Open vs Closed MRI: What Is Actually Different

"Closed" MRI is the standard scanner: a tunnel, usually around 60 centimetres across, with the magnet wrapped around it. "Open" MRI covers several quite different designs that leave more of you outside the machine. The differences matter because they affect three things at once: how enclosed you feel, how strong the magnet is, and therefore how fine the pictures are. This guide sets out the four main scanner types available in the UK, what each is good and bad at, and the questions to ask a clinic before you pay for one in particular.

This page is general information, not medical advice. If you have symptoms that worry you, speak to your GP.

The four scanner types you will meet

• Standard tunnel (closed) scanner. A cylinder about 60 cm across, typically running at 1.5 tesla or 3 tesla. The workhorse of UK hospitals and most private clinics, and the reference against which everything else is judged.
• Wide-bore scanner. The same tunnel design with a 70 cm opening and often a shorter magnet, so your head is nearer the end and there is more room around your shoulders. Runs at the same field strengths as a standard tunnel.
• Open scanner. Two flat magnet plates above and below the table with open sides, so you can see out and someone can sit beside you. Most open systems run at a lower field strength than tunnel scanners.
• Upright or positional scanner. An open design in which you sit or stand, so the spine or a joint can be imaged under the load of your own body weight. Also lower field strength than a tunnel scanner.

Tesla is the unit of magnetic field strength. All else being equal, a stronger field gives more signal, which the scanner can spend on finer detail, a faster scan, or both. That is the trade at the heart of this whole question.

What field strength does to the pictures

An open scanner can produce diagnostic images for many common questions: a knee, a lumbar spine, a shoulder. For some questions it is the weaker tool. Small structures, subtle early changes, some brain and pelvic work and anything that benefits from thin slices are usually better served by a 1.5 T or 3 T tunnel scanner. Radiologists are candid about this, and a reputable open-scanner clinic will tell you when your question would be better answered elsewhere.

This is why the first thing to establish is not "open or closed" but "what is the scan for". A person with a torn meniscus and severe claustrophobia may be well served by an open scanner. A person being investigated for multiple sclerosis or a small pituitary lesion generally is not, and should be helped into a standard or wide-bore scanner instead, with the support described below.

The wide-bore scanner: the option most people have not heard of

If your difficulty is the enclosure rather than needing to be upright, a wide-bore scanner is usually the better compromise than a true open system. You keep full-strength imaging; you gain 10 cm of width, a shorter tunnel and, in many designs, your head outside the magnet for scans of the lower body. Many UK hospitals and private centres now have one, and clinics do not always advertise it, so it is worth asking specifically. Our guide to MRI options if you are claustrophobic goes through what else helps inside a standard scanner, from positioning feet-first to a companion in the room, and the NHS notes that you can ask about medicine to help you relax if anxiety is the barrier.

When an upright scanner is the right call

Upright scanners are designed for a specific purpose: imaging the spine, and sometimes a joint, while it is bearing weight. Some problems, including certain disc and spinal canal findings, are more apparent sitting or standing than lying flat. If a specialist has asked for a weight-bearing or positional MRI, an upright scanner is the only way to get it. If nobody has asked for one, its main benefit is comfort, and the lower field strength is a real cost. Treat it as a specialist tool, not a general-purpose alternative.

Larger patients and children

Weight and girth limits vary by machine. Standard tunnels typically have table limits and a bore that larger patients find tight or impossible; wide-bore and open systems were partly designed for exactly this, and some clinics quote limits well above a standard scanner. Ask for the table limit and bore diameter in writing before travelling. For children, the main issue is lying still for the scan, and an open scanner with a parent alongside can make the difference between a diagnostic study and an abandoned one. Our guide to private scans for children covers the practicalities.

Safety is the same whichever design you choose

Every MRI scanner, open or closed, is a powerful magnet, and the same rules apply: implants and devices must be checked against the manufacturer conditions, loose metal stays out of the room, and the safety questionnaire is not optional. The MHRA safety guidelines that UK units follow do not relax for open systems. If you have a pacemaker, a neurostimulator, cochlear implant or any other device, read our piece on MRI safety and metal implants and raise it with the clinic before booking.

Questions to ask the clinic

• What is the scanner type and field strength, in tesla?
• Is this scan appropriate for my question at that field strength, or would a tunnel scanner be better?
• What are the bore diameter and the table weight limit?
• Can someone come into the room with me?
• Will the report be written by a clinician appropriately qualified for this type of imaging, and is it included in the price?

A clinic that answers those five questions plainly is one you can trust with the scan. Our article on what to expect at an MRI scan covers the appointment itself.

Common questions

Is an open MRI as good as a closed MRI?

For many routine questions, yes. For fine detail, small structures and some neurological and pelvic work, a standard or wide-bore tunnel scanner at 1.5 T or 3 T is usually better, because open systems generally run at a lower field strength.

What is the difference between open and wide-bore MRI?

A wide-bore scanner is still a tunnel, but 70 cm across instead of about 60 cm, often shorter, and at full field strength. An open scanner has open sides between two magnet plates and usually a lower field strength.

Does an open MRI take longer?

Often, yes. With less signal from a weaker magnet, the scanner may need longer to collect enough data for a clear image.

Can I have an open MRI if I have an implant?

The same safety rules apply to every MRI scanner. The clinic must check your implant against its manufacturer conditions whichever design you use.