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Lung Ultrasound

Lung Ultrasound
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Overview

Probe Selection

The linear and curvilinear probes are used for lung ultrasound scanning.

  1. Linear probe: Use this to scan to a depth of 6cm. It provides for good resolution of the pleural line and superficial structure.
  2. Curvilinear probe: Use this particularly at the lung bases and for deeper imaging. It is useful for evaluating consolidation, B-lines and pleural effusions. 

Patient Position

The patient is scanned in the supine position or head up at 45 degrees.

Protocol

Each hemithorax can be divided into 4 zones as shown in image 1.

Scan these 4 zones with the linear and curvilinear probe.

The probe should be place in the longitudinal plane, across 2 ribs. The probe orientation marker faces the patient’s head.

Probe positioning. The transducer orientation marker faces the patient's head and the probe is placed longitudinally across 2 ribs.
Image 1

Picture

Images 2 and 3 show the normal lung ultrasound scan obtained with a linear probe.

Note the batwing sign. The ribs are seen, along with rib shodows. The subcutaneous and intercostal muscles between the ribs are see.

The pleural line is seen as a bright echogenic line. In normal lungs, it has the appearance of “ants marching” and appears to shimmer. This appearance is called normal lung sliding.

A-lines are artefacts that are seen in well aerated lungs. They are caused by reflection of ultrasound waves between the probe head and the reflective pleura. They appear at equidistant intervals in well aerated lungs.

Image 2
Image 3

The images below are obtained with a linear probe and curvilinear probe. They demonstrate normal lung sliding and A-lines.

Normal Lung Sliding: Observe the ants marching appearance of the pleural line. Linear probe
Normal Lung Sliding. Image is obtained with a curvilinear probe. The pleural line is seen at the top. A lines (A1, A2 and A3) appear in normal well aerated lungs. They are artefacts caused by reflection of the ultrasound waves between the probe and reflective pleura.

The lung bases are scanned with a curvilinear probe. The right and left lower anterior lateral zones are shown below. The curtain sign is seen in normal well aerated lungs at the bases.

Image is obtained at position 4. This is the lung base and a curvilinear probe is used.
Image is obtained at the left lung base with a curvilinear probe.
Image shows the right lung base. In a well aerated lung, the curtain sign is seen. The image is lost during inspiration as air in the lungs do not transmit ultrasound waves. Note the disappearance of the spine during inspiration. In the presence of a pleural effusion or consolidation, the curtain sign is not seen. Instead the spine is clearly visualised throughout the respiratory cycle. This is because fluid transmits ultrasound waves well.