A novel semiconductor material, cadmium zinc telluride (CZT), is playing an increasingly vital role in advancements across medical imaging, security, and scientific research. While relatively unknown outside specialist circles, CZT’s unique ability to detect X-rays and gamma rays with high precision is revolutionizing scan times and reducing radiation exposure for patients-as demonstrated by a recent installation at London’s Royal Brompton Hospital [[1]]. Though, manufacturing this “wonder material” remains a complex and limited process, creating challenges for rapidly growing demand.
Fuente de la imagen, Kromek
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- Autor, Chris Baraniuk
- Título del autor, BBC, Tecnología
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Tiempo de lectura: 6 min
Lying flat on your back inside a large hospital scanner, as still as possible with your arms above your head, for 45 minutes isn’t the most enjoyable experience.
That’s what patients at London’s Royal Brompton Hospital had to do during certain lung scans, until the hospital installed a new device last year that reduced those exams to just 15 minutes.
This improvement is partly due to the scanner’s image processing technology, but also to a special material known as CZT (cadmium zinc telluride), which allows the machine to produce highly detailed three-dimensional images of patients’ lungs. Advances in medical imaging are continually improving diagnostic accuracy and patient comfort.
“With this scanner, you get beautiful images,” says Dr. Kshama Wechalekar, head of nuclear medicine and PET (Positron Emission Tomography).
“It’s a real feat of engineering and physics.”
The CZT in the machine, installed in August, was manufactured by Kromek, a British company, and one of the few in the world capable of producing it.
You may never have heard of it, but – as Wechalekar puts it – it’s causing a “revolution” in medical imaging.
This remarkable material also has many other uses, including in X-ray telescopes, radiation detectors, and airport security scanners.
And it’s increasingly in demand.
Fuente de la imagen, Guy’s and St Thomas’ NHS Foundation Trust
Lung investigations performed by Dr. Wechalekar and her colleagues involve looking for the presence of many tiny blood clots in people with long Covid, or a larger clot known as a pulmonary embolism, for example.
The scanner, which cost £1 million (approximately $1.4 million USD), works by detecting gamma rays emitted by a radioactive substance injected into patients’ bodies.
But the scanner’s sensitivity means less of this substance is needed than before.
“We can reduce the doses by around 30%,” the doctor says.
High Demand, Limited Supply
While CZT-based scanners aren’t new overall, whole-body scanners of this size are a relatively recent innovation.
CZT has existed for decades, but manufacturing it is notoriously difficult.
“It’s taken a long time to develop it into a scalable manufacturing process,” says Arnab Basu, founding CEO of Kromek.
In the company’s facilities in Sedgefield, England, there are 170 small furnaces in a room Dr. Basu describes as “like a server farm.”
Inside these furnaces, a special powder is heated, melted, and then solidified into a monocrystalline structure.
The entire process takes weeks.
“Atom by atom, the crystals rearrange themselves […] until they are completely aligned,” Basu explains.
The newly formed CZT, a semiconductor, can detect tiny particles of photons in X-rays and gamma rays with incredible precision, like a highly specialized version of the silicon-based, light-sensitive image sensor found in your smartphone camera.
Each time a high-energy photon hits the CZT, it mobilizes an electron, and this electrical signal can be used to create an image. Previous scanner technology used a two-step process, which wasn’t as accurate.
“It’s digital,” Basu clarifies.
“It’s a single-step conversion. It preserves all the important information, like the timing and energy of the X-rays hitting the CZT detector; color or spectroscopic images can be created.”
He adds that CZT-based scanners are currently used for explosive detection in UK airports and for scanning checked baggage at some US airports.
“We expect CZT to be incorporated into the carry-on baggage segment in the next few years.”
The Material of Choice
But getting CZT isn’t always easy.
Henric Krawczynski, of Washington University in St. Louis, has previously used the material in space telescopes attached to high-altitude balloons.
Those detectors can capture X-rays emitted by both neutron stars and plasma around black holes.
Fuente de la imagen, Kromek
Professor Krawczynski needs very thin slices of CZT, 0.8 mm, for his telescopes, as this helps reduce the amount of background radiation they capture, allowing for a clearer signal.
“I’d like to buy 17 detectors new,” he says. “It’s really hard to get them thin.”
Kromek couldn’t help, as Basu says his company currently has high demand.
“We support a huge number of research organizations. It’s very difficult to do a hundred different things. Each research project requires a very particular detector structure.”
For Krawczynski, it’s not a crisis: he says he could use CZT he has from previous research or cadmium telluride, an alternative, for his next mission.
However, there are more pressing issues at the moment.
The next mission was due to launch from Antarctica in December, but “all the dates are shifting,” Krawczynski says, due to the US government shutdown in November.
Many other scientists use CZT.
In the UK, a major upgrade to the Diamond Light Source research center in Oxfordshire will enhance its capabilities through the installation of CZT-based detectors.
Diamond Light Source is a synchrotron that fires electrons around a giant ring at close to the speed of light. Magnets cause these electrons, as they whiz past, to lose energy in the form of X-rays, which are then directed from the ring down beamlines to, for example, analyze materials.
Recent experiments have involved analyzing impurities in aluminum during its melting. Better understanding these impurities could help improve the recycled forms of the metal.
With the Diamond Light Source upgrade, slated for completion in 2030, the X-rays produced will be significantly brighter, meaning existing sensors won’t be able to detect them properly.
“There’s no point in spending all this money upgrading these facilities if you can’t detect the light they produce,” says Matt Veale, leader of the detector development group at the Science and Technology Facilities Council, a stakeholder in Diamond Light Source.
So, CZT is the material of choice here too.
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