The chest radiograph (also known as the chest x-ray or CXR) is anecdotally thought to be the most frequently-performed radiological investigation globally although no published data is known to corroborate this. UK government statistical data from the NHS in England and Wales shows that the chest radiograph remains consistently the most frequently requested imaging test by GPs (2019 dataset) 5.
For pediatric chest radiograph see: chest radiograph (pediatric)
On this page:
Indications
The chest radiograph is performed for a broad content of indications, including but not limited to 1-4:
suspected pulmonary embolism
investigation of tuberculosis
follow up of known disease to assess progress
trauma
evaluation of symptoms that could relate to abdominopelvic pathology
thoracic disease processes
monitoring of patients in intensive care units
post-operative imaging
pre-employment medical fitness
immigration screening
check position of nasogastric tubes, endotracheal tubes, PICCs etc.
exclude radiopaque foreign bodies (accidental aspiration, MRI safety screen)
Projections
PA projection
the posteroanterior (PA) view is the standard frontal chest projection
the x-ray beam traverses the patient from posterior to anterior
it is performed standing and in full inspiration with the patient hugging the detector to pull the scapulae laterally
it is the best general radiographic technique to examine the lungs, bony thoracic cavity, mediastinum and great vessels
advantages: technically excellent visualization of the mediastinum and lungs, with accurate assessment of heart size
disadvantages: patient must be able to stand erect
AP projection
the anteroposterior (AP) erect view is an alternative frontal projection to the PA projection with the beam traversing the patient from anterior to posterior
it can be performed with the patient sitting up on the bed and even performed outside the radiology department using a mobile x-ray unit
advantages: more convenient for intubated and sick patients who will not be able to stand for a PA projection
disadvantages: mediastinal structures may appear magnified as the heart is further away from the detector, often poorly inspired, more likely to be rotated and to create skin folds, scapulae often cover some of the lungs
a AP supine view is a further alternative frontal projection technique often used in trauma patients, or patients who can't sit up
the supine position results in physiological widening of the cardiomediastinal outline including superior mediastinum, as well as congestion of the pulmonary veins with upper lobe venous diversion
Lateral projection
the lateral view of the chest is performed erect left lateral and labeled with the side closest to the cassette
a paravertebral gutter technique involves rotating the right side 5-10° anterior (RAO) to align the posterior ribs along the divergent beam
it allows for localization of suspected chest pathology when assessed in conjunction with a PA view
examines the retrosternal and retrocardiac spaces
it allows assessment of the posterior costophrenic recesses
-
salient points
gastric bubble is under the left hemidiaphragm; left hemidiaphragm is less distinct anteriorly due to the cardiac silhouette
right hemidiaphragm appears higher and more complete (as the right is closer to the beam)
the radiation dose from a lateral chest radiograph is substantially higher than that of a PA projection and should probably not be routinely performed for this reason
Additional projections
Other forms of the chest radiographs are performed in a variety of clinical scenarios:
-
the patient is laying either left lateral or right lateral on a trolley on top of a radiolucent sponge.
the detector is placed landscape posterior to the patient running parallel with the long axis of the thorax.
the patient’s hands should be raised to avoid superimposing on the region of interest, legs may be flexed for balance.
problem-solving film, used to differentiate pneumothorax vs. pleural effusion; pneumothorax vs. pneumomediastinum.
air trapping due to inhaled foreign bodies and showing and quantifying pleural effusions
-
for pneumothorax and air trapping due to inhaled foreign bodies
-
right anterior oblique (RAO)/left anterior oblique (LAO) view
for rib fractures and intrathoracic lesions (RAO also used routinely used in barium esophagography)
-
for suspected posterior rib fractures
-
for suspected anterior rib fractures
-
a lateral projection often used to query fractures or infection
-
an RAO projection that is orthogonal to the lateral sternum view
Pitfalls
-
rotation of the frontal projection can markedly affect the appearance of the CXR
apparent mediastinal widening
tracheal deviation
apparent increased thickness of the paratracheal stripes
asymmetric lung density
-
supine positioning of the patient will alter the appearance of the CXR
enlarge the heart (cardiothoracic ratio)
-
alter the appearance of fluid or gas in the pleural space
pneumothorax
pleural effusion
-
alter the appearance of fluid in the lung air spaces
upper lobe vascular redistribution
alveolar fluid distribution
skin folds on AP projections may mimic visceral pleural sign of pneumothorax
think twice before labeling dextrocardia as there exist processing errors; correlate with stomach bubble
Patient preparation
The patient should be asked to remove all clothing and jewelry from the waist up and dress in a hospital gown. Long hair should be worn up.
Tubings and lines must be removed from field of view in ward radiography.
Dosage
The use of low kV (60 - 70 kV) is less effective in demonstrating the lungs behind the heart, diaphragm, and ribs than high kV (120-140 kV). Besides, the use of high kV allows reduction of effective dose to the patient 7,8.
The total effective dose of a chest X-ray (in PA and lateral views) ranges from 0.06 to 0.25 mSv, depending on the voltage of the system used and type of system (film-screen or digital radiography). Meanwhile, PA view accounts for 25% of the total effective dose of a chest X-ray while lateral view accounts for 75% of the total effective dose 6.
