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X-ray phase contrast imaging is a very promising technique that may lead to significant advancements in a variety of fields, perhaps most notably, medical imaging. The radiation physics group at University College London is currently developing an x-ray phase contrast imaging technique that works with laboratory x-ray sources. This system essentially measures the degree to which photons are refracted by regions of an imaged object. The amount of refraction that may be expected to be encountered in practice impacts strongly upon the design of the imaging system. In this paper, we derive an approximate expression between the properties of archetypal imaged objects encountered in practice and the resulting distribution of refracted photons. This is used to derive constraints governing the design of the system. OCIS codes: 050.1960, 110.7440, 340.7430.

Preliminary studies have shown the effectiveness of multivariate analysis (MVA) for drug identification from energy-dispersive X-ray diffraction patterns. A statistical model to predict drug content from the diffraction profile of a sample of mixed composition was developed by applying MVA to both experimental and simulated data. Separate data-sets were used for building and testing the models. Both experimental and simulated data were used and the MVA predictions compared. Experimental data included diffraction patterns from small (5 mm diameter) drug samples with various cutting agents, acquired with a HPGe detector; simulated data included diffraction patterns of samples including materials simulating drugs (i.e., materials featuring sharp diffraction peaks in the relevant momentum transfer range) and typical packaging materials. Both a HPGe detector (energy resolution 0.7 keV at 59.5 keV) and a CZT detector (energy resolution 4 keV at all energies) were simulated. MVA was used to predict the drug content. In all cases different statistics were applied to assess the detection limits of the models. Multivariate analysis has proved effective in both identifying the presence of a drug and its concentration. Due to the large contribution to peak broadening given by angular resolution, no significant decrease in accuracy has been found when using CZT with respect to HPGe data. Index Terms--Diffraction, drugs, multivariate analysis, x-ray detectors.

A system for drug detection using X-ray diffraction is currently being developed by the DILAX collaboration. A simulation program for modelling the response of an energy-dispersive X-ray diffraction system has been developed, with the two-fold aim of selecting possible configurations prior to experimental tests and of generating data for statistical models for prediction of drug content. Simulated data showed a good agreement with experimental results. The data showed that the main factor affecting the shape of the diffraction pattern is the thickness of the sample. Scatter angle and detector energy resolution have a smaller effect on the diffraction pattern. This suggests that cheaper, room-temperature detectors can be used for a drug detection system without any loss in sensitivity and specificity. Index Terms--Nondestructive testing, X-ray imaging, diffraction, geometric modelling.

98 SPEAR sensors from eV Products have been evaluated for their use in a portable Compton camera. The sensors have a 5 mm x 5 mm x 5 mm CdZnTe crystal and are provided together with a preamplifier. The energy resolution was studied in detail for all sensors and was found to be 6% on average at 59.5 keV and 3% on average at 662 keV. The standard deviations of the corresponding energy resolution distributions are remarkably small (0.6% at 59.5 keV, 0.7% at 662 keV) and reflect the uniformity of the sensor characteristics. For a possible outside use the temperature dependence of the sensor performances was investigated for temperatures between 15 and 45 deg Celsius. A linear shift in calibration with temperature was observed. The energy resolution at low energies (81 keV) was found to deteriorate exponentially with temperature, while it stayed constant at higher energies (356 keV). A Compton camera built of these sensors was simulated. To obtain realistic energy spectra a suitable detector response function was implemented. To investigate the angular resolution of the camera a [sup.137]Cs point source was simulated. Reconstructed images of the point source were compared for perfect and realistic energy and position resolutions. The angular resolution of the camera was found to be better than 10 deg. Index Terms--CdZnTe, Compton camera, CZT, energy resolution, gamma-ray, imaging, simulation.

I-ImaS (Intelligent Imaging Sensors) is a European project aiming to produce new, intelligent x-ray imaging systems using novel APS sensors to create optimal diagnostic images. Initial systems have been constructed for medical imaging; specifically mammography and dental encephalography. However, the I-ImaS system concept could be applied to all areas of x-ray imaging, including homeland security and industrial QA. The I-ImaS system intelligence is implemented by the use of APS technology and FPGAs, allowing real-time analysis of data during image acquisition. This gives the system the capability to perform as an on-the-fly adaptive imaging system, with the potential to create images with maximum diagnostic information within given dose constraints. The I-ImaS system uses a scanning linear array of scintillator-coupled 1.5-D CMOS Active Pixel Sensors to create a full 2-D x-ray image of an object. This paper describes the parameters considered when choosing the scintillator elements of the detectors. A study of the positioning of the sensors to form a linear detector is also considered, along with a discussion of the potential losses in image quality associated with creating a linear sensor by tiling many smaller sensors. Preliminary results show that the detectors have sufficient performance to be used successfully in the initial mammographic and encephalographic I-ImaS systems that are currently under construction. Index Terms--CMOS, scintillators, x-ray imaging.