UFC - Ultra Fast Ceramic

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. Detector Quantum Efficiency (DQE) 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 < 0.3 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 Healthineers 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 (with 30 kGray).

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 the tab Technology.

Functional ceramics are all-important for high image quality. UFC^™ is a scintillator material which quickly and efficiently transforms radiation from the X-ray tube into light signals. These signals in the visible spectrum are in turn picked up by photodiodes, transforming them into electric signals, which are computed to become visual 2D or 3D images.

Conventionally, other single crystalline substances are used in X-ray detectors such as cadmium tungstate (CdWO4), or cesium iodide (CsI). In our UFC we use a crystal lattice of rare earth compounds gadolinium oxysulfide (GOS). UFC has a large X-ray absorption coefficient and due to its fast decay, reacts very rapidly to changes in X-ray intensity. These properties make it the ideal scintillator not only for time-critical medical imaging, but also for other fields and dynamic applications.

UFC is superior to conventional detector materials in many ways - from light output, to decay time and drift. This outstanding product has proven itself in the challenging field of medical imaging. Now, we see our UFC being used in more and more industries - in order to deliver ever-improving levels of accuracy and efficiency elsewhere.

Due to its fast decay behaviour and extremely short afterglow, Siemens Healthineers UFC scintillator material is optimized for use with the fastest CT scanners, with rotational speeds well under 0.3 seconds.

In high-speed cardiac imaging, UFC requires no compromises in the number of image projections or any other correction algorithms which would impair image quality. UFC's primary advantage is its speed in combination with other unique properties – from minuscule drift, to short afterglow and excellent mechanical behaviour and handling.

Since scanners are becoming increasingly faster, this advantage of fast decay times continues to gain in importance in medical imaging as in other dynamic applications.

1. Properties

1.1 Physical Properties

1.1.1 X-ray and γ - Properties

X-ray Attenuation Coefficient, based on: μ = 1/d ln (I/Io)

Data based on experiments using a CT X-ray tube and filters 3.0 mm Al + 0.6 mm Titan; tungsten anode; attenuation coefficient of a 1.4 mm UFC detector.

Data based on calculations for mono energetic radiation

a) Temporary Radiation Damage (Drift)
Signal change (typical) = 0.4% at 120 kV/250mA; t=60s
1005 mm (focus detector distance). Filter 10 mm Al equivalent at 80kV.

b) Permanent Radiation Damage
No permanent damage observed during 10 years of operation and in measurement
with 30 kGray.

Uniformity of Spectral Linearity
Typical uniformity = 0.025% over a length of 10 mm using the dual energy method:
120 kV/ 194 mAs/ 1005 mm (focus detector) and
140 kV/ 126 mAs/ 1005 mm (focus detector distance)

1.2 Optical Properties

1.2.1 Optical Constants

Refractive index n = 2.2

1.2.2 Point Spread Function (subject to future changes)

Gaussian shape:
FWHM 1) = full width at half maximum
FWTM 2) = full width at tenth maximum


1.2.3 Light Output Uniformity

Light output change < 1% over a length of 30 mm.
Uniform X-ray exposure uncoated ceramic.
Use of a reflector may affect this value.

1.3 Luminescence

1.3.1 Emission Wavelength Spectrum

1.3.2 Short Time Afterglow

UFC

• time 0 for tuning off source is known within ~0.2 ms
• decay to < 10^-3 occurs within 0.2 ms
• a trend to teach 10^-4 is seen at 2.5 - 4 ms

1.3.3 Long - Term Afterglow with Pulsed X-ray Source

• data interval is 1 ms
• decay to 10^-4 is seen after 1 ms and decay to < 10^-5 within 10 ms
• digitization noise becomes relevant below 10^-5
• a trend towards 10^-6 is seen between 10 ms and 100ms

1.4 Bulk Properties

1.4.1 Density

7.29 – 7.33 g/cm³ (99.95% of theoretical density)

1.4.2 Vickers Hardness (subject to future changes)

HV = 910 ± 50 (Force: 1.5 N, duration: 20 s, rate: 20 p/s)

1.4.3 Thermal Properties

Specific Heat Capacity
Cp ≈ 0.318 ± 0.016 Jg^-1K^-1 at 305 K 

Thermal Expansion Coefficient (volume)
10.0 *10^-6 ± 0.3 * 10^-6 K^-1 between 423 K – 873 K 

Thermal change of light output
The average change of light output is 6 GU/K (Temperature = from 301K to 310K) 

Thermal Conductivity
9.6 ± 1.4 Wm^-1K^-1 at 293 K

1.4.4 Electrical Properties

Conductivity (dark)
σ_d< 1 * 10^-13 Ω ^-1 m^-1 

Photoconductivity (at typical light intensities) can be neglected.

2. Handling

2.1 General Resistance

UFC is resistant to all kinds of oil, solvent and water. It dissolves in concentrated mineral acids.

2.2 Weather Resistance

No change in characteristic properties after 3 months at an atmosphere of 100% O₂, a relative humidity of 100% and a temperature of 70 °C (158°F).

2.3 Machining Properties

UFC may be precision machined and processed using all kinds of abrasive methods as sawing, lapping, polishing as well as etching.

2.4 Handling Tools

The UFC needs to be handled according to the rules of good craftsmanship. It may not be handled using smooth metals (up to non-hardened steel). Metallic contaminations are difficult to remove.

2.5 Environmental Safety

Due to its non poisonous nature UFC has no impact on the environment unlike other solid state scintillation materials.

3. Customizing

3.1 Form

Rectangular wafers or crude blocks.

Flatness: < 10 μm

3.3 Surface Roughness

Rz = 2.5 μm – 8 μm

Recently security has become a major issue at airports for baggage control, in public transport and other public locations such courtrooms, embassies and the like. Backscatter X-ray machines that look beneath the clothing can detect hidden weapons, explosives, or illegal substances. Here, fast detector speed is of great importance – UFC is the perfect choice.

The huge volume of cargo passing through airports and cargo controls at harbours, can occasionally be daunting, slowing down processes and causing inconvenience to both passengers and staff. Table-top systems equipped with fast detector technology can speed up screening and enables fast throughput.

Quality assurance and testing are critical in the food industry. Contaminant issues can adversely affect brand image, long-term success of a company and consumer safety. Food processing and packaging requires ongoing analysis of foreign particles (e.g. metal, plastics or glass splinters) and broken or insufficient filled packets.

Through the use of our UFC scintillator material, X-ray technology can identify what is in materials of any kind, sort regardless of their color and contamination, and recycle them. With this technology, substances can be separated according to their atomic weight and density. This makes it possible to separate elements of a material into different material types.

Non-destructive evaluation is becoming more popular in the wood and furniture industries, as precious resources need to be managed carefully and efficiently. Furthermore, various attributes of wood panels largely determine panel end-uses. New design and manufacturing techniques require improved performance and strength of wood panels – which correspond to their density distribution. Automated non-destructive analytical techniques give insights into wood and fibre properties, such as density, allowing a more cost-efficient approach to wood exploitation and furniture production. UFC scintillation materials are robust in handling and fast – boosting your production and your outcome.

Our high-performing UFC^™ and solid screen scintillators are designed, manufactured and assembled to highest standards of quality and performance in our high-tech detector center Forchheim in Southern Germany. Our scientists and engineers continuously work to perfect Siemens Healthineers UFC technology and production processes – at affordable prices.

Scintillation characteristics and quality depend to a high extent on the scintillator manufacturing method, specifically on grain size, powder concentration and other aspects. While we will not give you the exact recipe, here is a short outline of the process starting from highly pure raw material, to ceramics with a pore-free, homogenous crystal structure, to a fully structured array of finest UFC.

Synthesis of the ceramic material

First the basic ceramic raw materials are dissolved in water. They contain rare earth oxysulfides and other compounds. With the application of heat, a chemical transformation takes place. Tiny rod-like crystallites of microscopic size grow from the supersaturated solution. Following the filtering off of water and subsequent drying, a powdered intermediate product results.

In the oven process which then follows, the powder is reduced in a gaseous atmosphere to the actual fluorescing detector material. This compacted powder now consists of the special UFC chemical formula.

Sintering the ceramic material

Scintillator ceramics must be optically translucent to transparent to ensure maximum transmittance of radiation. Only high-density ceramic with extremely low residual porosity, inclusions or grain boundaries (voids) meets this requirement.
 

Pressure-assisted sintering of the powder to a nearby 100% dense, homogeneous ceramic material allows the UFC properties required for detectors to emerge. Densification is achieved at very high temperatures with the simultaneous application of a compressive force of several tons.

Following cool down, the UFC pressed block is cut into wafers on a multi-wire saw with an extremely thin diamond wire. The wafers are then ground to their exact final size. In the next step, their physical characteristics are inspected.

Structuring the array

After the testing of the UFC wafer, a reflector layer is laminated onto it. The wafer is then structured and separated into UFC arrays. Each CT product line has its own requirements in regard to size, number, and layout of the pixels. The required structure is first transferred to the wafer, fully automatically and in two dimensions, using an ultrahigh-precision saw.

The interstitial zones of the pixels and the rear of the array are coated with a special reflecting polymer so as not to lose any of the light produced in the scintillator and to optically separate the pixels. Several tests are carried out to verify conformity with rigorous mechanical and optical tolerances.

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