- X-ray photo of frog's legs made with the first Medipix detector
In high-energy physics, special detectors make it possible to observe subatomic particles that are invisible to the human eye.
A particle detector can observe each individual proton, electron, neutron or other exotic particle that falls within its measurement range. Medipix combines this principle with X-ray imaging so that more accurate photos can be made. Additional benefits are that the images are free of noise and that less radiation is needed to produce a photo of a comparable quality to conventional methods.
Detectors without noise
In the mid-1990s, particle physicists working on detection methods for the new LHC particle accelerator at CERN discovered that the Medipix-detector was sensitive enough to detect X-rays as well. Four universities, including those of Pisa and Freiburg, subsequently decided to cooperate on the development of a detector that was suitable for medical applications: Medipix 1.
The first Medipix chip counted each light particle (photon). Whereas in conventional methods several photons are needed to obtain a (black) image, the Medipix chip requires just one and, therefore, requires less radiation. Another important advantage compared to conventional techniques is that no signal whatsoever is measured if no photon enters. This means that there is no noise irrespective of the period of exposure.
At the end of the 1990s, 17 research institutes in Europe and North America, including Nikhef, started a partnership to improve the Medipix 1. This led to the development of the Medipix 2 chip, which contains 256 x 256 pixels and is, therefore, even more accurate still.
Thanks to this partnership between research institutes and the commercial sector, such as that entered into by Nikhef in 2000 with Panalytical, Medipix 2 has found various practical applications.
Medipix 3
- X-ray photo of a sardine
Panalytical is specialised in the development and production of measurement instruments for the analysis of various materials for purposes such as quality tests. X-ray detection makes it possible to distinguish different crystal structures. The pharmaceutical industry can use this approach to check that no contaminants enter medicinal products during the production process. Similar applications are also possible in the steel and cement industries due to the ease with which contaminants can be detected.
By involving Panalytical in the project, Medipix combines scientific insights with the practical mindset of the commercial sector. This benefits both the quality and applicability of the product.
In 2005, the partnership was continued in an altered form to develop the third Medipix chip, a technically advanced version of the second chip. Unlike Medipix 2, Medipix 3 not only counts all of the photons but it also determines the energy level of each individual photon detected. This means that it is also possible, for example, to examine the cogs of a watch from behind its metal casing. Such a chip is useful in astronomy. Less prominent stars can still be observed due to the lower level of noise.
The universities of Freiburg, Glasgow, Naples and Pisa set up a partnership to develop the Medipix-1 chip that emerged from research in the field of high-energy physics. The chip is extremely accurate and sensitive for X-rays, which makes it highly suitable for medical applications. This chip contains 65 X 65 pixels and is about 1.2 cm in size.
For further information, please contact Jan Visschers.
