An artifact in medicine is any distortion, error, or false signal in a diagnostic test that doesn’t reflect what’s actually happening in your body. Artifacts can appear on imaging scans, heart tracings, blood work, and virtually any other medical test. Some are harmless annoyances that slightly blur an image. Others are dangerous mimics that look exactly like a real disease, potentially leading to a wrong diagnosis or unnecessary treatment.
Understanding what causes artifacts matters because they’re extremely common. Recognizing them helps clinicians avoid false diagnoses, and knowing what triggers them can help you as a patient avoid the most preventable ones.
How Artifacts Differ From Real Findings
A true medical finding reflects something biological: a tumor, an irregular heartbeat, an elevated blood chemical. An artifact reflects something technical: the equipment malfunctioned, the patient moved, or the sample was handled improperly. The tricky part is that artifacts can be convincing. A truncation artifact in a spinal MRI, for example, can look like a fluid-filled cavity in the spinal cord. The same type of artifact in a knee MRI can mimic a torn meniscus. In both cases, the “abnormality” exists only in the image, not in the patient.
This is why radiologists, cardiologists, and lab technicians spend significant training time learning to spot artifacts. When a test result doesn’t match the clinical picture, an artifact is one of the first things to consider.
Artifacts in MRI Scans
MRI is particularly prone to artifacts because the technology relies on precise magnetic fields and radio signals. Disruptions come from two broad sources: the scanner hardware itself and the interaction between the scanner and the patient’s body.
Metal is the biggest offender. Surgical clips, joint replacements, dental implants, embolization coils, and even intraorbital metal fragments can all warp the magnetic field and create bright or dark distortions in the image. But it’s not just implants. Makeup containing metallic pigments, tattoo ink, hairbands, and clothing with metal snaps or zippers can all produce artifacts. This is why MRI technicians ask you to remove jewelry and change into a gown before scanning.
Truncation artifacts are another common MRI issue. They show up near sharp boundaries between tissues of very different brightness, appearing as alternating bright and dark lines, sometimes called “ringing.” These lines can be mistaken for structural damage that isn’t there.
Patient movement during a scan is a persistent problem as well. Because MRI acquires data over several minutes, even small movements disrupt the spatial alignment of the image. Breathing, swallowing, or shifting position can all introduce blurring or ghosting, which is why you’re asked to stay perfectly still and sometimes hold your breath during certain sequences.
Artifacts in CT Scans
CT scanners use X-ray beams, and the most well-known CT artifact is beam hardening. CT reconstruction assumes that X-rays are all the same energy level, but in reality, the beam contains a spectrum of energies. When that beam passes through dense material, especially metal, the lower-energy photons get absorbed first, “hardening” the beam. This mismatch between what the scanner expects and what actually happens produces dark streaks and bands radiating outward from the dense object.
Metal implants are the classic culprit. Hip replacements, spinal hardware, and dental fillings can all generate dramatic streak artifacts that obscure the surrounding tissue. But beam hardening also happens to a lesser degree with dense bone, particularly at the base of the skull where thick bone surrounds the brain.
Beam-hardening artifacts fall into two categories: cupping artifacts, where the edges of a round object appear brighter than the center, and streaking artifacts, which are the dark lines between two dense objects. Scattered radiation, noise, and partial volume effects (where a single pixel covers two different tissue types) add further distortion.
Artifacts in ECG (Heart Tracings)
Electrocardiograms record tiny electrical signals from the heart, which makes them vulnerable to interference from almost any other electrical activity nearby. ECG artifacts fall into a few major categories.
Motion artifacts are the most common. Any rhythmic shaking, whether from Parkinson’s disease, anxiety tremors, shivering from cold or fever, or simply a patient moving their arms during the test, sends bursts of electrical activity from skeletal muscles into the recording. This muscle noise can look like irregular heart rhythms. Sudden limb movements may mimic premature contractions or even appear as dangerous arrhythmias, potentially triggering unnecessary alarm.
Electrical interference is the other major source. Nearby electronic devices, fluorescent lights, electrical beds, and even cell phones within about 25 centimeters of the ECG sensor can introduce a steady oscillation into the tracing. This type of interference, sometimes called 60-cycle artifact (after the frequency of alternating current in the power grid), creates a fuzzy, thickened baseline that obscures the heart’s actual signal. Turning off nearby devices and ensuring the ECG machine’s filters are working properly usually resolves it.
Baseline wander, where the tracing slowly drifts up and down, typically comes from the patient breathing deeply or from electrodes that aren’t making good contact with the skin. Dry skin, oily skin, or loose electrode pads can all contribute.
Artifacts in Blood Tests
Lab artifacts are especially consequential because they produce concrete numbers that may drive treatment decisions. Potassium levels are a prime example. Falsely elevated potassium, called pseudohyperkalemia, is one of the most common lab artifacts, and it usually happens before the blood ever reaches the analyzer.
The causes start at the moment of collection. Leaving a tourniquet on for more than a minute causes blood to concentrate and red blood cells to break open, a process called hemolysis. Clenching your fist during a blood draw releases potassium directly from forearm muscles into the sample. Traumatic needle insertion, using the wrong needle size, or drawing blood too forcefully through a syringe can all rupture red blood cells, spilling their intracellular potassium into the surrounding fluid and artificially inflating the result.
Sample handling after collection matters just as much. Shaking the tube too vigorously, spinning it in a centrifuge at excessive speed, or re-centrifuging a gel separator tube can all damage cells. If the antiseptic swab used before the needle stick contains ethanol and isn’t allowed to dry completely, that solution can enter the bloodstream and rupture cell membranes on contact.
Even the order in which blood tubes are filled matters. If a tube containing certain additives (like the anticoagulants used in purple-top or gray-top tubes) is drawn before the tube for potassium testing, trace amounts of those additives can carry over and artificially raise the potassium reading.
Temperature and Storage
Cold temperatures inhibit the cellular pump that normally keeps potassium inside cells, allowing it to leak out and raise measured levels. High temperatures initially lower potassium, then raise it as cells exhaust their energy supply and the pump fails entirely. Blood specimens should not be stored between 2°C and 8°C, or left above room temperature for more than 24 hours, to avoid these shifts.
Patient-Related Causes Across All Tests
Some artifact sources are universal regardless of the test. Body movement is the most pervasive: it degrades MRI images, creates false ECG signals, and can even affect blood draws if a patient jerks during collection. For imaging specifically, body size plays a role. Larger body habitus requires X-rays or signals to travel through more tissue, which increases noise and can produce artifacts that wouldn’t appear in a smaller patient.
Metal in the body affects nearly every imaging modality. In MRI, it warps the magnetic field. In CT, it causes beam hardening and streaks. Even in plain X-rays, metal can obscure the anatomy behind it. Patients with significant hardware, such as spinal fusion rods or total joint replacements, often need specialized imaging techniques to work around these artifacts.
How Artifacts Are Minimized
Prevention depends on the type of test. For imaging, the most straightforward strategy is reducing motion. Technologists coach patients to hold still, time scans to breathing cycles, and sometimes use faster imaging sequences that are less sensitive to movement. Sedation may be necessary for patients who can’t remain still, such as young children or people with certain neurological conditions.
Removing all metal before an MRI is standard protocol. For metal that can’t be removed, like implants, radiologists use specialized pulse sequences designed to reduce metal-related distortion. In CT, software-based metal artifact reduction algorithms can partially reconstruct the image data that metal streaks have corrupted.
For ECGs, good skin preparation (cleaning oily or dry skin so electrodes stick firmly), ensuring the patient is warm and relaxed, and turning off unnecessary electronics in the room all reduce interference. For blood work, proper phlebotomy technique is the single most important safeguard: using the correct needle gauge, limiting tourniquet time, following the recommended tube order, and handling samples gently during transport and processing.
In every case, the most powerful tool against artifacts is awareness. When a clinician recognizes that a finding could be artifactual rather than real, they can repeat the test, adjust the technique, or correlate with other clinical information before making a diagnosis.