Chest X-ray quality

Inspiration and lung volume

Chest X-rays are conventionally acquired in the inspiratory phase of the respiratory cycle. The radiographer asks the patient to, 'breathe in and hold your breath!' Patients who are short of breath, or those who are unable to follow the instructions may find this difficult.

When interpreting a chest X-ray it is important to recognise if there has been incomplete inspiration. If the image is acquired in the expiratory phase, the lungs are relatively airless and their density is increased. Also, the raised position of the diaphragm leads to exaggeration of heart size, and obscuration of the lung bases.

Assessing inspiration

To assess the degree of inspiration it is conventional to count ribs down to the diaphragm. The diaphragm should be intersected by the 5th to 7th anterior ribs in the mid-clavicular line. Less is a sign of incomplete inspiration.

Key points

  • Always assess inspiration and lung volumes
  • Incomplete inspiration can lead to exaggeration of lung markings and heart size
  • Lung hyperexpansion is a sign of obstructive lung disease
Hover over image to show findings

Expiration

  • (Same patient as next image)
  • Anteriorly only the third rib intersects the diaphragm at the mid-clavicular line
  • The lung bases are white - Is there consolidation?
  • How big is the heart?
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Hover over image to show findings

Inspiration

  • (Same patient as previous image)
  • Anteriorly the sixth rib intersects the diaphragm at the midclavicular line
  • The lungs are not consolidated
  • The heart size is clearly normal
Click image to align with the top of the page

Assessing for hyperexpansion

While checking for adequate inspiration you may notice that a patient's lungs are hyperexpanded (>7th anterior rib intersecting the diaphragm at the mid-clavicular line). This is a sign of obstructive airways disease.

It is possible to assess for hyperexpansion by counting ribs, or by checking for flattening of the hemidiaphragms.

Hover over image to show findings
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Normal expansion

This patient has taken a good breath in such that the diaphragm is intersected by the 6th rib in the mid-clavicular line.

The hover over image shows an imaginary line (dotted) between the costophrenic and cardiophrenic angles. The distance between this line and the diaphragm (green line) should be greater than 1.5cm(asterisk) in normal individuals. In practice this is rarely measured and a quick assessment of diaphragm shape is all that is necessary.

Hover over image to show findings
Click image to align with the top of the page

Hyperexpansion

It is often quicker to assess for hyperexpansion by looking at the hemidiaphragms. These are clearly flattened (red line) in this patient.

The ribs are difficult to count as they have lost density. This is due to long term steroid treatment for the patient's emphysema.

There is also consolidation of the lung bases due to pneumonia.

 

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