In 1895, when Wilhelm Roentgen was first developing the X-ray, his wife exclaimed that she had “seen her death” upon being shown a ghostly image of her hand. X-rays have fascinated and terrified us ever since. As early as 1897, a short film showing a couple ‘transformed’ into X-rays engrossed British audiences. In part, this allure was tinged by danger, with Marie Curie, Elizabeth Fleischman and several other pioneers dying of radiation poisoning. It hardly helped that, until the 1930s, X-ray machines were operated by untrained amateurs. The reputation of X-rays have changed substantially, as they now play a central role in medical life. NHS England carries out 22.2 million procedures each year and in the US, between 2000 and 2010, 35% of emergency room visits included an X-ray, while the use of advanced imaging scans (CT or MRI) increased from 5% of visits to 17%.
At the same time, the early dangers of X-rays have fallen away; however, doctors are careful to limit the number that patients can have each year. Meanwhile, X-ray technology has grown in popularity. Over the past 30 years, CT and MRI scans have provided doctors with an unimaginable level of detail about how our bodies work, while new PET scans are able to pinpoint cancer cells with remarkable accuracy.
Despite these jumps forward, there are still striking limitations to current X-ray technology. For one thing, it is difficult to measure the amount of radiation that enters a patient, especially during radiotherapy. The smallest X-rays tend to sacrifice image quality and bigger ones are unsuitable for invasive procedures, such as endoscopy. Happily, a team of researchers in eastern France may have made a major breakthrough.
Making light work of innovation
For over a decade at the FEMTO-ST Institute, Thierry Grosjean has covered everything from optical fields to plasmonic wave guides. Since it was founded in 2004, the institute has made notable contributions to the industry’s understanding of optics and nanoscience, and is now one of the top French research facilities.
For his latest project, Grosjean decided to keep things simple by using the humble horn antenna, which was invented in 1897. “This sort of antenna is commonly used to, for instanace, emit microwaves or radio frequencies,” explains Grosjean. “We transposed this horn to optics to develop new functionalities. I had the idea to develop an optical horn antenna to control the emission of scintillators.”
This is an important step forward. Scintillators – the detectors that absorb X-rays – emit light to optical cameras and launch light photons in all directions. This is not a problem at larger sizes, but smaller scintillators emit so few photons that cameras struggle to absorb enough to work properly. By adding an optical horn antenna to the scintillators, Grosjean and his team were able to control the direction of light emissions. This ensured that the small number of photons emitted from the scintillator were sent in the right direction.
While fixing the scintillators was a vital part of Grosjean’s work, it was by no means his only challenge. After being directed by the horn antenna, light from the scintillators needed to continue up the fibre before finally ending up as an image on a computer. Luckily, Grosjean’s antenna proved ideal for this task too. “The light that is channelled by the antenna is efficiently transferred into the fibre,” he says. “We can launch the light into the fibre, but the fibre can possibly not emit the light. We need these phase-matching properties. A typical property of this antenna is to be able to efficiently convert the light into the fibre.” Overall, Grosjean adds, the antenna has two purposes. “The first is to have a highly directional emission from the scintillator towards the fibre. The second is to phase match optical radiation into the fibre.”
Small change
All of this would be impressive, whatever the size. As it is, Grosjean’s work is particularly remarkable thanks to its miniscule proportions. After all, the fibre he used was just 125μm wide and his team hope to get this down to less than 100μm. So far, his system has only been tested with low-energy X-rays, not the more powerful type that are common in medical practice. In addition to using high-energy X-rays, Grosjean also plans to drastically improve patient care; one of the most thrilling possibilities is that the technology could be used in endoscopy, especially to measure radiation levels during radiotherapy.
“One of the applications could be as a dosimeter,” states Grosjean. “The point is that the fibre is very small, and our detector is smaller than others that are currently available and we can use this in endoscopic applications.
“We can insert it into the body of the patient, then put a detector in contact with the tumour, and monitor the dose that is really going onto the tumour, causing minimal problems for the patient because it’s so tiny.”
This scheme could improve radiotherapy in other ways too. As the fibre is so small, and the antenna so targeted, radiation can be sent directly and accurately to a cancer tumour. This would greatly improve on the current approach, where X-rays are fired like buckshot into an infected area, often hitting harmless tissue in the process. A related advantage is that patients would absorb less radiation during treatment, reducing the dangers of crippling side effects, such as hair loss and infertility. At the same time, the researchers are investigating whether their technology could potentially improve the speed at which X-rays are detected. “An intrinsic property of the optical antennas is that they reduce the time between the absorption of radiation and emission of light,” says Grosjean. “The antenna should reduce the delay between the absorption of the X-ray and the emission of light. This is particularly interesting for X-ray detection, given that detectors are pretty slow at the moment. We have the possibility of improving detection speeds.”
Accessible technology: benefits for hospitals and cancer patients
But if all these advances are exciting in theory, they are useless until they can escape the lab and enter hospitals. Grosjean and his team are clearly aware of this, and have designed their technology with accessibility in mind. For instance, they picked a simple optical fibre for their experiments, like the ones used in telecoms. Elsewhere, the team’s decision to use a horn antenna once again proved handy. “A challenge that we had at the beginning was to develop an optical antenna that was cheap to realise,” Grosjean explains. “Usually, optical antennas are very difficult to develop and are expensive, but here we wanted to develop a version that was cheap and easy to make. That’s why we chose the horn antenna. It’s pretty easy, cheap and can be mass-produced.”
This new technology also has another advantage: longevity. Regular X-rays risk being damaged if the scintillator comes into contact with the machine’s electronics, which is something that is not possible in Grosjean’s set-up. “The scintillator is far away from the optical detector,” he says. “This is because at one end, the photons have to be detected and are then transferred into an electronic signal. Because of this, the scintillator is far away from the detector, so the electronics are not immersed in the X-rays and get damaged.”
All of this means that Grosjean’s X-rays are cheap and durable, which is something that is extremely useful outside of the academy. Two companies are interested in mass-producing his invention, while hospitals are eager to test it out. By working with the radiotherapy centre at Besançon, and a consortium of other physicists, Grosjean is certainly keen to put his work to practical use. “We’re interested in making the connection between physical research – my area – and the medical domain,” he affirms. “We’ve also applied to get some funding from agencies to develop a medical prototype for the first tests and we’re waiting for a response. We would like to develop a fibre ready for medical applications in three years.”
There is still a way to go until patients will be able to benefit from Grosjean’s technology in the field; however, based on the results so far, there is plenty to be hopeful about. Even a century after its invention, it is nice to see the horn antenna being put to good use.
