What tesla strength is a typical open MRI?

Older open scanners often run at about 0.2 tesla, and newer open designs reach about 1.0 tesla. Standard closed scanners usually run at 1.5 or 3 tesla. Ask the imaging center for the exact number before you book.

Is a 3T MRI always better than a 1.5T MRI?

Not always. Higher field gives more signal and sharper detail, but a well-run 1.5 tesla exam is the standard for most body and joint imaging. The right choice depends on the body part and the question your doctor is asking.

Can my doctor ask for a repeat scan if the open MRI is unclear?

Yes. If a low-field image cannot answer the question, the radiologist may recommend a repeat on a higher-field scanner. That can mean a second bill, so ask up front whether your exam is a good fit for an open scanner.

Does insurance treat open and closed MRI differently?

Insurers usually cover the exam by body part and medical need, not by scanner type. Prior authorization rules still apply, and prices vary by facility. Check with your plan and the imaging center before scheduling.

Is low-field MRI better for people with metal implants?

It can help. Lower field strength causes less distortion around metal, so some images near implants can be clearer. Your radiologist will weigh that against the lower overall detail.

Is an Open MRI as Accurate as a Closed MRI?

The short answer: Often close, but not always. Many open MRI scanners run at a low magnetic field strength (older designs at about 0.2 tesla), which means less signal, grainier pictures, and longer scans than a closed 1.5 or 3 tesla machine. Studies show open and low-field scans catch most torn ligaments, big meniscus tears, and fractures about as well, but they miss more small cartilage defects, low-grade meniscus tears, and some brain findings.

Why does an open MRI make different pictures than a closed one?

The main difference is not the shape of the machine. It is the strength of the magnet, measured in tesla (T).

Most closed scanners in use today run at 1.5 T or 3 T. A 2024 review in Skeletal Radiology notes that these machines give better contrast, a higher signal-to-noise ratio (SNR), higher resolution, and shorter scan times than low-field magnets. Classic open scanners use permanent magnets in a C-shaped frame and run at low field (1 T or less).

Not every open scanner is weak. The CLAUSTRO trial protocol notes that earlier open systems ran at about 0.2 T, with poor image quality especially in the brain. It also describes newer open scanners at 1.0 T. So the magnet strength matters more than the label.

The same review states the trade plainly: at the same scan time, a weaker field generally gives lower SNR and lower image quality. A radiologist can win some of that back by scanning longer or using thicker slices. Longer scans raise the chance that you move, and thicker slices can hide small findings.

Low field has one real advantage. It shows less distortion around metal implants and at air-tissue boundaries. That can help in some patients with metal hardware.

What do studies say about open MRI accuracy?

The research is older than you might expect, and most of it compares low-field against high-field machines rather than "open" against "closed" by name. Here is what the head-to-head studies found.

Multi-region trial. A prospective study of 401 patients at four centers scanned each person on an open low-field unit and a high-field unit, then checked results against surgery or follow-up. Accuracy was not meaningfully different for the kidney, shoulder, and spine. For the brain, high field had a small but significant edge.
Knee, 0.2 T vs 1.5 T. In a surgically confirmed knee study, meniscus tear sensitivity was 83% at 1.5 T and 75% at 0.2 T, with 97% specificity for both. ACL tear detection matched. But the low-field scanner missed 5 of 6 full-thickness cartilage defects that the 1.5 T scanner found.
Modern 0.55 T vs 3 T. A 2024 study of 25 knee patients used a new low-field scanner with deep learning reconstruction. It agreed with 3 T on bone bruises, fractures, ligament and tendon tears, and high-grade meniscus and cartilage damage. Agreement dropped for low-grade meniscus lesions, and readers were less confident about cartilage and meniscus at 0.55 T.
Modern 0.55 T vs 1.5 T. A 2023 study in 20 volunteers found similar diagnostic reads for meniscus and cartilage, though two of three main image types were rated lower at 0.55 T.

The pattern is consistent. Low field finds the obvious problems. It is weaker on small, subtle ones.

Which MRI exams lose the most on a low-field open scanner?

Based on the studies above, the gap is largest where the answer depends on fine detail:

Cartilage. Small or partial-thickness cartilage defects in the knee were the most commonly missed finding at low field.
Subtle meniscus tears. Big tears show up well. Low-grade tears are harder to call.
Brain. The one region where the 401-patient trial found a significant advantage for high field.
Fat-suppressed images. The Skeletal Radiology review explains that fat and water signals sit closer together at low field. That made standard fat suppression hard on conventional low-field scanners, and the substitute methods often look worse.

For a knee injury, this matters. If your doctor wants to know whether you tore your ACL, a low-field scan will usually answer it. If the question is early cartilage wear before surgery, the higher-field scan is the safer choice. Our knee MRI guide covers what those scans look for.

Does an open MRI take longer?

Usually, yes. Because the signal is weaker, a low-field scanner needs more time to collect enough of it for a clear picture. The Skeletal Radiology authors report that with modern software, a diagnostic low-field musculoskeletal exam commonly takes 20 to 30 minutes.

Time matters for image quality in its own right. RadiologyInfo, run by the American College of Radiology and the Radiological Society of North America, notes that high-quality images depend on your ability to stay still. If you are anxious or in pain, image quality suffers. A longer exam gives more time for movement to blur the pictures.

When is an open MRI a fair trade?

An open scan makes sense when the alternative is no scan at all, or a scan ruined by motion. Common cases include:

You cannot finish a closed scan even with preparation or sedation.
Your body size or weight exceeds a closed scanner's limits. RadiologyInfo notes that a large person may not fit in some machines and that scanners have weight limits.
The clinical question is straightforward, such as a suspected ligament tear or disc herniation.
A child or adult needs a parent or helper close by.

Keep your expectations in check about anxiety, though. In the randomized CLAUSTRO trial, 174 claustrophobia-prone patients were assigned to an open or a short-bore closed scanner. Claustrophobic events happened in 26% of open scans and 39% of short-bore scans, a difference that was not statistically significant. A 2024 survey of 800 patients also found no significant difference in how claustrophobic patients perceived open versus closed machines. For coping strategies that do help, see our post on MRI and claustrophobia.

Is a wide-bore MRI a better middle option?

For many people, yes. A wide-bore scanner is still a tube, but the opening is larger than the conventional 60 cm bore described in a 2026 comparison of 3 T systems. Wide-bore machines can run at full high-field strength, so you keep high-field image quality.

The CLAUSTRO protocol cites a cohort of over 55,000 patients scanned on a short, wide-bore 1.5 T machine with 97% noise reduction. That design cut claustrophobic reactions by a factor of up to 3 compared with conventional closed scanners.

A newer category is the wide-bore mid-field scanner. A 2026 case series used a 0.55 T scanner with an 80 cm bore to get diagnostic heart images in five patients with a BMI of 40 or higher. Patients like these are often excluded from standard 1.5 T and 3 T machines.

When you book, ask the imaging center two questions: what is the magnet strength, and what is the bore size? "Open" and "wide" are marketing words. Tesla numbers are not. Price can differ too, so compare with our guide to MRI costs without insurance.

The bottom line

A low-field open MRI answers many common questions well, especially large tears, fractures, and disc problems. It is less reliable for small cartilage damage, subtle meniscus tears, and some brain findings. If comfort is the issue, a wide-bore 1.5 T or 3 T scanner often gives you more room without giving up image quality. If you are still working out whether your symptoms need imaging at all, symptom.md can help you prepare questions for your doctor. Ask your ordering doctor or radiologist which field strength suits your specific question before you book.

Last updated: September 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your doctor or radiologist about which MRI scanner is right for your exam.