Antero-posterior View (AP)

The AP view is requested in patients who are too ill to co-operate with the PA film, or who require continued monitoring or treatment. The film is placed behind the patient. Any film labelled ‘mobile’ or ‘resus’ will be an AP view.

Because the x-ray beam diverges as it passes through the chest, and the heart and mediastinum are anteriorly placed, their size is magnified on the film behind. This can interfere with estimation of the size of the heart and the width of the mediastinum.

Sick patients may not be able to sit straight or co-operate with instructions to fully inspire and the resulting films may be rotated, underinspired or miss areas of interest.

Xray: AP view rotated and apices missed (click on the x-ray to enlarge).

Learning bite

The AP film can be technically challenging to obtain and interpret. Uncertainties may be resolved by a departmental film when the patient’s clinical condition allows or alternatively they may require CT.