Scientists create CMOS sensors to capture X-rays

Scientists have created one of the largest CMOS imaging sensors capable of capturing X-rays, gamma rays and other radiation.

At 12.8 cm2 it offers increased sensitivity and dynamic range, as well as reduced noise and could, therefore, potentially improve medical imaging such as cancer screening.

Conventional radiation imaging, including X-ray mammography, requires film plates which the radiographer removes and examines.

In recent years there has been increased use of digital radiography, which uses amorphous silicon panels rather than film. While offering advantages in terms of record keeping, it has not been shown to be significantly better than conventional film imaging in terms of resolving power.

Now researchers at Lincoln University have developed a device termed DynAMITe that uses a complementary metal-oxide-semiconductor (CMOS) sensor with a scintillator to convert the X-ray/gamma rays into visible light.

DynAMITe can be doubled up to give a total area of 25.6 cm2 so it can cover whole body areas such as the chest without the need for lenses to focus the image on the detector.

‘If you put light through a lens system you lose a lot, it’s very inefficient — in a typical lens system only a few per cent of the photons will actually get through, so it becomes less sensitive,’ Prof Nigel Allinson of Lincoln told The Engineer.

In addition, the sensor pixels — which consist of photodiodes and associated gated circuitry — are between 50–100 microns across and spaced around 50 microns apart. This compares with pixels of around 3–6 microns packed closely together in consumer digital cameras, thus giving DynAMITe high sensitivity and reduced noise.

‘This gives us enormous dynamic range — we can see very faint objects and very bright objects with the same camera,’ Allinson said.

The team also designed the DynAMITe sensor to be resistant to the radiation it is designed to collect.

‘As it will withstand exposure to very high levels of X-ray and other radiation, it will operate for many years in the adverse environment of cancer diagnosis and treatment instruments,’ said Allinson, adding that DynAMITe would be useful for guiding the new generation of proton beam therapies.