A material so extraordinary, yet so elusive to produce, that it's revolutionizing medical imaging and beyond.
Imagine lying motionless in a hospital scanner, arms raised, for a grueling 45 minutes. That was the reality for patients at Royal Brompton Hospital in London until last year, when a new device arrived, slashing scan times to a more manageable 15 minutes.
The secret? A special material called cadmium zinc telluride (CZT), crafted by the British company Kromek, one of a select few worldwide with this expertise. CZT enables the scanner to create highly detailed, 3D images of patients' lungs, a true marvel of engineering and physics, as Dr. Kshama Wechalekar, head of nuclear medicine and PET, puts it.
But CZT's applications extend far beyond medical imaging. It's used in X-ray telescopes, radiation detectors, and airport security scanners, and its demand is on the rise.
Dr. Wechalekar and her team use CZT-based scanners to investigate patients' lungs, searching for tiny blood clots in long Covid cases or larger clots known as pulmonary embolisms. The £1m scanner works by detecting gamma rays emitted by a radioactive substance injected into patients' bodies, and its sensitivity allows for a 30% reduction in the dose required.
CZT has been around for decades, but its manufacturing process is notoriously challenging. Arnab Basu, founding CEO of Kromek, explains that it took a long time to develop an industrial-scale production method. In Kromek's facility, 170 small furnaces work together to transform a special powder into a single-crystal structure, a process that takes weeks.
The resulting CZT, a semiconductor, can detect tiny photon particles in X-rays and gamma rays with exceptional precision, akin to the light-sensing image sensor in your smartphone camera but highly specialized. When a high-energy photon strikes the CZT, it mobilizes an electron, generating an electrical signal that can be used to create an image.
"It's digital, a single conversion step," says Dr. Basu. "It retains all the important information, such as timing and the energy of the X-ray hitting the CZT detector. You can create color or spectroscopic images."
CZT-based scanners are already in use for explosives detection at UK airports and for scanning checked baggage in some US airports. Dr. Basu predicts that CZT will soon be used for hand luggage scanning as well.
However, acquiring CZT is not without its challenges. Henric Krawczynski, a professor at Washington University in St. Louis, has used CZT in space telescopes attached to high-altitude balloons to detect X-rays emitted by neutron stars and plasma around black holes. Prof. Krawczynski requires very thin, 0.8mm pieces of CZT to reduce background radiation and obtain a clearer signal.
"We'd like to buy 17 new detectors, but it's really difficult to get these thin ones," he says.
Prof. Krawczynski was unable to source CZT from Kromek due to high demand. Kromek supports many research organizations, and each research project requires a very specific type of detector structure, making it challenging to accommodate all requests.
But the challenges don't end there. Prof. Krawczynski's upcoming mission, scheduled to launch from Antarctica in December, is now in flux due to the US government shutdown.
CZT is also in high demand among scientists. The Diamond Light Source research facility in Oxfordshire, UK, is undergoing a half-billion-pound upgrade that 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 nearly the speed of light, and magnets cause these electrons to emit X-rays, which are then used to analyze materials.
Recent experiments have involved studying impurities in melting aluminum, which could lead to improvements in recycled metal forms. With the upgrade, the X-rays produced will be significantly brighter, and CZT is the material of choice to detect these enhanced signals.
"There's no point in spending all this money if you can't detect the light they produce," says Matt Veale, group leader for detector development at the Science and Technology Facilities Council.
CZT, a wonder material with a challenging production process, is transforming medical imaging and scientific research, but its limited availability presents a unique set of challenges.
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What do you think? Is CZT's potential worth the manufacturing challenges? Share your thoughts in the comments!
