Biomedical engineering enters the quantum realm

Joseph Flaig

The sensors measure the magnetic field generated by human brain activity, and observers can infer what a brain is doing
The sensors measure the magnetic field generated by human brain activity, and observers can infer what a brain is doing

Biomedical devices are the most advanced technology that some of us are likely to come into contact with, and often have the intimidating size to match.

MRI scanners fill entire rooms, for example, with space for patients inside and cooling for the giant magnets. 

Increasingly, however, biomedical devices are becoming smaller because of miniaturisation. Tiny sensors, such as those developed by RVmagnetics, are shrinking thanks to incredibly thin ‘microwires’ that react to physical qualities such as heat. 

Keen to increase patient comfort and enable new monitoring capabilities, researchers are also applying miniaturisation to much larger devices. One striking example is a brain scanner developed by a team at the University of Nottingham, University of Oxford and University College London, which condenses a half-tonne scanner into something much lighter and smaller. The magnetoencephalography (Meg) device, which measures brain activity, now fits into a bike-helmet-sized package. It could be used to measure brain activity in young children, allowing the study of conditions such as epilepsy and autism. 

Optical pumping

The huge change in size was enabled by quantum sensors developed by Quspin in Colorado. Like MRI scanners, conventional Meg systems use sensors that need cooling with liquid helium, requiring significant infrastructure. Traditional scanners are also in a fixed position, stopping patient movement. 

Instead, the quantum sensors exploit the properties of alkaline rubidium atoms. Circularly-polarised light is shined on the atoms in a process known as optical pumping, which puts them all in the same quantum state and gives them the same magnetic moment – they all point in the same direction. As the gas of atoms is magnetic, it no longer absorbs laser light. If the atoms experience a magnetic field, the alignment of the magnetic moment changes and they start absorbing light again. Each sensor has a laser, which monitors the amount of light passing through the gas. 

In this way – and thanks to some clever ‘noise cancelling’ tricks to remove the Earth’s background field – the sensors measure the magnetic field generated by human brain activity, and observers can infer what a brain is doing. 

Allowing patients, particularly children, to move during scans enables study and solutions to complex problems, says research leader Professor Matthew Brookes from Nottingham. “Imagine being able to work out the switch that flicks in a child that allows them to start walking or talking,” he says. “That is what we are trying to find out.”

Further applications

The miniaturisation enabled by quantum sensors could also unlock the study of many other conditions. While conventional scanners are large and fixed, quantum sensors can be adapted to study different systems and parts of the body. 

“There are a lot of other things in the body that use electrical current – your muscles, your heart, your gut, your spine,” says Brookes. “In pregnant women the unborn baby generates a magnetic field… what the miniaturisation allows you to do is say ‘I want to take my brain imaging system, but actually I want to measure the magnetic field from the foetal heart, so I’m going to take my sensors and put them around a mum-to-be’s abdomen’.”

Smaller sensors could be arranged to fit around a pregnancy ‘bump,’ says Brookes, or aligned in a ‘plank’ to scan a spine. He predicts many more applications enabled by the quantum sensors.

“In the last four or five years, we have effectively gone from a half-tonne machine to a Lego-style helmet, and the applications are beginning to catch up. We are just starting to scratch the surface of what we could do with this technology.”

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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers. 


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