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Nanometer-Scale Magnet Makes Tiny, Powerful MRI

Harvard researchers produced miniscule MRI capable of generating 3-D images composed of individual electron spins

2 min read
Infographic showing workings of a magnetic resonance imagining (MRI) device.
Illustration: Harvard University

The trend in making more powerful magnetic resonance imagining (MRI) devices has been to produce larger magnets. A European consortium, for example, is building what will be the most powerful MRI, capable of producing a field of 11.75 teslas using a superconducting magnet strong enough to lift a 60-metric-ton battle tank.

However, researchers at Harvard University have gone in the opposite direction and built a device with a magnet only 20 nanometers across, or approximately 1/300th the size of a red blood cell. Despite its small size, the researchers claim that the magnet can produce a magnetic field gradient 100 000 times larger than even the most powerful conventional systems.

The trick is that this nanoscale magnet can be brought within nanometers of the object being imaged to produce a spatial resolution down to the nanoscale. Most hospital MRI scanners can only reach a spatial resolution of 1 millimeter. With this capability, the Harvard researchers someday hope to produce detailed images of individual molecules.

“What we’ve done, essentially, is to take a conventional MRI and miniaturize it,” said Amir Yacoby, professor of physics in a press release. “Functionally, it operates in the same way, but in doing that, we’ve had to change some of the components, and that has enabled us to achieve far greater resolution than conventional systems.”

In research published in the journal Nature Nanotechnology (“Subnanometre resolution in three-dimensional magnetic resonance imaging of individual dark spins”), Yacoby and his colleagues used a combination of their nanoscale magnet with a bit of quantum computing.

First, the quantum computing part: The Harvard team milled lab-grown diamonds into super fine tips and embedded an impurity into each, called a nitrogen vacancy (NV). This impurity acted as a quantum bit, or qubit, which is the key to the operation of quantum computers.

When the tip is scanned over the surface of a diamond crystal, the qubit interacts with the electrons on the surface of the crystal. It is these interactions that serve as the basis for images of the electrons spins. While making a quantum bit magnetometer sensitive enough to detect the spin of individual electrons was groundbreaking work in its own right, the distance between the qubit sensor and the object being imaged limited the system's spatial resolution.

To overcome this limitation, Yacoby and his colleagues brought the nanoscale magnet close to both the qubit sensor and the sample being examined. With this combination, the team was able to detect distribution of spins surrounding the sensor so that they were able to image the three-dimensional landscape of electronic spins at the diamond surface and achieve a spatial resolution of  0.8 nm laterally and 1.5 nm vertically.

“This is really a game of bringing both the magnet very close to generate large gradients, and bringing the detector very close to get larger signals,” Yacoby said. “It’s that combination that gives us both the spatial resolution and the detectability.”

The researchers are looking to push the technique beyond the ability to image the individual spin of electrons in 3-D and make it capable of imaging components within a molecule, such as the nuclear spins of the atoms making up the molecule.

“This is by no means an easy task, since the nuclear spin generates a signal that is 1/1000th that of the electron spin … but that’s where we’re headed,” said Yacoby.

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Are You Ready for Workplace Brain Scanning?

Extracting and using brain data will make workers happier and more productive, backers say

11 min read
A photo collage showing a man wearing a eeg headset while looking at a computer screen.
Nadia Radic

Get ready: Neurotechnology is coming to the workplace. Neural sensors are now reliable and affordable enough to support commercial pilot projects that extract productivity-enhancing data from workers’ brains. These projects aren’t confined to specialized workplaces; they’re also happening in offices, factories, farms, and airports. The companies and people behind these neurotech devices are certain that they will improve our lives. But there are serious questions about whether work should be organized around certain functions of the brain, rather than the person as a whole.

To be clear, the kind of neurotech that’s currently available is nowhere close to reading minds. Sensors detect electrical activity across different areas of the brain, and the patterns in that activity can be broadly correlated with different feelings or physiological responses, such as stress, focus, or a reaction to external stimuli. These data can be exploited to make workers more efficient—and, proponents of the technology say, to make them happier. Two of the most interesting innovators in this field are the Israel-based startup InnerEye, which aims to give workers superhuman abilities, and Emotiv, a Silicon Valley neurotech company that’s bringing a brain-tracking wearable to office workers, including those working remotely.

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