Thorax has always been considered a major hindrance to the diffusion of the ultrasound beam,
due to the air content of the lung and the bone of the thoracic cage.
These limitations prevented for many years the widespread use of ultrasound for diagnosing respiratory diseases,
while conventional radiology and multidetector computed tomography (MDCT) are currently the most used imaging techniques.
In recent years,
the use of ultrasound as a diagnostic tool in the emergency setting has become increasingly popular.
In the critically ill the physical evaluation is of limited usefulness,
while quality of bedside chest radiographs is impaired.
The use of more advanced radiologic technique,
like MDCT,
is not always possible due to the instability of the clinical condition and need to move the patient to different locations.
For these reasons ultrasound has been re-evaluated and gained a growing consensus,
because of its easy handling,
high reproducibility,
bedside feasibility,
cost efficiency and absence of radiation exposure.
The latest developments in bedside lung ultrasound are mainly based on the interpretation of artefacts,
but also direct visualisation of pulmonary structures.
Trans-thoracic ultrasound has become an important diagnostic tool in a number of lung conditions such as pneumonia,
atelectasis,
interstitial syndrome,
pulmonary embolism,
pneumothorax and pleural effusion.
Among them there are traditional applications based on the visualization of real structures,
like diagnosis of pleural effusion and peripheral consolidations,
and new indications based on the detection and interpretation of artefacts,
like diagnosis of pneumothorax and interstitial syndromes.