image source, Besides
- author, Chris Baranyuk
- Author Name, BBC, technology
Reading time: 6 min
Lying on your back inside a large hospital scanner as far as possible with your arms above your head for 45 minutes is not the most fun..
That’s what patients at London’s Royal Brompton Hospital had to do for certain lung scans until the hospital installed a new device last year that cut those scans down to just 15 minutes.
This is partly due to the scanner’s image processing technology, but also due to a special material known as CZT (Cadmium Zinc Telluride), which allows the machine to create highly detailed 3D images of patients’ lungs.
“You get wonderful images with this scanner,” says Dr. Kshama Vehalekar, head of nuclear medicine and PET (positron emission tomography).
“It’s a real feat of engineering and physics.”
The CZT on the machine installed at the hospital in August was made by Kromek, a British company and one of the few in the world that can do it.
You may never have heard of it, but in Vehalekar’s words, it’s “revolutionizing” medical imaging.
The remarkable material also has many other uses, such as in X-ray telescopes, radiation detectors and airport security scanners.
And it is increasingly in demand.
image source, Guy’s and St Thomas’ NHS Foundation Trust
Studies of lung patients by Dr. Vehalekar and her colleagues include looking for multiple tiny blood clots in people with long-term Covid or, for example, a larger blood clot known as a pulmonary embolism.
The £1 million (about $1.4 million) scanner works by detecting gamma rays emitted by a radioactive substance injected into patients’ bodies.
But the sensitivity of the scanner means that less of this substance is required than before.
“We can reduce the doses by about 30%,” says the doctor.
High demand, low supply
While CZT-based scanners in general are not new, large whole-body scanners like this one are a relatively recent innovation.
CZT has been around for decades, but is notoriously difficult to manufacture.
“It took a long time to turn it into an industrial-scale manufacturing process,” says Arnab Basu, founding CEO of Kromek.
The company’s facility in Sedgefield, England, has 170 small ovens in a facility that Dr. Basu describes as “like a server farm.”
In these furnaces, a special powder is heated, melted, and then solidified, forming a monocrystalline structure.
The whole process takes weeks.
“Atom by atom, the crystals are rearranged (…) until they are completely aligned,” Basu explains.
A newly created CZT semiconductor can detect tiny photonic particles in X-rays and gamma rays with incredible precision, like a highly specialized version of the photosensitive silicon image sensor found in your smartphone’s camera.
Whenever a high-energy photon hits the CZT, it mobilizes an electron, and this electrical signal can be used to create an image. Previous scanning technology used a two-step process that was not as accurate.
“It’s digital,” says Basu.
“This is a single conversion step. It stores all the important information, such as the time and energy of the X-rays hitting the CZT detector; color or spectroscopic images can be produced.”
He adds that CZT-based scanners are currently used to detect explosives at UK airports and to scan checked baggage at some US airports.
“We expect CZT to enter the carry-on segment in the coming years.”
Selected material
But it is not always easy to get CZT.
Henryk Krawczynski of Washington University in St Louis, US, has previously used the material in space telescopes tethered to high-altitude balloons.
These detectors can pick up X-rays from both neutron stars and the plasma around black holes.
image source, Besides
Professor Krawczynski needs very thin pieces of CZT, 0.8mm, for his telescopes as this helps reduce the amount of background radiation they pick up, allowing for a sharper signal.
“We would like to purchase 17 new detectors,” he says. “They are very difficult to lose weight.”
Kromek could not help him because, according to Basu, his company is now in high demand.
“We support many research organizations,” he adds. “It’s very difficult for us to do a hundred different things. Each research project requires a special type of detector structure.”
It’s not a crisis for Krawczynski: He says he may use CZT, which he has from previous research, or cadmium telluride, an alternative, for his next mission.
However, at the moment there are more serious problems.
The next mission was supposed to leave Antarctica in December, but “all the dates are changing,” Krawczynski says, because of the U.S. government shutdown in November.
Many other scientists use CZT.
In the UK, the Diamond Light Source research center in Oxfordshire has undergone a major upgrade that will improve its capabilities with the installation of CZT-based detectors.
The diamond light source is a synchrotron that blasts electrons around the giant ring at close to the speed of light. The magnets cause these electrons to lose energy as X-rays as they whiz by, and they are directed out of the ring into lines of light, for example for materials analysis.
Some recent experiments have involved analyzing impurities in aluminum during its smelting. A better understanding of these impurities can help improve recycled forms of the metal.
With the Diamond Light Source upgrade, scheduled for completion in 2030, the X-rays will become much brighter, meaning that existing sensors will not be able to detect them properly.
“It doesn’t make sense to spend all this money upgrading these facilities if you can’t detect the light they produce,” says Matt Weil, head of the detector development group at the Science and Technology Council, a stakeholder in the Diamond Light Source.
Thus, CZT is the material of choice here as well.
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