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By measuring the time of flight of scattered X-ray photons, the point of interaction, assuming a single scatter, can be determined, providing 3-D information about an object under inspection. This paper describes experimental ToF Compton scatter measurements conducted at the versatile electron linear accelerator (VELA), a picosecond pulsewidth electron source situated in Daresbury, U.K. The ToF of scattered X-ray photons was measured using a CeBr3 detector, and a full width at half maximum (FWHM) of between 29  and 36 cm was achieved with a 5-cm-thick plastic test object. By implementing a low-energy cutoff, the FWHM was reduced to between 12 and 26 cm. Two test objects placed in series with a 50-cm space between were separable in the data after applying the low energy cutoff. [ABSTRACT FROM PUBLISHER]

Digital detectors based on complementary metal-oxide-semiconductors (CMOS) active pixel sensor (APS) technology have been introduced recently in many scientific applications. This work is focused on the X-ray performance evaluation of a novel CMOS APS detector in low energy medical imaging applications using monochromatic synchrotron radiation (i.e., 17–35 keV), which also allows studying how the performance varies with energy. The CMOS sensor was coupled to a Thallium-activated structured cesium iodide (CsI:Tl) scintillator and the detector's X-ray performance evaluation was carried out in terms of sensitivity, presampling modulation transfer function (pMTF), normalized noise power spectrum (NNPS) and the resulting detective quantum efficiency (DQE). A Monte Carlo simulation was used to validate the experimentally measured low frequency DQE. Finally, the effect of iodine's secondary generated K-fluorescence X-rays on pMTF and DQE results was evaluated. Good agreement (within 5%) was observed between the Monte Carlo and experimentally measured low frequency DQE results. A CMOS APS detector was characterized for the first time over a wide range of low energies covering the mammographic spectra. The detector's performance is limited mainly by the detectability of the scintillator. Finally, we show that the current data could be used to calculate the detector's pMTF, NNPS and DQE for any mammographic spectral shape within the investigated energies. [ABSTRACT FROM AUTHOR]

A pixellated CdTe detector system comprising 2x2 detector modules has been developed for high energy spectroscopic X-ray imaging applications and has an active area of 16 cm^2. The detector modules are made from the HEXITEC 80x80 ASIC and 1 mm thick CdTe with Al-Schottky contacts. The CdTe has 250 \mum pitch pixels with an outer guard ring on the same pitch. The single HEXITEC 80x80 detectors have an average energy resolution (FWHM) of 800 eV at 59.9 keV. Limitations in the multiple module DAQ system mean that the energy resolution of the pixels in the 2x2 detector array is 2.0 keV at 59.9 keV. The spacing between the tiled detector modules is 150 \mum which results in an inactive area equivalent to 3 pixels, including the guard ring on the edge of the detectors. The modular detector configuration demonstrates the potential to create large area detector arrays in the future. [ABSTRACT FROM PUBLISHER]

Intervertebral disc degeneration is an age-associated condition related to chronic back pain, while its consequences are responsible for over 90% of spine surgical procedures. In clinical practice, MRI is the modality of reference for diagnosing disc degeneration. In this study, we worked toward 2-D semiautomatic segmentation of both normal and degenerated lumbar intervertebral discs from T2-weighted midsagittal MR images of the spine. This task is challenged by partial volume effects and overlapping gray-level values between neighboring tissue classes. To overcome these problems three variations of atlas-based segmentation using a probabilistic atlas of the intervertebral disc were developed and their accuracies were quantitatively evaluated against manually segmented data. The best overall performance, when considering the tradeoff between segmentation accuracy and time efficiency, was accomplished by the atlas-robust-fuzzy c-means approach, which combines prior anatomical knowledge by means of a rigidly registered probabilistic disc atlas with fuzzy clustering techniques incorporating smoothness constraints. The dice similarity indexes of this method were 91.6% for normal and 87.2% for degenerated discs. Research in progress utilizes the proposed approach as part of a computer-aided diagnosis system for quantification and characterization of disc degeneration severity. Moreover, this approach could be exploited in computer-assisted spine surgery. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

98 SPEAR sensors from eV Products have been evaluated for their use in a portable Compton camera. The sensors have a 5 mm × 5 mm × 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 137Cs 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. [ABSTRACT FROM AUTHOR]