An open MRI machine replaces the long, narrow tunnel of a conventional scanner with a wide gap between two flat magnetic surfaces, leaving most or all of the patient’s body exposed to the surrounding room. The most common design looks like a large letter “C” or like two oversized dinner plates separated by a thick pillar, with the patient lying on a table that slides into the space between them. Some models go further, standing the patient upright inside what resembles a walk-in booth with no top or front wall. The visual difference from a traditional closed-bore MRI is striking and immediate, but the design choices behind that openness involve real engineering tradeoffs that affect image quality, noise, and what the scanner can actually do.
The Basic Shape Compared to a Closed-Bore Scanner
A conventional MRI looks like a large horizontal cylinder, roughly two feet in diameter on the inside, that the patient slides into on a motorized table. The bore is usually about 60 centimeters wide, and the tube can extend over six feet long. This tunnel shape works well for generating a strong, uniform magnetic field, but it means the patient is almost completely enclosed during the scan.
An open MRI scraps that cylinder. Instead of wrapping a magnet all the way around the patient, the machine uses two flat magnet assemblies positioned above and below (or, in some designs, to the left and right of) the patient, connected at the back or side by a structural support. The result is a scanning space that is open on at least two and sometimes three sides. You can see out, someone standing nearby can reach in and hold your hand, and the sense of confinement drops dramatically. The magnets in these systems typically produce a vertical field running straight up and down through the patient, rather than the horizontal field running head-to-toe that a closed bore generates.
Common Configurations
Not all open MRI machines look the same. The field has settled into a few recognizable shapes, each with a slightly different balance of openness and performance.
- C-arm design: Two horizontal magnet poles sit above and below the patient, connected on one side by a thick C-shaped support. Three sides remain completely open. This is the most widely recognized open MRI layout and is common in outpatient imaging centers.
- Pillar-post (H-frame) design: Similar to the C-arm, but with two vertical pillars connecting the upper and lower magnet assemblies, one on each side. This creates an H-shaped profile when viewed from the front. The patient still has generous open space on the left and right, but the pillars sit at the edges of their peripheral vision.
- Wide-bore closed design: Technically still a tunnel, but with a bore diameter of 70 centimeters or more, sometimes marketed as “open” or “semi-open.” It looks like a shorter, fatter version of a standard closed scanner. It offers more room inside but does not eliminate the tunnel entirely, so calling it truly open is a stretch.
- Upright (stand-up) design: The patient stands or sits between two vertical magnet assemblies that face each other like a pair of tall walls, with no top enclosure. One system described in the literature operates at 0.6 Tesla with a horizontal magnetic field and includes a motorized table that can tilt the patient from lying flat to standing fully upright.
The upright configuration is the most visually unusual. The scanner itself looks more like a piece of gym equipment than traditional medical imaging hardware. Its top-and-front-open construction leaves the patient’s head and upper body entirely uncovered, and the motorized table allows both recumbent and weight-bearing positions without moving the patient to a different machine.1Rivista di Neuroradiologia. Upright, Weight-Bearing, Dynamic-Kinetic MRI of the Spine
What Patients Actually Experience Inside One
The practical difference between lying inside a closed bore and resting between the open plates is hard to overstate for anyone who struggles with tight spaces. In a closed scanner, the tube wall is typically inches from your face. In most open designs, the nearest surface is the magnet plate above you, and even that is a comfortable distance away while the sides remain completely clear.
Research backs up what you would expect from that difference. A comparative study found that patients scanned in an open upright MRI reported claustrophobia at a rate of about 18%, compared to roughly 58% in a conventional closed system. Premature scan terminations dropped from 31% in the closed scanner to about 5% in the open one, and the use of sedatives fell from nearly 47% to around 5%.2Radiography. Patient-centric comparative analysis of experiences in open upright and conventional closed MRI scanners A separate study focused specifically on highly claustrophobic patients found that the scan termination rate plummeted from about 58% in closed magnets to roughly 8% in an open 1.0 Tesla system, and self-reported anxiety scores on a 0-to-100 scale dropped from an average near 87 to around 30.3PubMed. MR imaging of claustrophobic patients in an open 1.0T scanner: motion artifacts and patient acceptability compared with closed bore magnets
Those numbers matter beyond patient comfort. Every scan that has to be stopped partway through wastes time, delays diagnosis, and sometimes means the patient needs to be rescheduled under sedation or general anesthesia. For children, avoiding sedation is an especially valuable benefit, since the open layout and reduced sense of confinement can make the difference between a cooperative child and one who needs to be put under.
Why They Use Weaker Magnets and What That Means for Images
Most open MRI systems operate at field strengths between 0.2 and 1.0 Tesla, while mainstream closed-bore scanners typically run at 1.5 or 3.0 Tesla. The reason is physics and geometry: creating a powerful, uniform magnetic field is easier inside a closed cylinder than across an open gap. Keeping that gap open for patient access means spreading the magnetic field across a wider space, which is harder to do at high intensity.
Lower field strength translates directly to a weaker signal coming back from the patient’s tissues, and a weaker signal means grainier images unless you compensate by scanning longer. For many routine clinical tasks, the image quality from a well-tuned open system at 0.5 or 1.0 Tesla is perfectly adequate. Musculoskeletal exams, basic brain scans, and spine imaging all work. But for applications that demand the sharpest possible detail, like cardiac imaging, functional brain mapping, or catching very small lesions, higher-field closed systems still have a clear edge.
Engineers have worked to close this gap. Gradient coil design, which controls how the machine encodes spatial information, has been a major area of innovation. One approach uses coils shaped to fit the open geometry’s flat-plate magnets, optimizing power efficiency and field uniformity specifically for biplanar configurations.4PubMed. 3D gradient coil design for open MRI systems Another strategy involves shaping gradient coils on convex rather than flat surfaces to squeeze stronger gradient fields out of a vertical-field open design while preserving patient access space.5Measurement Science and Technology. Design of convex-surface gradient coils for a vertical-field open MRI system The broader trend in superconducting magnet research has been to push for non-traditional geometries that prioritize openness and patient comfort without sacrificing field performance entirely.6PubMed Central. Novel technologies and configurations of superconducting magnets for MRI
One Upside You Might Not Expect: Less Noise
MRI machines are notoriously loud. The banging and buzzing come from rapid electrical pulses running through the gradient coils, which vibrate against the magnetic field the same way a speaker cone does. In a closed-bore scanner, you are sitting inside a resonant tube that amplifies those vibrations, and at high field strengths the acoustic output can be genuinely punishing.
A survey of 15 MRI scanners ranging from 0.2 to 3.0 Tesla found that noise levels varied enormously by field strength: a 0.23 Tesla system measured around 82.5 decibels, while a 3.0 Tesla system hit about 118 decibels.7Wiley Online Library. Investigation of acoustic noise on 15 MRI scanners from 0.2 T to 3 T For context, 85 decibels is roughly the level of heavy city traffic and is the threshold at which prolonged exposure starts to risk hearing damage. A 118-decibel reading is closer to a rock concert or a chainsaw. Open MRI systems, which tend to operate at lower field strengths and lack the echo-chamber effect of a closed bore, are generally much quieter. Patients who have experienced both often comment on the difference unprompted.
Scanning While Standing, Bending, and Moving
One of the most interesting things an open MRI can do that a tunnel scanner simply cannot is image the body under load and in motion. When you lie flat inside a closed bore, your spine, knees, and hips are not bearing any weight. Disc herniations, ligament laxity, and joint instability can look different or even disappear in that unloaded position. An upright open MRI lets clinicians see what is actually happening when gravity is pulling on your skeleton.
The upright system described earlier allows flexion and extension movements of the spine during scanning, which can reveal disc bulges and nerve compressions that are invisible in a standard recumbent scan.1Rivista di Neuroradiologia. Upright, Weight-Bearing, Dynamic-Kinetic MRI of the Spine Researchers have also used open MRI to study knee joint motion in real time, measuring patellar tracking and rotation with accuracy within about 2 millimeters at speeds up to 38 millimeters per second in a 0.5 Tesla open-bore system.8PubMed Central. Feasibility of using real-time MRI to measure joint kinematics in 1.5T and open-bore 0.5T systems
Dynamic imaging of ligaments is another area where open designs shine. A study using a 1.0 Tesla open MRI scanned the anterior cruciate ligament at multiple positions of knee flexion and found that the ligament lengthened significantly as the knee bent from hyperextension to 90 degrees, going from roughly 32 millimeters to about 36 millimeters. The angles at which the ligament attached to bone also changed substantially across positions.9PubMed. A dynamic study of the anterior cruciate ligament of the knee using an open MRI That kind of in-vivo dynamic measurement is essentially impossible in a conventional closed bore, where the patient must stay perfectly still in one fixed position.
Open MRI in the Operating Room
The same open-sided geometry that helps anxious patients also helps surgeons. In a closed bore, there is no way to reach the patient during a scan. The tube is in the way. Open designs were recognized early on as a potential game-changer for MRI-guided procedures because they allow direct physical access to the patient while imaging is in progress.
Low-field open scanners, usually around 0.2 Tesla, entered clinical use for interventional and intraoperative work in the early 1990s. The open configuration enabled physicians to perform biopsies, drain cysts, and guide thermal ablations under real-time MRI visualization for the first time.10PubMed. Interventional and intraoperative MRI at low field scanner–a review More recently, researchers have demonstrated MRI-guided laparoscopic surgery in an open MRI operating theater, using a real-time augmented reality navigation system that overlays MRI data onto the surgical field. Standard MRI-incompatible surgical instruments could be used in the area outside the scanner’s strongest magnetic zone, and the patient could be moved in and out of the imaging gap quickly for updated scans during the procedure.11PubMed. Image-guided laparoscopic surgery in an open MRI operating theater
The tradeoff in the surgical setting is the same one that applies everywhere else: lower field strength means less image detail. But for guiding the tip of a needle or confirming that a tumor margin has been fully resected, the resolution from a low-field open system is often enough. The ability to image mid-procedure without moving the patient to a different room easily justifies the quality compromise.
Metal Implants and Low-Field Advantages
One area where lower-field open MRI systems can actually outperform their high-field counterparts is imaging near metallic hardware. Joint replacements, spinal fusion rods, and dental implants all create artifacts in MRI, distortions and signal voids caused by the metal warping the magnetic field in its immediate vicinity. These artifacts get worse as field strength goes up, because the metal’s effect on the field is amplified proportionally. Research comparing metal artifact severity between a 0.55 Tesla system and a 1.5 Tesla system in patients with spinal implants found that the lower-field scanner produced less artifact and better visualization of anatomy near the hardware.12PubMed. Comparing Metal Artifact Severity and Ability to Assess Near-Metal Anatomy Between 0.55 T and 1.5 T MRI in Patients with Metallic Spinal Implants-A Scanner Comparison Study
This means that for patients who need follow-up imaging after a spinal fusion or knee replacement, a lower-field open scanner may actually be the better tool for the job, not just a more comfortable alternative but a diagnostically superior one in that specific context.
Portable and Bedside Systems
The latest evolution of open MRI design does not look like a scanner room at all. Portable low-field MRI systems operating at field strengths as low as 0.064 Tesla are small enough to be wheeled on a cart to a patient’s bedside, an ICU, or even a remote clinic. They look more like a piece of luggage on wheels with a head-sized opening than anything resembling traditional imaging equipment.
These systems have shown real clinical promise. A study using a portable 0.064 Tesla unit to image confirmed stroke patients at the bedside detected the infarct in 90% of cases across cortical, subcortical, and cerebellar brain regions.13PubMed Central. Portable, low-field magnetic resonance imaging enables highly accessible and dynamic bedside evaluation of ischemic stroke The images are not as detailed as what you would get from a 1.5 or 3.0 Tesla machine, but for a stroke patient who cannot be safely transported down the hall to a radiology suite, having any MRI at the bedside is a leap forward from having none.
The broader appeal of portable systems lies in their dramatically lower cost and infrastructure requirements. They do not need a specially shielded room, a dedicated power supply, or a liquid helium cooling system. Their portability and reduced operational demands make them valuable in point-of-care settings, remote locations, and during surgical procedures where moving the patient is impractical.14PubMed Central. Low-field and portable MRI technology: advancements and innovations In terms of appearance, these bedside units look nothing like either a conventional closed scanner or a traditional open MRI. They are the smallest, most visually unassuming members of the MRI family, and they represent the logical endpoint of the design philosophy that open MRI started: bring the imaging to the patient, not the patient to the imaging.
Who Should Actually Choose an Open MRI
Open MRI is not the right scanner for every situation, but there are clear cases where it is the better or even the only viable option. Patients with severe claustrophobia who would otherwise require sedation or refuse the scan entirely are the most obvious candidates. Patients whose body size exceeds the bore diameter of a closed scanner are another, since many open designs accommodate a much wider range of body types.
Children who can stay still with some coaching but would need anesthesia in a claustrophobic environment benefit from the open layout. Patients with metal implants who need imaging near the hardware may get more useful diagnostic results from a lower-field system. And anyone whose clinical question specifically involves how a joint or spine behaves under load or during movement needs a scanner that allows those positions, which means an open or upright design.
If your doctor has ordered an MRI for a condition where image quality at the highest field strength is critical, like staging a small tumor, mapping brain function before neurosurgery, or detailed cardiac imaging, a 1.5 or 3.0 Tesla closed-bore system is still the standard choice. The decision is not about which machine is better in the abstract. It is about which machine best answers the clinical question while keeping the patient cooperative enough to complete the scan. A perfect-resolution image that never gets acquired because the patient panics and leaves is worth less than a slightly grainier image that actually exists.