Space technology can be used for better breast scans

There’s a world of difference between a small cancer tumour in a breast and a violent collision between two neutron stars far out in the universe. But they do have something in common: they’re hard to detect and locate accurately. And Irfan Kuvvetli has invented a detector that can solve this exact problem.

As a senior researcher at DTU Space, he helps develop instruments for space telescopes, and he has specialized in detectors that can detect gamma radiation. This kind of extremely energy-rich electromagnetic radiation is otherwise difficult to get hold of, because it tends to pass right through everything. The new detector makes it possible to ‘capture’ more of the gamma radiation.

“Our detector is a bit like the camera in a mobile phone. Both capture electromagnetic radiation, i.e. photons. The difference is that while the detector in the mobile camera is designed to pick up visible light, our gamma detector has to register radiation with much lower wavelength and higher energy. It’s harder because when the photons have more energy, it takes more to stop them,” says Irfan Kuvvetli.

Astrophysicists are very keen to measure gamma radiation from distant celestial bodies, because it’s often emitted in connection with some of the universe’s most intense and enigmatic events. When a star explodes as a supernova or two neutron stars collide, gamma radiation is emitted, and with the right detector, astrophysicists can not only calculate where the radiation comes from, but also measure its energy. Among other things, this can help them discover how different chemical elements are formed and spread in the universe.

Small cancer tumours light up

But gamma radiation is also used in healthcare. High doses of radiation can kill cancer cells, and certain types of cancer are therefore treated with gamma rays. In addition, gamma radiation from radioactive trace elements can be used to examine different organs. For these reasons, DTU Space was invited to collaborate with the British company Kromek, which manufactures radiation detectors for the pharmaceutical industry. The purpose of the collaboration is to develop an imaging device for diagnostic breast scans based on DTU’s patented technology.

The project is called 3D-MBI—the last three letters stand for Molecular Breast Imaging. The researchers hope they can develop a scanning method that can serve as a supplement to the traditional mammogram examinations.The idea is to make a possible cancer tumour light up in images taken with the new type of gamma camera. Before the examination, the woman is injected with a very small amount of a radioactive tracer, which mainly accumulates in cancer cells. The tracer in the cancer tumour emits gamma radiation, which easily passes through the breast tissue and out to the gamma detector.

The technology makes it possible to detect very small tumours, and it’s hoped that DTU’s detector will make it possible to map the position of the tumour in three dimensions so precisely that a biopsy can be taken immediately, and the cancer can be treated more effectively.

The method is particularly effective when it comes to detecting tumours in women with dense breast tissue. These women are at higher risk of breast cancer, and the cancer is harder to detect with mammograms. According to researchers from Rigshospitalet and the University of Copenhagen, fewer than half of cancer tumours are detected with mammograms of women with very dense breast tissue, and for this group a more effective screening technology can make a big difference.

Benefits of the new design

Gamma detectors are already available for studying outer space, and in hospitals, but the DTU researchers’ design has a number of advantages over the existing detectors. It is based on a mixture of cadmium, zinc, and telluride, because crystals of these three metals form a semiconductor material with the exact right properties to detect X-ray and gamma radiation.

These relatively heavy elements stop the energy-rich radiation quite efficiently, and in addition, cadmium zinc telluride, or CZT, works well at room temperature. Other detectors, for example those based on germanium, only work at very low temperatures and have to be cooled with liquid nitrogen; this is not necessary with CZT.

The CZT crystals are grown in Kromek’s branch in Pennsylvania, where Brian Harris leads the development of the detectors. He says of the collaboration with DTU:

“Irfan’s group at DTU has a long and documented history of detector design and characterization of CZT. The collaboration with DTU has been very beneficial when it comes to knowledge sharing and engineering development tasks.”

Measures each photon

Kromek already manufactures radiation detectors based on CZT, but DTU researchers have figured out how to get as much information as possible out of the gamma rays that are directed at the material.

“We measure every single photon—its energy as well as the time and position of the interaction with the detector material. And when different interactions occur, we can determine where the gamma radiation comes from,” says Irfan Kuvvetli, who has had good experiences working with a private company:

“The collaboration with Kromek meant that we could quickly develop the detector and the associated electronics. After just two years, we now have a detector module that’s ready to be tested and approved for a space mission. It would normally take between three and five years to get this far.”

In fact, while the detector modules are becoming more precise, their structure is also becoming simpler, since fewer electrodes are needed to connect the CZT crystal to the electronics that handle the signal processing.

Better resolution with fewer electrodes

Each time a gamma photon interacts with the detector material, an electrical signal is generated, which is picked up by electrodes attached to the crystal. In conventional detectors, a great many electrodes are needed if you want to know the exact position and the energy allocated for the interaction, but at DTU Space the researchers set out to investigate whether fewer electrical channels could be used. The idea was to use a special algorithm to analyse the signals from all electrodes simultaneously instead of looking at each electrode separately.

“The idea works amazingly well. Our detector module has a minimal number of electrical channels, while having a spatial and temporal resolution capability that other detectors can’t compete with,” says Irfan Kuvvetli and continues:

“If we’re to have a positional resolution capability better than one millimetre for a gamma detector measuring 40 mm x 40 mm x 5 mm, then for a regular pixel detector you need five layers of 1 mm each, and for each layer there must be 40 x 40 electrical channels—8,000 in total. We’ve done this with 53 electrical channels.”

Fewer channels in the so-called strip design lead to simpler and thus cheaper detector modules, and this is important for a detector manufacturer such as Kromek:

“Replacing pixel designs with strip designs greatly reduces the requirements for readout electronics, leading to significantly lower system costs,” says Brian Harris, who also notes that the new design makes it easier to compensate for irregularities in the detector crystal.

Now the researchers at DTU Space are in the process of testing the new detector modules that Kromek has manufactured according to the instructions from DTU Space. And while the DTU researchers are working on an instrument for a future space telescope, Kromek can begin to develop a prototype medical scanning device that can be tested on patients.