When we are considering chest skiagrams, PA views are almost always preferred. This is because lung pathologies are better visible in PA view.
Why are lung pathologies “better visible in PA view”?
In AP position the x-ray first enters the heart, so cardiac shadow in AP view is larger than that in PA view. This makes it difficult to find lung lesions behind the enlarged shadow. Please notice the cardiac shadow in the PA and AP chest skiagrams below
But sometimes the condition warrants an AP view. And in that case, the radiologists should be more careful while interpreting the skiagram.
In this article, we shall briefly mention the indications where AP view is done instead of PA view of the chest x-ray.
1. When the person is unable to move
In severe accidental injuries, a person may completely lose the ability to leave his/her bed. Many terminal illnesses literally limit the person to the bed. Immobilization is not uncommon in Intensive Care Units (ICU) of cardiac, burn or surgery departments. In paralysis involving lower part of the body, coma, locked in syndrome, certain musculoskeletal disorders etc. the person becomes unable to move voluntarily…though they can be carried to the radiologist, sometimes it can’t be done without causing further injury to his/her health.
The radiologist can employ portable chest radiograph in these circumstances. The person is kept as upright as possible or supine and the image is taken at full inspiration. It can also be done in semi-supine position (raising the head end of the bed).
The skiagram, in this case, is called a portable film, AP portable chest skiagram or AP mobile projection.
2. In the Operating Room
When an urgent x-ray is needed in the operating room, it can be done using specially designed radiograph or a portable chest radiograph. In this case, also the image may be taken AP.
In the case of children taking a good image while keeping the baby still (without rotation and movement) is a difficult task and sometimes the baby is laid down in supine position for taking the image as prone position increases the distress and thus restlessness too.
Chest Skiagram PA and AP view both images - Case courtesy of Dr Yi-Jin Kuok, Radiopaedia.org. From the case rID: 17910
Dr. Arnab Mukherjee