In medical terms, an artifact is any distortion, error, or false finding in a diagnostic test that doesn’t reflect what’s actually happening in your body. Artifacts can appear in imaging scans, heart tracings, blood work, and pathology slides. They’re not signs of disease, but they can mimic disease, hide real problems, or make results harder to interpret. Understanding what causes them helps explain why a doctor might order a repeat test or ask you to hold still during a scan.
Why Artifacts Matter for Your Diagnosis
Artifacts can lead to three outcomes, all of them problematic. A false positive means something looks abnormal when it isn’t, potentially triggering unnecessary follow-up tests or treatment. A false negative means a real problem gets hidden, delaying diagnosis. And sometimes artifacts simply make a result ambiguous, forcing a repeat test or a different imaging approach.
Radiologists, cardiologists, and lab technicians are trained to spot artifacts and distinguish them from genuine findings. But recognition isn’t always straightforward, especially when an artifact closely resembles a known disease pattern. This is one reason second opinions and repeat testing exist.
Imaging Artifacts: MRI, CT, and Ultrasound
Medical imaging is where artifacts show up most visibly, and each type of scan has its own characteristic distortions.
MRI Artifacts
MRI scans are particularly sensitive to movement and metal. Breathing, heartbeats, blood flow, and even the pulsing of spinal fluid can create “ghost” images, which are faint duplicate signals that overlay the real anatomy. Technicians reduce these by asking you to hold your breath, using cardiac or respiratory gating (syncing the scan to your heart or breathing cycle), or choosing faster imaging sequences.
Metal is the biggest source of MRI artifacts. Surgical clips, joint replacements, dental hardware, and even tattoo ink or metallic makeup can warp the magnetic field and distort the image. The result is usually a dark void or a bright flare around the metal object that obscures nearby tissue. Certain scan sequences produce worse metal distortion than others, so technicians adjust their approach when they know metal is present.
CT Scan Artifacts
CT scans use X-rays, and metal objects cause a different kind of problem here: bright and dark streaks radiating outward from the metal. These streaks are caused by a combination of beam hardening (the X-ray beam changing energy as it passes through dense material), photon starvation (not enough X-rays getting through), and scatter. If you have metal implants, screws, or dental fillings, you may see these streaks on your CT images.
Modern CT scanners offer built-in software to reduce metal artifacts. These algorithms work by identifying the corrupted data in the scan, removing it, and filling in estimated corrected values. Several commercial versions exist across scanner manufacturers, and they all follow a similar principle: segment the metal from the surrounding tissue, calculate what the image should look like without the distortion, and reconstruct a cleaner picture. Newer approaches combine these traditional correction methods with deep learning, where AI trained on thousands of scans further improves image quality. A 2025 study on patients with metal coils in treated brain aneurysms found that combining deep learning reconstruction with metal artifact reduction at specific energy levels produced the best balance between reducing artifacts and clearly displaying blood vessels.
Ultrasound Artifacts
Ultrasound artifacts stem from how sound waves interact with different tissues. Some of these are actually useful. Acoustic shadowing, a dark area behind a dense object like a kidney stone or gallstone, helps confirm the object is solid. Enhancement, a brighter area behind a fluid-filled structure like a cyst, confirms it contains liquid. Doctors use these artifacts as diagnostic clues rather than treating them as errors.
Other ultrasound artifacts are genuinely misleading. A mirror image artifact makes structures on one side of a strong reflector (like the diaphragm) appear duplicated on the other side. Reverberation artifacts create repeated echoes that look like layered lines. Comet tail artifacts produce bright streaks trailing behind small, highly reflective objects. Recognizing these patterns prevents misinterpretation.
ECG and Heart Monitor Artifacts
Electrocardiograms (ECGs) record the heart’s electrical activity through electrodes on the skin, and they’re easily disrupted. The most common culprit is motion. Muscle tremors from shivering, anxiety, Parkinson’s disease, or even just moving your arms during the test send electrical signals that get picked up alongside the heart’s signal. When skeletal muscles are shaking, the ECG tracing gets “bombarded” by apparently random electrical activity that can obscure the heart rhythm entirely.
These motion artifacts can closely mimic serious heart conditions. A sudden movement of a limb during recording can look like a premature heartbeat. Sustained tremor can resemble certain arrhythmias. Incorrect electrode placement is another common source. If electrodes are placed on the wrong spots or their cables are swapped, the resulting tracing can look like a heart attack, a conduction problem, or a rhythm disorder when none exists.
Electrical interference from nearby equipment, poor grounding, or alternating current systems can also contaminate the signal. This shows up as a regular, fine oscillation on the tracing. Filters built into modern ECG machines catch most of this, but older or poorly maintained equipment may not.
Lab Work and Blood Test Artifacts
Artifacts in blood tests are less visible but just as consequential. The most common example involves potassium levels. Potassium lives primarily inside your cells, and if blood cells break open (a process called hemolysis) during collection or handling, the potassium spills into the sample and artificially inflates the measured level. This can make it look like you have dangerously high potassium when your actual levels are normal.
Several things trigger hemolysis: drawing blood through a needle that’s too small, shaking the sample tube too vigorously, or leaving a tourniquet on for more than about a minute, which causes blood to pool and cells to rupture. Even the order in which blood collection tubes are filled matters. If the sequence is wrong, additives from one tube can contaminate the next, skewing results. Between 4% and 32% of all laboratory errors happen during the actual analysis of the sample, but many more occur during collection and transport.
Elevated white blood cell or platelet counts can also falsely raise potassium readings when those cells break down in the sample tube. This is why labs flag hemolyzed samples and often request a redraw rather than reporting potentially misleading numbers.
The Five Main Causes of Artifacts
Across all types of medical testing, artifacts generally fall into five categories:
- Patient-related: Movement, breathing, body habitus, anxiety, or tremor during testing.
- Equipment-related: Malfunctioning machines, uncalibrated sensors, or electrical interference.
- Technical: Incorrect settings chosen by the operator, wrong imaging sequences, or improper sample handling.
- Material-related: Metal implants, prostheses, foreign bodies, or contaminated lab tubes.
- Treatment-related: Prior surgeries, implanted devices, medications, or supplemental oxygen affecting scan signals.
What Happens When an Artifact Is Found
When a radiologist, cardiologist, or lab technician identifies an artifact, the next step depends on how much it affects the results. Sometimes the artifact is minor and clearly identifiable, and the reading physician simply notes it in the report and interprets around it. Other times, it obscures the area of interest, and you’ll be asked to repeat the test, possibly with different settings or a different imaging approach.
For imaging, this might mean switching to a scan sequence less sensitive to metal, using software correction, or simply repositioning you on the table. For an ECG, it could mean warming you up if you’re shivering, replacing a loose electrode, or waiting until tremor subsides. For blood work, it typically means a new blood draw with careful attention to collection technique.
If your test report mentions an artifact, it doesn’t mean something went wrong in a dangerous sense. It means the interpreting physician noticed a distortion, flagged it, and accounted for it in their reading. In some cases, it’s the reason a follow-up test gets ordered, not because something suspicious was found, but because the first image wasn’t clean enough to give a confident answer.