Portable MRI Scans Patients for Signs of Stroke - IEEE Spectrum

Mar 12, 2025

According to the World Health Organization, strokes are the second most common cause of death worldwide. Of the 15 million patients annually, one-third die and another third are left with permanent disabilities. A new design for a portable MRI scanner has the potential to make a major impact on those numbers.

Medical imaging is essential in diagnosing a stroke. Strokes have two major causes, and the difference is critical. Ischemic strokes are caused by a blockage of blood vessels in the brain, and account for about nine out of 10 cases. Hemorrhagic strokes are the result of bleeding in the brain. Choosing the wrong treatment can be damaging, or even fatal.

A better imaging device could result in faster diagnoses. Many medical facilities—even in developed nations—lack MRI scanners and other sophisticated imaging equipment. This can delay a diagnosis past the “golden hour”—the first hour of a stroke, when treatment can be most effective. Delay increases the chance of brain-tissue damage due to oxygen deprivation.

Even if an MRI machine is available, patients must be transported from a facility’s emergency department to the radiology department for imaging and then returned for treatment. Scientists at Wellumio in Wellington, New Zealand, came up with the idea that a mobile unit that could scan just the patient’s head in the emergency department would allow imaging to be done right there, while the patient is still on a gurney.

The result is Axana: an MRI scanner mounted on a mobile pedestal. Axana’s toroid (doughnut) shape is just large enough for the patient’s head. The device is controlled by a simple touchscreen interface, which means that it requires far less training than traditional imaging systems.

While Axana uses the same sensors as standard MRI machines, the signals are provided in a very different manner. Traditional MRI relies on three pulsed gradient electromagnetic coils along x, y, and z axes. (This is what makes an MRI scan feel like being in a steel drum while goblins pound on the outside with sledgehammers.) The result is highly detailed three-dimensional imaging of soft tissues.

Axana does not use pulsed gradient coils. Instead, it uses magnetic fields at different frequencies to align the hydrogen atoms in soft tissues. The machine creates these fields in different regions of the patient’s head using different frequencies to achieve the spatial resolution.

As it stands now, the images are very low resolution, but they’re sufficient for gross anatomy analysis. The company intends to increase the number of coils operating at more frequencies in the next version to increase the resolution. The system compares the rate of signal decay in the tissue with the diffusion of blood in the tissues. This can provide enough information to detect the impaired blood diffusion that would indicate an ischemic stroke. The data are displayed in an image that is color coded to draw attention to areas of impaired diffusion.

Axana does not require any AI to process the data, just straightforward physics and mathematics. This makes the interpretation of the data much simpler and more reliable.

The end result is a portable device that can be produced at a relatively low cost compared with a traditional MRI installation, which can cost between US $1 to $3 million. The current prototype weighs in at about 100 kilograms, which makes it a bit large for ambulance applications but should fit well in most emergency department facilities. Its power consumption is low enough for the device to be powered by a standard wall outlet, and it contains a battery, so it can continue to operate when moved from one outlet to another.

“Further down the track, we definitely want the device to be capable of operation out in the field,” says Paul Teal, Wellumio’s chief data scientist. “For this application, perhaps three or four scans is all that would be required in a single deployment.”

At present, the prototype is undergoing preclinical testing with human patients at the Royal Melbourne Hospital, in Australia. The system is designed only to detect ischemic stroke at this point, though the company intends to expand its uses to include hemorrhagic diagnoses as well. Ultimately, it could be useful in detecting other forms of head trauma.

A major part of the company’s mission is to make this device available in rural and underserved communities through its small size, lower cost, and reduced need for training. “In order to really make a difference in the time to treatment for treatable ischemic stroke, the device must be operated by emergency room doctors (and eventually paramedics) without the oversight of a neurologist and/or radiologist,” says Teal. “There is a lot of regulatory approval that must be gained before the device can be used in this way, but it is actually quite feasible.”