Understanding the Factors That Affect Image Quality in MRI Machines
Updated: 4 days ago
Several things affect how clear an MRI image is. Some come from the machine, like magnet strength, the coils, and the scan settings. Others come from the patient, like movement, body size, and metal in or on the body. This guide explains each factor in plain language and what you can do to help your scan come out as clear as possible.
Why MRI image quality matters
An MRI uses a strong magnet, radio waves, and a computer to make detailed pictures of the inside of the body. It is especially good at showing soft tissues such as the brain, spinal cord, muscles, ligaments, and organs. If you want a quick refresher on the basics, see our guide on how an MRI works.
Clear images help the radiologist see small details. Blurry or noisy images can hide those details or make something look different than it really is. That is why the MRI team works hard to get the sharpest pictures they can, and why your part, like staying still, matters too.
Technical factors
These factors come from the scanner and how the scan is set up.
Magnetic field strength
Magnet strength is measured in units called Tesla (T). In general, a stronger magnet produces more signal. More signal compared with background "noise" can mean sharper, more detailed images.
Stronger is not the only thing that counts, though. The coils, the software, the scan settings, and the skill of the technologist all play a big part. Many scans that answer a doctor's question well are done on a range of field strengths. To learn more, read how magnetic strength affects the imaging process.
Radiofrequency (RF) coils
Coils are the parts that send and pick up the radio signals used to build the image. Different coils are made for different body parts, such as the head, knee, shoulder, or spine.
The coil is often placed close to or around the area being scanned. The closer and better fitted the coil is, the stronger the signal it picks up. That is why the technologist may place a lightweight frame or pad over your knee or around your head. It does not hurt. It just helps the pictures come out clearer.
Gradient coils
Gradient coils are built into the scanner. They slightly change the magnetic field across the body so the computer can tell exactly where each signal came from. They are also what make the loud knocking and tapping sounds during a scan.
When gradient coils work well, images are sharp and correctly shaped. Problems with them can cause distortions or artifacts, which are unwanted marks or patterns on the image.
Scan settings
Every MRI is made up of several short sets of pictures, called sequences. Each sequence uses its own settings. Two common ones you may see named are:
Repetition time (TR): how often the radio pulses are repeated
Echo time (TE): how long the scanner waits before collecting the signal
Changing these settings changes how different tissues look. For example, some sequences make fluid look bright, and others make fat look bright. The technologist picks settings based on the body part and the question your doctor is asking. There is often a trade-off between detail, scan time, and how much noise is in the image.
Patient-related factors
You also have an effect on image quality. Some of these factors you can control, and some you can't.
Movement
Movement is one of the most common causes of blurry MRI images. Even small motions, like shifting your leg or swallowing during a head scan, can smear the picture. Breathing and a beating heart can also cause motion in chest and belly scans, which is why you may be asked to hold your breath for short periods.
If an image is too blurry, the technologist may need to repeat that sequence. Learn more in what happens if you move during an MRI.
Body size and shape
Body size and shape can affect how well the coils pick up signal. It can also affect how the body fits in the scanner. The team adjusts positioning, padding, and coils to get the best images possible for each person.
Metal and medical devices
Metal can distort the magnetic field near it. This can create dark spots or warped areas on the image. Sources of metal include:
Surgical clips, plates, screws, or joint replacements
Dental work, such as braces
Some tattoo inks and permanent makeup
Clothing with zippers, snaps, or metallic thread
Some makeup, lotions, or deodorants with metal particles
Some medical devices, such as pacemakers or cochlear implants, raise safety questions as well as image quality concerns. Always tell your doctor and the MRI team about any implant or device before your scan. They will check whether it is safe to scan and whether anything needs to be done first.
Anxiety and claustrophobia
Feeling nervous or closed in can make it hard to lie still. That can lead to blurry images. If you feel anxious about MRIs, tell your doctor and the MRI team ahead of time. Our tips on how to overcome claustrophobia during an MRI may help.
How radiologists check image quality
Radiologists are doctors trained to read medical images. When they review your MRI, they look at things like:
Signal-to-noise ratio: how strong the useful signal is compared with background grain
Contrast: how clearly different tissues stand apart from each other
Resolution: how small a detail the image can show
They also watch for artifacts. Knowing what an artifact looks like helps the radiologist avoid mistaking it for a real problem.
Common MRI artifacts
An artifact is something that shows up on the image but is not really part of your body. Common types include:
Motion artifacts: blurring or "ghost" copies caused by movement, breathing, or blood flow
Susceptibility artifacts: dark or warped areas near metal, or where air and tissue meet
Chemical shift artifacts: thin bright or dark lines where fat and water-based tissue meet
Technologists and radiologists know how to reduce many of these. They may change the scan settings, adjust your position, or repeat a sequence.
How image quality is improved
Getting a clear MRI is a team effort. Here is how the imaging team helps:
Choosing the right coil and placing it close to the area being scanned
Picking scan settings that fit the body part and the medical question
Using padding and supports to help you stay comfortable and still
Using modern image reconstruction software that can reduce noise and shorten some scans
Repeating a sequence if it comes out blurry
And here is how you can help:
Remove all metal, jewelry, and hair accessories before the scan
Tell the team about any implants, devices, or past surgeries
Get comfortable before the scan starts, and speak up if something hurts
Stay as still as you can during each set of pictures
Follow breathing instructions if you are given them
How image quality affects your care
Clear images give the radiologist the best chance to see what is going on. This helps your doctor understand your condition and plan next steps. Good image quality matters for many types of scans, including brain, spine, joint, and organ imaging.
After your scan, the radiologist writes a report for your doctor. If you want help understanding it, our guide to reading your radiology report walks through common terms.
Frequently asked questions
What is the most common cause of a blurry MRI?
Movement is one of the most common causes. Even small movements during a sequence can blur the image. Staying as still as you can is one of the best ways to help.
Does a stronger magnet always mean a better MRI?
Not always. A stronger magnet can give more signal, but coils, scan settings, software, and the skill of the team also matter a lot. Your doctor and the imaging center choose the right exam for your needs.
Can metal in my body ruin an MRI?
Metal can cause dark or warped spots near where it sits, which can make that area harder to see. Some implants are also a safety concern. Always tell the MRI team about any metal or devices before your scan.
Why did the technologist repeat part of my scan?
A sequence may be repeated if it came out blurry or if the team needs a slightly different view. This is a normal part of getting good images and does not mean something is wrong.
Can I wear makeup or deodorant during an MRI?
Some products contain metal particles that can affect images. It is best to skip them or ask the team first. See can you wear deodorant during an MRI for more.
Related reading
Schedule an MRI at Millenium MRI
Millenium MRI has centers in Ocala, Largo, and Tamarac, Florida, and in North Little Rock, Springdale, Jonesboro, and Marion, Arkansas. Our scans are read by board-certified radiologists and performed by ARRT-certified technologists. Results are usually sent to your doctor within 24 hours, and same-day appointments are often available. We accept most insurance plans, workers' compensation, personal injury cases, and self-pay. Call your nearest center or request an appointment online.
This article is for general information and is not medical advice. Talk with your doctor about your specific situation.
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