Out of field artifact

Out of field artifact (also known as incomplete projection artifact) is due to part of the patient existing peripheral to the field of view of the CT scanner. This can be a particular issue in obese patients who only just fit within the scanner bore.

The lack of data from these out of field tissue/objects interferes with the ability of the software to generate a correct image leading to streaking, and areas of unusual increased or decreased density. At best this is a mere annoyance, at worst it may render the images uninterpretable.

A contributing factor, especially in obese patients, may be the obstruction of reference channels of the x-ray detectors, which can also produce streaking artifact.

Preventing this artifact relies on the CT operator ensuring that the body of the patient lies wholly within the scan field or - in the case of the arms - place them up or down depending upon whether the head and neck or chest and body are being scanned.