Portable low-field scanners could revolutionize medical imaging in nations rich and poor—if doctors embrace them. LongReads
The patient, a man in his 70s with a shock of silver hair, lies in the neuro intensive care unit at Yale New Haven Hospital. Looking at him, you’d never know that a few days earlier a tumor was removed from his pituitary gland. The operation didn’t leave a mark because, as is standard, surgeons reached the tumor through his nose. He chats cheerfully with a pair of research associates who have come to check his progress with a new and potentially revolutionary device they are testing.
If you’re fortunate enough to be able to get one, that is. An MRI scanner employs a magnetic field to twirl atomic nuclei in living tissue—specifically the protons at the heart of hydrogen atoms—so that they emit radio waves. To generate the field, a standard scanner employs a large, powerful superconducting electromagnet that pushes a machine’s cost to $1.5 million or more, pricing MRI out of reach of 70% of the world’s population.
That fleeting monotone radio hum reveals little. To create an image, the scanner must distinguish among waves coming from different points in the body. To do this, it sculpts the magnetic field, which makes protons at different locations sing at different frequencies and states of synchrony. The scanner must also distinguish one type of tissue from another, which it does by exploiting the fact that the radio signals fade at different rates in different tissues.
A stronger field makes all this easier by polarizing the protons more thoroughly and creating a bigger signal. A standard scanner’s magnet produces a field of 1.5 tesla—30,000 times as strong as Earth’s field—and some reach 3 or 7 tesla. Even so, the protons pointing along a 1.5-tesla field outnumber those pointing the other way by just 0.001%. Reduce the field strength by a factor of 25 and the polarization falls with it. The signal-to-noise ratio plummets even more, by a factor of nearly 300.
Even so, gathering data fast enough for standard image reconstruction remains a challenge. One solution is to employ novel signal processing techniques, including artificial intelligence. Hyperfine engineers use a set of training images to teach a program called a neural network to construct brain images from relatively sparse data, says Khan Siddiqui, Hyperfine’s chief medical officer and chief strategy officer. “That’s where our secret sauce comes in.
The Swoop’s advantages have won it fans. “Oh, my God, what a beautiful, beautiful piece of technology,” says Steven Schiff, a pediatric neurosurgeon at Yale University who has no financial interest in Hyperfine. Still, the Swoop can miss details a high-field scanner would catch because its resolution of 1.5 millimeters is half that of a standard scanner. For example, Sheth’s team used it to image the brains of 50 patients who had had an ischemic stroke, visible with standard MRI.
Johnes Obungoloch and Andrew Webb with the magnet for a scanner that will guide surgeries at a pediatric hospital in Uganda.
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