High X-ray absorption
The ceramic scintillator absorbs the X-ray quanta and simultaneously converts them to visible light (photons) which is then converted to electrical signals by the optical sensor system. This whole process must be as efficient as possible: The greater the efficiency of this process, the better the detector. DQE or Detector Quantum Efficiency is the yardstick by which the performance of absorber materials is measured.
Exceptionally high overall absorption efficiency is achieved by high X-ray absorption combined with extremely efficient conversion of X-ray energy into visible light. The optical emission spectrum extends from around 500 to beyond 800 nm, ideal for coupling to photodiodes. This superb overall quantum efficiency in conjunction with the unique short afterglow enables time-critical X-ray detection at low doses and extremely fast data collection.
During X-ray conversion, the ceramic scintillator itself begins to glow. The faster it becomes “dark” again, the sooner it is able to convert new radiation, i.e. changes in X-ray attenuation, to light without secondary effects. UFC detectors are optimized for our fastest CT scanner of rotational speeds of < 0.4 seconds. Only scintillators with fast decay can absorb and pass on all the information from multi-slice projections, enabling a higher temporal resolution.
Essentially this means faster processing of signals – which is also important when it comes to real-time X-ray analysis of products in manufacturing at high line speeds.
High detection sensitivity and high conversion efficiency from X-ray to visible light are the prerequisites for superior image quality at low radiation doses. The more X-ray quanta are detected and converted to light output, the more accurate the results and the less 'noise' shows up in CT images as artefacts or blurs. Apart from the actual properties and type of scintillator material, production quality and purity play an important role for spatial resolution.
More spatial resolution of a CT scanner means more detailed the images and smaller possible lesions that can be recognized. The number of pixels – calculated by multiplying the number of detector channels with that of detector lines – determines image resolution. Siemens high-precision manufacturing technologies enable us to obtain this large number of pixels per square cm of highly pure scintillation material needed for multislice CT.
Last but not least, light output should remain stable under long-term or repeated exposure of X-rays. Our UFC scintillators have excellent drift behaviour compared to other materials; no permanent damage at all could be observed after 10 years of operation (at 30 kGray).
Easy handling and customizing
In addition to its minimal afterglow and high absorption properties, UFC shows additional advantages: it can be processed with tools from the silicon industry and for instance cut into stamp-sized plates or other geometrical shapes to meet your special detector requirements and applications. All kinds of techniques may be applied to produce the desired shape, such as sawing, lapping and polishing. This allows precise forming and customizing for superior results.
Moreover, the UFC scintillation material is easy to handle due to its resistance to ambient air, humidity, water, temperature and numerous chemicals such as oils and solvents (other detector materials are hygroscopic and must be sealed). Furthermore, UFC is a non-poisonous material that does not contain any toxic elements as other solid state scintillation materials do, it has no adverse environmental impact.
For technical specifications please go to UFC - Technology