Chest radiograph

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)

Indications

The chest radiograph is performed for a broad content of indications, including but not limited to ^1-4:

• respiratory disease

• cardiac disease

• hemoptysis

• suspected pulmonary embolism

• investigation of tuberculosis

• pneumonia

• pneumothorax

• suspected metastasis

• follow up of known disease to assess progress

• chronic dyspnea

• trauma

• pneumoperitoneum

• 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)

• skeletal survey

Routine pre-operative chest radiographs are of no value unless there are indications as above or the patient is expected to require intensive care following surgery.

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 usually 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 more complete

  • consider which side is closest to the image receptor (IR) i.e. a left or right lateral; the side further away from the IR will appear more magnified

  • 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:​

• lateral decubitus

  • 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 upper limbs 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

• expiration view

  •  for pneumothorax and air trapping due to inhaled foreign bodies

• lordotic/apical view

  • demonstrates areas of the lung apices that appear obscured on the PA/AP chest radiographic views

  • projects the clavicles superior to the lung apices

• prone view

  • when the patient cannot lie supine

• right anterior oblique (RAO)/left anterior oblique (LAO) view

  •  for rib fractures and intrathoracic lesions (RAO also used routinely used in barium esophagography)

• ribs AP view

  • for suspected posterior rib fractures 

• ribs PA view

  • for suspected anterior rib fractures 

• sternum lateral view 

  • a lateral projection often used to query fractures or infection

• sternum oblique view 

  • 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

• cardiothoracic ratio

  • can only be accurately determined on a PA erect radiograph with full, suspended inspiration ⁹

  • unable to determine true heart enlargement versus heart magnification if patients are imaged

    • in AP or supine projection

    • in PA erect projection with insufficient inspiration

• supine positioning of the patient will alter the appearance of the CXR

  • 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.