Chapter 1 Thoracic Radiology
Imaging Methods, Radiographic Signs, and Diagnosis of Chest Disease
EXAMINATION TECHNIQUES AND INDICATIONS
Chest Radiography
Additional views of the chest may be required in special instances (Table 1-1). Shallow oblique radiographs (15 degrees) may be useful in confirming the presence of a suspected nodule. Forty-five-degree oblique radiographs are recommended for the detection of asbestos-related pleural plaques. Apical lordotic views (Fig. 1-2) project the clavicles above the chest, improving visualization of the apices and the middle lobe, particularly in cases of middle lobe atelectasis. Expiration chest radiographs can be used to detect air trapping or to confirm small pneumothoraces. Lateral decubitus radiographs are commonly used to determine the presence or mobility of pleural effusion. These views can also be obtained to detect small pneumothoraces, particularly in patients who are confined to bed and unable to sit or stand erect. Bedside portable examinations may account for up to 50% of chest radiographs obtained for hospital patients.
Table 1-1 Indications for Nonstandard Chest Radiography
Projection | Indications |
---|---|
Oblique | |
Lordotic | Apical and middle lobe disease |
Expiration | |
Lateral decubitus |
Fluoroscopy
Table 1-2 Indications for Chest Fluoroscopy
Technique | Indications |
---|---|
Fluoroscopy | Diaphragmatic movement |
Major airways, trachea |
Computed Tomography
Box 1-1 Common Indications for Computed Tomography
Improvement in scanner technology has led to the introduction of spiral or helical volumetric CT (Box 1-2). These CT scanners acquire data continuously and as the patient is transported through the scanner during a single breath hold (Fig. 1-3). Multidetector helical CT (MDCT) revolutionized thoracic imaging by providing near-isocubic volumetric scanning. Initial multidetector imaging involved four slice detectors that are still popular today. However, this technology has expanded to 16- and 64-slice detectors as well as dual source scanners allowing even shorter scan times. With the newer technology, a patient’s entire thorax is scanned in less than 10 seconds. MDCT slice acquisition provides a thinner slice thickness of an entire original dataset, with the elimination of interscan gaps and minimal respiratory motion. Capabilities include multiplanar imaging with little or no stair-stepping artifact on coronal, sagittal, and three-dimensional images. The greatest impact of MDCT in imaging the thorax involves reconstruction of the vasculature system and airways, and it provides comprehensive imaging of trauma patients (Fig. 1-4). Pulmonary embolism studies are obtained in shorter imaging sessions, improving on motion artifact and resolution of smaller subsegmental vessels.

Figure 1-3 Helical CT scan principle.
(From Kalender WA, Seissler W, Klotz E, Vock P: Spiral volumetric CT with single-breath-hold technique, continuous transport, and continuous scanner rotation. Radiology 176:181–183, 1990).
ANATOMY
Airways
Trachea and Main Bronchi
The trachea is a midline structure that usually is 6 to 9 cm long. The wall contains horseshoe-shaped cartilage rings at regular intervals, but the posterior wall is membranous. The upper limits for coronal and sagittal diameters are 25 and 27 mm for men and 21 and 23 mm for women. The lower limit of normal in both dimensions is 13 mm in men and 10 mm in women. The trachea divides into two major bronchi at the carina. The carinal angle usually is about 60 degrees, but a wide range of 40 to 75 degrees can be seen in normal adults. The right main bronchus has a more vertical course than the left, and its length is considerably shorter. The air columns of the trachea, both major bronchi, and the intermediate bronchus are usually visible on well-exposed standard radiographs of the chest in the frontal projection (Figs. 1-7 and 1-8). The right lateral and posterior walls of the trachea are identifiable on posteroanterior and lateral chest radiographs as vertically oriented linear opacities, called the right paratracheal and posterior tracheal stripes. They are described in more detail in the “Mediastinum” section.
Lobar Bronchi and Bronchopulmonary Segments
Table 1-3 summarizes the bronchopulmonary segments of the right and left lung.
Table 1-3 Bronchopulmonary Segments
Right Lung Segments | Left Lung Segments |
---|---|
Upper Lobe | Upper Lobe |
1. Apical | 1 and 2. Apical posterior |
2. Anterior | 3. Anterior |
3. Posterior | 4. Superior lingula |
Middle Lobe | 5. Inferior lingula |
4. Lateral | Lower Lobe |
5. Medial | 6. Superior |
Lower Lobe | 7 and 8. Anteromedial basal |
6. Superior | 9. Lateral basal |
7. Medial basal | 10. Posterior basal |
8. Anterior basal | |
9. Lateral basal | |
10. Posterior basal |
Pulmonary Vessels
The main pulmonary artery originates in the mediastinum at the pulmonic valve and passes upward, backward, and to the left before bifurcating within the pericardium into the short left and long right pulmonary arteries (Figs. 1-11 and 1-12). The right pulmonary artery courses to the right behind the ascending aorta before dividing behind the superior vena cava and in front of the right main bronchus into a right upper branch (i.e., truncus anterior) and the descending or interlobar branch. The interlobar artery subsequently divides into segmental arteries to the right middle and right lower lobes. The higher left pulmonary artery passes over the left main bronchus. It may give off a separate branch to the left upper lobe or, more commonly, continues directly into a vertical left interlobar or descending pulmonary artery from which the segmental arteries to the left upper and lower lobes arise directly. The left descending or interlobar artery lies posterior to the lower lobe bronchus.
Pulmonary Hila
Computed Tomography
The pulmonary hila are probably best evaluated with CT. They can be visualized with or without the use of intravenous contrast medium. However, dense opacification of the pulmonary or the hilar vessels simplifies interpretation. The bronchial tree is best assessed at wide windows (i.e., 1500 to 2000 Hounsfield units [HU]). Visualization of hilar structures is also improved by thin (2-3 mm) sections. The anatomy of the hila is illustrated in Figure 1-14, and mediastinal anatomy is shown later (see Figs. 1-23 and 1-24).