The chest radiograph is the most frequently performed radiographic study in the United States. It should almost always be the first radiologic study ordered for evaluation of diseases of the thorax. The natural contrast of the aerated lungs provides a window into the body to evaluate the patient for diseases involving the heart, lungs, pleurae, tracheobronchial tree, esophagus, thoracic lymph nodes, thoracic skeleton, chest wall, and upper abdomen. In both acute and chronic illnesses, the chest radiograph allows one to detect a disease and monitor its response to therapy. For many disease processes (eg, pneumonia and congestive heart failure) the diagnosis can be established and the disease followed to resolution with no further imaging studies. There are limitations to the chest radiograph, and diseases may not be sufficiently advanced to be detected or may not result in detectable abnormalities. Other imaging methods are needed to complement the conventional chest radiograph. These imaging methods include computed tomography (CT), positron emission tomography/computed tomography (PET/CT) and other radionuclide studies, magnetic resonance (MR) imaging, and ultrasound (US). These techniques, their clinical uses, and case studies are included in this chapter.
The Posteroanterior and Lateral Chest Radiograph
The simplest conventional study of the chest is a posteroanterior and lateral chest radiograph taken in a radiographic unit specially designed for these studies. The x-rays travel through the patient and expose a receptor from which the image is recorded. Most commonly, digital receptors are used, although a receptor utilizing an intensifying screen and radiographic film remains in some use as well. Computed radiography and large field-of-view image intensifiers are two types of digital receptors. The digital images may be printed on film by laser printers but are generally viewed on monitors. The two views of a chest radiograph are taken in projections at 90 degrees to each other with the patient's breath held at the end of a maximum inspiration. The first view is obtained as the patient faces the receptor with the x-ray beam source positioned 6 feet behind him. Because the x-ray beam travels in a posterior-to- anterior direction, this view is called a posteroanterior (PA) chest radiograph. Another view is then obtained with the patient turned 90 degrees and the left side against the receptor and arms overhead. The x-ray beam travels from right to left through the patient, and this is called a left lateral view. Anatomic features of the chest that are readily identifiable on conventional radiographs are shown in Figures 4-1 and 4-2.
(A–C) Normal radiographic anatomy. Posteroanterior chest radiographs. a, aorta; ajl, anterior junction line; apw, aortopulmonary window; ca, carina; cap, cardiophrenic angle; cl, clavicle; cpa, costophrenic angle; ...