Overview
The projection of the chest x-ray refers to the direction that the x-rays travel through the body. This is determined by the placement of the x-ray generator and the x-ray plate.
Different projections are used in various clinical situations, and can affect the interpretation of the x-ray.
Posterior-Anterior (PA)
In order to take a PA film, the x-ray plate is placed in front of patient, with the beam travelling from posterior to anterior.
The PA film is the most common film, and is usually only taken in X-ray departments.
Example
- A PA film - note the normal mediastinal size.
![A PA film - note the normal mediastinal size.]()
Anterior-Posterior (AP)
In order to take an anterior-posterior film, the x-ray plate is placed behind the patient, resulting in enlargement of the mediastinum.
This type of film is usually taken in acute / critical care settings, where a patient is sitting up in bed and the plate can be placed behind them.
Example
- An AP film - note the artificially enlarged mediastinum.
![An AP film - note the artificially enlarged mediastinum.]()
Lateral
In order to take a lateral film, the x-ray plate is placed beside the patient.
A lateral film provides a side view of the chest - this is especially useful for identifying a lobe affected by consolidation.
Example
- A lateral chest xray demonstrating right middle lobe consolidation.
![A lateral chest xray demonstrating right middle lobe consolidation.]()
Overview
On an AP or PA film, don't comment on specific lobes of the lung as the lobes overlap. Instead refer to the right / left upper, middle and lower zones.
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