C Christodoulou

Pixellated Cd(Zn)Te high-energy X-ray instrument

We have developed a pixellated high energy X-ray detector instrument to be used in a variety of imaging applications. The instrument consists of either a Cadmium Zinc Telluride or Cadmium Telluride (Cd(Zn)Te) detector bump-bonded to a large area ASIC and packaged with a high performance data acquisition system. The 80 by 80 pixels each of 250 μm by 250 μm give better than 1 keV FWHM energy resolution at 59.5 keV and 1.5 keV FWHM at 141 keV, at the same time providing a high speed imaging performance. This system uses a relatively simple wire-bonded interconnection scheme but this is being upgraded to allow multiple modules to be used with very small dead space. The readout system and the novel interconnect technology is described and how the system is performing in several target applications.

A quantitative x-ray detection system for gold nanoparticle tumour biomarkers

X-ray fluorescence techniques have proven beneficial for identifying and quantifying trace elements in biological tissues. A novel approach is being developed that employs x-ray fluorescence with an aim to locate heavy nanoparticles, such as gold, which are embedded into tissues. Such nanoparticles can be functionalized to act as markers for tumour characteristics to map the disease state, with the future aim of imaging them to inform cancer therapy regimes. The uptake of functionalized nanoparticles by cancer cells will also enable detection of small clusters of infiltrating cancer cells which are currently missed by commonly used imaging modalities. The novel system, consisting of an energy-resolving silicon drift detector with high spectral resolution, shows potential in both quantification of and sensitivity to nanoparticle concentrations typically found in tumours. A series of synchrotron measurements are presented; a linear relationship between fluorescence intensity and gold nanoparticle (GNP) concentration was found down to 0.005 mgAu ml(-1), the detection limit of the system. Successful use of a bench-top source, suitable for possible future clinical use, is also demonstrated, and found not to degrade the detection limit or accuracy of the GNP concentration measurement. The achieved system sensitivity suggests possible future clinical usefulness in measuring tumour uptake in vivo, particularly in shallow tumour sites and small animals, in ex vivo tissue and in 3D in vitro research samples.

K-edge subtraction imaging using a pixellated energy-resolving detector

This paper presents preliminary work aimed at assessing the feasibility of K-edge subtraction imaging using the spectroscopic information provided by a pixellated energy-resolving Cadmium Zinc Telluride detector, having an active area of 20×20 pixels 250 μm in size. Images of a test object containing different amounts of Iodine-based contrast agent were formed above and below the K-edge of Iodine (33.2 keV) by integrating, pixel by pixel, different windows of the spectrum. The results show that the optimum integration window for details 1-2 mm in diameter is between 2 keV and 5 keV. Concentrations of down to 50 μg Iodine/ml were detected in a 1-mm diameter tube with an entrance dose of 100 μGy.

Identification of simulants for explosives using pixellated X-ray diffraction

A new method of material identification has been developed utilising pixellated X-ray diffraction (PixD) to probe the molecular structure of hidden items. Since each material has a unique structure, this technique can be used to “fingerprint” items and has significant potential for use in security applications such as airport baggage scanning. The pixellated diffraction technique allows two distinct forms of diffraction, angular-dispersive and energy-dispersive X-ray diffraction, to be combined, exploiting the benefits of both. Thus, fast acquisition times are possible with a small system which contains no moving parts and can be easily implemented. In this work, the capability of the system to identify specific materials within a sample is highlighted. Such an approach would be highly beneficial for detecting explosive materials which are concealed amongst or inside other masking items. The technology could easily be added to existing baggage scanning equipment and would mean that if a suspicious item is seen in a regular X-ray image, the operator of the equipment could analyse the object in detail without opening the bag. The net result would be more accurate analysis of baggage content and faster throughput, as manual searching of suspicious objects would not be required.

Materials identification using a small-scale pixellated x-ray diffraction system

A transmission x-ray diffraction system has been developed using a pixellated, energy-resolving detector (HEXITEC) and a small-scale, mains operated x-ray source (Amptek Mini-X). HEXITEC enables diffraction to be measured without the requirement of incident spectrum filtration, or collimation of the scatter from the sample, preserving a large proportion of the useful signal compared with other diffraction techniques. Due to this efficiency, sufficient molecular information for material identification can be obtained within 5 s despite the relatively low x-ray source power. Diffraction data are presented from caffeine, hexamine, paracetamol, plastic explosives and narcotics. The capability to determine molecular information from aspirin tablets inside their packaging is demonstrated. Material selectivity and the potential for a sample classification model is shown with principal component analysis, through which each different material can be clearly resolved.

A system for x-ray diffraction and fluorescence imaging of nanoparticle biomarkers

Both x-ray diffraction and x-ray fluorescence techniques have proven beneficial for identifying and characterizing biological tissues. X-ray diffraction analysis uses the elemental composition of the sample to discriminate between tissue types, and can provide a considerable enhancement in contrast over conventional x-ray imaging. X-ray fluorescence, in this case, is being used to locate the presence of nanoparticles, such as gold, which are embedded into tissues as biomarkers to map the disease state. A novel system is being developed which combines these two techniques in order to locate tumours and provide information on the tumour characteristics. A series of preliminary fluorescence and diffraction measurements were made over a range of gold nanoparticle concentrations using the SYRMEP beamline at the Elettra synchrotron, Italy. The novel system, consisting of an energy resolving silicon drift detector with high spectral resolution and a polycapillary optic angular collimator, showed potential in both quantification of and sensitivity to nanoparticle concentrations typically found in tumours. The signal from each technique was found to be linear with nanoparticle concentration down to the minimum detectable limit. We found a linear relationship between fluorescence intensity and concentration down to 3.2 ppm by weight. Such system sensitivity suggests usefulness in measuring tumour uptake in vivo. However, both the x-ray fluorescence and diffraction signals are small, and will benefit from an increase in counting statistics and a reduction of the noise.

X-ray edge subtraction imaging of gold nanoparticle concentrations for biological imaging

Nanoparticles may be used as biomarkers to locate tumours and provide information on tumour characteristics. This paper reports on the development of a high resolution imaging system sensitive to gold nanoparticle concentration and distribution and possibly to cell structure.