The short answer: Movement blurs MRI pictures or adds faint "ghost" copies, so the technologist usually repeats the affected series. You are not in danger. In a 2015 University of Washington study, 19.8% of MRI exams included at least one repeated sequence. A small shift costs a few minutes. Large or constant movement can mean rescheduling.
Why is MRI so sensitive to motion?
An MRI picture is not a snapshot. The scanner collects raw signal piece by piece over a stretch of time, then a computer assembles it into an image. Physicists call that raw data space "k-space." If your body shifts halfway through, the early pieces and the late pieces no longer describe the same position, and the math cannot line them up cleanly.
That collection takes a while. MedlinePlus notes a full exam usually lasts 30 to 60 minutes, and it is built from several separate series. The National Institute of Biomedical Imaging and Bioengineering (NIBIB) puts it plainly: you must remain very still during imaging so the image does not blur.
The scale is small. A 2017 narrative review in Frontiers in Neurology reports that even healthy, cooperative adults make spontaneous head movements of up to a millimeter. The same review notes that higher-resolution scans are more sensitive to motion, and they often take longer, which makes the problem worse.
What do motion artifacts look like on the images?
The two classic patterns are blurring and ghosting, according to the Frontiers review. Blurring softens edges, so the outline of an organ or a small spot looks smeared. Ghosting shows up as faint repeated copies of a structure stacked across the picture in one direction. A 2015 review in the Journal of Magnetic Resonance Imaging calls bulk patient motion one of the most frequent sources of artifacts in clinical MRI.
The timing of the movement matters. The Frontiers authors explain that on scans that fill k-space in a simple line-by-line order, artifacts cluster according to when the motion happened. Sometimes a single slice becomes unreadable while the rest is fine.
Blur is not only cosmetic. In a 2019 study of 334 breast lesions, radiologists caught cancers less often when motion artifacts were heavier, although lesion size and type mattered most. Small findings are the first to be lost.
Will the scan have to be repeated or rescheduled?
Usually only the spoiled series is redone, while you are still on the table. The technologist reviews images during the exam and can run a sequence again. In the University of Washington review of 192 exams, significant motion artifacts appeared in 7.5% of outpatient exams and 29.4% of inpatient or emergency exams. Repeats are routine, not a failure.
Repeats do add time. The same study estimated that motion cost the hospital about $592 per hour of scanner time in lost revenue, or roughly $115,000 per scanner per year. That is a hospital cost, not a bill sent to you. Our guide on how long an MRI takes explains how repeats stretch the appointment.
Rescheduling is less common. It happens when someone cannot lie still at all, for example because of severe pain, confusion, or anxiety. RadiologyInfo.org says image quality suffers when a patient is anxious, confused, or in severe pain, and that patient movement has the same effect.
Which scans and patients are most affected by movement?
- Chest and abdomen. The Frontiers review notes the diaphragm moves several centimeters with each normal breath. That is why body MRI uses breath-holds. RadiologyInfo.org warns that if you cannot hold your breath, some exams will be blurry.
- Neck and spine. Swallowing moves the throat. Technologists often place a "saturation band" over the throat to block that signal, per the same review.
- Heart. Cardiac motion exceeds 1 centimeter, so heart scans are timed to the heartbeat.
- Brain. Small head movements matter most on detailed or functional scans. Cushions and straps help.
- Children. NIBIB says getting a clear image is especially hard in children, and many young children need anesthesia. A 2020 AJR review describes newer motion-reduction methods that may cut the need for sedation.
- Hospital patients. Inpatients had about four times the rate of serious artifacts seen in outpatients in the 2015 study.
What if you need to cough, sneeze, or scratch?
A single quick movement usually spoils only the series running at that moment. Because artifacts cluster around the time of the motion, a brief cough often means one sequence is repeated, not the whole exam. A slow drift, or repeated fidgeting, is harder to fix.
If you feel a cough or an itch building, wait for a quiet gap between series if you can. Technologists usually tell you when a series starts and how long it will run. If you cannot wait, use the call button or speak up. NIBIB lists holding a panic button as a standard way patients stay in control. Telling the technologist is better than a hidden shift, because they can restart the right series.
If nerves are the reason you fidget, our page on MRI claustrophobia covers coping strategies, and anxiety.md covers anxiety more broadly. If you expect to need medicine to relax, read about MRI sedation and getting home.
How can you hold still? A checklist
These steps build on the practical advice in the Frontiers review, RadiologyInfo.org, and MedlinePlus.
- Get comfortable before the first series. The review stresses comfortable positioning. Ask for a knee wedge, a blanket, or more padding now, not ten minutes in.
- Accept the cushions and straps. They are not restraints. They make small head drift less likely.
- Practice the breath-hold. For body scans, ask the technologist to run through the instruction once. Hold exactly when told, for as long as asked.
- Relax your jaw and swallow between series. Swallowing moves the neck. Try to swallow when the noise stops.
- Close or cover your eyes, or ask for music. NIBIB lists both as ways patients stay settled in the scanner.
- Speak up early. Pain, cold, or panic gets worse with time. Ask for help before it turns into movement.
- Ask about relaxing medicine if you cannot lie still. MedlinePlus notes it may be offered to people who have difficulty lying still or are very nervous.
How do technologists and newer scanners reduce motion effects?
No single fix works for every scan. The 2015 JMRI review describes a "toolbox" of methods, each good for some situations. Common tools include faster sequences, breath-hold and breathing-triggered scans, and timing to the heartbeat. Saturation bands are another tool.
Some sequences collect data in a rotating "propeller" pattern. According to the Frontiers review, this repeatedly samples the center of k-space so the computer can detect and correct movement between pieces. NIBIB-funded researchers are also building motion correction systems that could reduce repeat exams and anesthesia use.
These tools help, but they do not replace a still patient. Your cooperation remains the biggest factor you control.
The bottom line
Moving during an MRI does not hurt you, but it blurs or ghosts the images. Usually the technologist repeats one series and you leave a few minutes later. Breathing, swallowing, and small head shifts are the usual causes, and children and hospital patients are affected most. Get comfortable first, follow breath-hold cues, and speak up instead of shifting.
Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your radiology team about any concern you have with lying still for your scan.