black image on the film. X-rays that are absorbed by high-density objects (such as bone) either do not reach the film at all or strike the film with less force. Relative to the density of the object, these objects appear as light gray to white on the film.

Standard Positions and Techniques of Chest Radiography

Clinically, the standard radiograph of the chest includes two views: a posteroanterior (PA) projection and a lateral projection (either a left or right lateral radiograph) with the patient in the standing position. When the patient is seriously ill or immobilized, an upright radiograph may not be possible. In such cases a supine anteroposterior (AP) radiograph is obtained at the patient’s bedside. A lateral radiograph is rarely obtainable under such circumstances.

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).

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FIGURE 7-1 Standard posteroanterior chest radiograph with the patient’s lungs in full inspiration.
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FIGURE 7-2 A posteroanterior chest radiograph of the same patient shown in Figure 7-1 during expiration.

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).

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FIGURE 7-3 Compared with the posteroanterior (PA) chest radiograph, the heart is significantly magnified in the anteroposterior (AP) chest radiograph. In the PA radiograph the ratio of the width of the heart to the thorax is normally less than 1 : 2. The reason the heart appears larger in the AP radiograph is that it is positioned in front of the thorax as the x-ray beams pass through the chest in the anterior-to-posterior direction. This allows more space for the heart shadow to “fan out” before it reaches the x-ray film.

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).

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FIGURE 7-4 Anteroposterior (AP) chest radiograph. The diaphragms are elevated, the lower lung lobes appear hazy, the ratio of the width of the heart to the thorax is greater than 2 : 1, and extraneous lines are apparent on the patient’s left side. X-ray examinations using portable machines are frequently performed on patients too ill to be transported to the radiology department. These films, in the best of circumstances, are of poorer quality than erect films taken with standard x-ray apparatus. The films are usually AP projections taken with the x-ray unit in front of and the film plate behind the patient. Overexposure, underexposure, malpositioning, marginal cutoffs, and motion artifacts are often present. In this setting, major events such as partial pneumothoraces, pleural effusions, and infiltrates in dependent parts of the lung may go unrecognized. Therefore careful clinical correlation with the patient’s pathophysiology and symptomatology is imperative.

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).

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FIGURE 7-5 Lateral radiograph. The patient has an overexpanded lung and chest wall (barrel chest deformity) consistent with his known emphysema.

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).

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FIGURE 7-6 Subpulmonic pleural effusion. Right lateral decubitus view. Subdiaphragmatic fluid has run up the lateral chest wall, producing a band of soft tissue density. The medial curvilinear shadow (arrows) indicates fluid in the lips of the major fissure.

Inspecting the Chest Radiograph

Before the respiratory care practitioner can effectively identify abnormalities on a chest radiograph, he or she must be able to recognize the normal anatomic structures. Figure 7-7 represents a normal PA chest radiograph with identification of important anatomic landmarks. Figure 7-8 labels the anatomic structures seen on a lateral chest radiograph.

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FIGURE 7-7 Normal posteroanterior (PA) chest radiograph. 1, Trachea (note vertebral column in middle of trachea); 2, carina; 3, right main stem bronchus; 4, left main stem bronchus; 5, right atrium; 6, left ventricle; 7, hilar vasculature; 8, aortic knob; 9, diaphragm; 10, costophrenic angles; 11, breast shadows; 12, gastric air bubble; 13, clavicle; 14, rib.
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FIGURE 7-8 Normal lateral chest radiograph. 1, Manubrium; 2, sternum; 3, cardiac shadow; 4, retrosternal air space in the lung; 5, trachea; 6, bronchus, on end; 7, aortic arch (ascending and descending); 8, scapulae; 9, vertebral column; 10, diaphragm; 11, breast shadow.
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