Chest radiography is the most commonly ordered imaging test in
emergency department patients. It can provide considerable diagnostic
information for a wide variety of thoracic disorders. Its diagnostic
capabilities are based largely on the contrast between the air-filled
lungs and pathological processes that cause fluid accumulation within
Although chest CT provides greater
anatomical detail of the pulmonary parenchyma and is often used
in non-emergency patients with pulmonary disease, the use of chest
CT in the ED is limited to certain critical conditions that do not
produce distinctive findings on conventional radiography. These
include pulmonary embolism and aortic dissection. CT is also used
in ED patients with major chest trauma to detect an aortic injury,
pneumothorax, hemothorax and pulmonary contusions that may not be
evident on the supine portable chest radiographs.
In general, a diagnostic test should be ordered when the disease
under consideration produces characteristic findings which help
confirm or exclude the suspected disorder. A number of approaches
can be used in deciding to order a radiograph.
With a simplistic “geographic” approach, radiographs
are obtained of the region where the patient is having symptoms,
e.g., a chest radiograph in a patient with chest pain. Such an approach
is ill-advised because it can lead to diagnostic errors, as well
as excessive and unnecessary testing.
Using a symptom-based approach to
radiograph ordering, the decision to obtain radiographs is based
on characteristics of the patient’s symptoms, for example
whether the chest pain is severe or mild, pleuritic or pressure-like
However, a more rational diagnosis-based
approach is to first consider the potential disorders that
might be present and then to obtain radiography if the suspected
disorder has characteristic radiographic findings, such as pneumonia
and pneumothorax. This approach is the most likely to yield clinically
useful information and to avoid unnecessary testing. Determining
which disorders need investigation in an individual patient is ultimately
based on the clinical judgment, knowledge and experience of the
Two perpendicular views should be obtained whenever possible.
The preferred frontal view is a postero-anterior view (PA view). This view is obtained in
the radiology suite with the patient standing and the imaging cassette placed
against the patient’s anterior chest wall. The x-ray beam
is directed horizontally and traverses the patient from posterior
to anterior. The patient’s hands are positioned on the
hips, which moves the scapulae laterally and away from the lungs.
The patient is instructed to take a full inspiration. The PA view
is preferred because the heart and mediastinum are closest to the
x-ray imaging cassette and therefore less distorted by magnification.
When the patient is too ill or debilitated to stand for a PA
view, an antero-posterior view (AP view) is
obtained. The patient is in either a lying or sitting position.
The sitting position is preferred whenever possible. The x-ray beam
is directed downward towards ...