Sub-pixel energy-weighting techniques for metallic contaminant highlighting in a pharmaceutical hard capsule using a Timepix3 CdZnTe hybrid pixel detector

Abstract

The presented work describes the capabilities of a state-of-the-art spectroscopic photon-counting hybrid pixel detector for use in non-destructive testing, as a contaminant detector with potential uses in the food and pharmaceutical industries. A pharmaceutical hard capsule containing vitamin powder, contaminated with Steel (ST) and Tungsten (W) was prepared under controlled conditions. Both contaminants are distinguished from the powder by combining sub-pixel imaging with spectroscopic imaging analysis, made possible by the use of a 2 mm CdZnTe sensor coupled to a Timepix3 ASIC, operated in Time-over-Threshold and Time-of-Arrival mode. The sub-pixelization technique achieves a spatial resolution of 18.3 μm, with a maximum photon flux of 2.5× 106 photons/s· cm2. For the spectral analysis technique implemented, each energy bin image is energy-weighted, with weights optimally defined by considering the bin contrast and noise behavior, and combined to form an integrated-spectrum enhanced image with increased contaminant visibility. Contrast-to-Noise Ratio (CNR) for each contaminant type was used for performance assessment of the approach. A CNR increase of 106% above the reference unweighted-spectrum image was achieved for the ST contaminant, while the denser W contaminant showed a CNR increase of 80%. This means that the presented spectroscopic imaging technique is feasible for implementation in material visibility enhancement.

Window-Based Energy Selecting X-ray Imaging and Charge Sharing in Cadmium Zinc Telluride Linear Array Detectors for Contaminant Detection

“…On the right side, the material segmentation (black area for steel, gray for coffee and white for plastics) performed on low charge sharing images (G-CSD and CSD images) was in agreement with the ground-truth segmentation; meanwhile, poor segmentation was obtained in the raw images. To quantify the image quality enhancements, we used the well-known contrast-to-noise ratio ( CNR ) [ 6 , 7 , 8 ] as figure of merit, calculated for each ROI selected by the segmentation, as follows: where, I C and I B are the average normalized intensities of the selected contaminant (steel or plastics) and background (coffee), respectively, while σ B is the standard deviation of the background and C C the contrast. The CNR gave a good quantification of the contributes of both contrast and noise in the images.…”

“…The CNR gave a good quantification of the contributes of both contrast and noise in the images. Typically, a CNR ranging between 3–5 is required for an object to be considered detectable [ 6 , 7 , 8 ].…”

“…The importance of energy-resolved photon counting (ERPC) systems for quality enhancements in X-ray images is now widely recognized [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Due to the energy-dependence of the X-ray attenuation processes, spectral X-ray imaging represents a key tool for high resolution material detection and quantitative analysis, especially for medical diagnosis [ 4 , 5 , 9 , 10 ] and non-destructive testing (NDT) in security and food industry [ 6 , 7 , 8 ]. Once the spectral images are acquired, different techniques and algorithms can be easily applied to combine and weight the energy-binned images.…”

“…While the advantages of the energy-resolved approach have been well demonstrated in several studies [ 9 , 10 , 11 , 12 ], the development of ERPC systems with high spatial and energy resolution is still currently under research and development. ERPC prototypes based on room temperature compound semiconductor detectors have given the best results, ensuring direct photon counting detection and good room temperature energy/spatial resolution [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Among these materials, cadmium zinc telluride (CdZnTe or CZT) has reached an excellent maturity level in room temperature X-ray and gamma-ray detection from photon energies of few keV up to 1 MeV [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ].…”

“…ERPC prototypes based on room temperature compound semiconductor detectors have given the best results, ensuring direct photon counting detection and good room temperature energy/spatial resolution [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Among these materials, cadmium zinc telluride (CdZnTe or CZT) has reached an excellent maturity level in room temperature X-ray and gamma-ray detection from photon energies of few keV up to 1 MeV [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Recently, in the framework of the AVATAR X project (funded by the Italian Ministry for University and Research), we developed ERPC systems based on sub-millimetre CZT linear array detectors for contaminant detection in food industry.…”