Artifact on an imaging test is something that is not really present on the image but related to the machine taking the images or something external to the patient like clothing, hair, devices, skin folds, etc. The reason this is important is that the interpreting radiologist needs to be able to not confuse an artifact for a real abnormality. Sometimes this is not possible and either repeat imaging or additional testing is needed.
One of the more common artifacts I see is related to patient motion. Most imaging exams require you to be very still during the exam and at times hold your breath. Not every patient is able to hold still or control their breath holds. This results in blurry and distorted images which can hide abnormalities.
Some artifacts can mimic life threatening abnormalities. For example, I sometimes see skin folds on chest X-ray mimicking a pneumothorax or collapsed lung. I see artifacts mimicking a clot to the lung or pulmonary embolus on CT scans. I see artifacts mimicking an aortic dissection or tear of the blood vessel on CT scans done for chest pain because of heart motion. Both experience of the radiologist, modified technique and repeat exams can be done to resolve the uncertainty.
Some artifacts are related to objects external to the patient. For example, some devices like pacemakers can cause artifacts which block the view or nearby structures. On a bone X-ray of the hand, a ring can block the view of a portion of the bone if not removed. On a chest X-ray, hair can overlap the lungs and mimic or hide abnormalities. Even contrast administered on CT scans can cause artifact near vessels in the chest and block the view of adjacent structures.
The radiologist will frequently describe artifacts and their resulting limitations in the radiology report. In some cases, he may not be able to tell whether it is artifact or true abnormality. In those cases, the radiologist will recommend another test or repeat imaging.
Sometimes the artifact will prevent a certain condition from being excluded. An example of this is a CT done to exclude a clot to the lung or pulmonary embolism. When the blood vessels aren’t as bright as they should be or the patient isn’t holding their breath the test can become inadequate to exclude an abnormality. In these cases, you may need a repeat test since this can be life threatening.
Artifacts are frequently seen on imaging tests of all types. Thankfully, optimizing imaging techniques and having experienced board certified radiologists interpret imaging tests helps to identify artifacts for what they are. Often the radiologist will indicate the limitations that artifacts cause, whether the test needs to be repeated, or whether a finding may be an artifact and further testing is needed.