F. Krejci

Hard x-ray phase contrast imaging using single absorption grating and hybrid semiconductor pixel detector.

A method for x-ray phase contrast imaging is introduced in which only one absorption grating and a microfocus x-ray source in a tabletop setup are used. The method is based on precise subpixel position determination of the x-ray pattern projected by the grating directly from the pattern image. For retrieval of the phase gradient and absorption image (both images obtained from one exposure), it is necessary to measure only one projection of the investigated object. Thus, our method is greatly simplified compared with the phase-stepping method and our method can significantly reduce the time-consuming scanning and possibly the unnecessary dose. Furthermore, the technique works with a fully polychromatic spectrum and gives ample variability in object magnification. Consequently, the approach can open the way to further widespread application of phase contrast imaging, e.g., into clinical practice. The experimental results on a simple testing object as well as on complex biological samples are presented.

High-contrast X-ray micro-radiography and micro-CT of ex-vivo soft tissue murine organs utilizing ethanol fixation and large area photon-counting detector.

Using dedicated contrast agents high-quality X-ray imaging of soft tissue structures with isotropic micrometre resolution has become feasible. This technique is frequently titled as virtual histology as it allows production of slices of tissue without destroying the sample. The use of contrast agents is, however, often an irreversible time-consuming procedure and despite the non-destructive principle of X-ray imaging, the sample is usually no longer usable for other research methods. In this work we present the application of recently developed large-area photon counting detector for high resolution X-ray micro-radiography and micro-tomography of whole ex-vivo ethanol-preserved mouse organs. The photon counting detectors provide dark-current-free quantum-counting operation enabling acquisition of data with virtually unlimited contrast-to-noise ratio (CNR). Thanks to the very high CNR even ethanol-only preserved soft-tissue samples without addition of any contrast agent can be visualized in great detail. As ethanol preservation is one of the standard steps of tissue fixation for histology, the presented method can open a way for widespread use of micro-CT with all its advantages for routine 3D non-destructive soft-tissue visualisation.

Single grating method for low dose 1-D and 2-D phase contrast X-ray imaging

X-ray phase contrast imaging (XPCI) using a single absorption grating and a hybrid semiconductor pixel detector is a newly introduced approach with great potential for application in medicine, biology and material research. In comparison with a conventional grating interferometer technique, which requires a multiple-exposure (phase-stepping) procedure, our method is greatly simplified, because both phase gradient and absorption images are obtained from just one exposure. Consequently, the approach can significantly reduce the time-consuming scanning and also possibly the unnecessary dose. Examples of application of the single-grating approach as an imaging tool for investigations in biology are presented. Particularly, we present the extension of our 1-D single grating method to a two-direction sensitive technique. The novel 2-D sensitive XPCI method is based on precise sub-pixel position determination of the X-ray pattern projected by the two-dimensional transmission grating directly from the pattern image. In a single exposure, phase gradient images in two perpendicular directions together with the conventional attenuation image are produced. Results of the proof-of-concept experiment are presented.

X-ray inspection of composite materials for aircraft structures using detectors of Medipix type

This work presents an overview of promising X-ray imaging techniques employed for non-destructive defectoscopy inspections of composite materials intended for the Aircraft industry. The major emphasis is placed on non-tomographic imaging techniques which do not require demanding spatial and time measurement conditions. Imaging methods for defects visualisation, delamination detection and porosity measurement of various composite materials such as carbon fibre reinforced polymers and honeycomb sendwiches are proposed. We make use of the new large area WidePix X-ray imaging camera assembled from up to 100 edgeless Medipix type detectors which is highly suitable for this type of measurements.

Modular pixelated detector system with the spectroscopic capability and fast parallel read-out

A modular pixelated detector system was developed for imaging applications, where spectroscopic analysis of detected particles is advantageous e.g. for energy sensitive X-ray radiography, fluorescent and high resolution neutron imaging etc. The presented system consists of an arbitrary number of independent versatile modules. Each module is equipped with pixelated edgeless detector with spectroscopic ability and has its own fast read-out electronics. Design of the modules allows assembly of various planar and stacked detector configurations, to enlarge active area or/and to improve detection efficiency, while each detector is read-out separately. Consequently read-out speed is almost the same as that for a single module (up to 850 fps). The system performance and application examples are presented.

Semiconductor pixel detector with absorption grid as a tool for charge sharing studies and energy resolution improvement

A novel approach for characterization of semiconductor pixel detectors using X-rays is presented. A precise gold grid placed in front of the sensor chip segments the incoming X-ray beam into a matrix of precisely defined micro-beams irradiating all pixels in well-defined positions. Analysis of the resulting moire pattern allows evaluation of the charge sharing effect and determination of its influence on the spectrometric properties of the detector. As opposed to currently used single micro-beam studies realized at synchrotron sources, the whole pixel matrix is investigated at once. This offers a great tool for the investigation of charge sharing phenomena and verification of theoretical models used to describe these detectors. Similarly, such an absorption grid can be used for masking the pixel borders thus suppressing the charge sharing effect. As we demonstrate, this approach significantly improves the spectrometric properties of the pixelated detector at the cost of lower detection efficiency. This technique can be used for energy sensitive X-ray imaging of inanimate objects where the radiation dose does not present an issue.

Trichobilharzia regenti (Schistosomatidae): 3D imaging techniques in characterization of larval migration through the CNS of vertebrates

Migration of parasitic worms through the host tissues, which may occasionally result in fatal damage to the internal organs, represents one of the major risks associated with helminthoses. In order to track the parasites, traditionally used 2D imaging techniques such as histology or squash preparation do not always provide sufficient data to describe worm location/behavior in the host. On the other hand, 3D imaging methods are widely used in cell biology, medical radiology, osteology or cancer research, but their use in parasitological research is currently occasional. Thus, we aimed at the evaluation of suitability of selected 3D methods to monitor migration of the neuropathogenic avian schistosome Trichobilharzia regenti in extracted spinal cord of experimental vertebrate hosts. All investigated methods, two of them based on tracking of fluorescently stained larvae with or without previous chemical clearing of tissue and one based on X-ray micro-CT, exhibit certain limits for in vivo observation. Nevertheless, our study shows that the tested methods as ultramicroscopy (used for the first time in parasitology) and micro-CT represent promising tool for precise analyzing of parasite larvae in the CNS. Synthesis of these 3D imaging techniques can provide more comprehensive look at the course of infection, host immune response and pathology caused by migrating parasites within entire tissue samples, which would not be possible with traditional approaches.

Wide energy range gamma-ray calibration source

Calibration source with monoenergetic gamma-ray lines in wide energy range designed for gamma-ray detector energetic calibration and testing has been built. Gamma-rays are obtained from thermal neutron capture, which is a suitable and cost efficient way how to provide discrete gamma-ray lines with energies above 3 MeV with reasonable intensity. With appropriate and interchangeable targets the source can generate different gamma-ray spectra with energy up to 10 MeV. We present the data obtained with neutron capture on chlorine, but other elements with high thermal neutron capture cross-section such as chrome, iron, nickel and titanium can be used as well. As neutron source we employ radionuclide sources (252Cf or 241Am-Be) with emission rate about 106 neutrons/s. The emitted fast neutrons are moderated by a moderator made of light materials such as graphite, standard water or heavy water. Performance of the source is demonstrated by calibration spectra measured by HPGe and scintillation detectors (LaBr3, NaI(Tl)).

Geometric correction methods for Timepix based large area detectors

X-ray micro radiography with the hybrid pixel detectors provides versatile tool for the object inspection in various fields of science. It has proven itself especially suitable for the samples with low intrinsic attenuation contrast (e.g. soft tissue in biology, plastics in material sciences, thin paint layers in cultural heritage, etc.). The limited size of single Medipix type detector (1.96 cm2) was recently overcome by the construction of large area detectors WidePIX assembled of Timepix chips equipped with edgeless silicon sensors. The largest already built device consists of 100 chips and provides fully sensitive area of 14.3 × 14.3 cm2 without any physical gaps between sensors. The pixel resolution of this device is 2560 × 2560 pixels (6.5 Mpix). The unique modular detector layout requires special processing of acquired data to avoid occurring image distortions. It is necessary to use several geometric compensations after standard corrections methods typical for this type of pixel detectors (i.e. flat-field, beam hardening correction). The proposed geometric compensations cover both concept features and particular detector assembly misalignment of individual chip rows of large area detectors based on Timepix assemblies. The former deals with larger border pixels in individual edgeless sensors and their behaviour while the latter grapple with shifts, tilts and steps between detector rows. The real position of all pixels is defined in Cartesian coordinate system and together with non-binary reliability mask it is used for the final image interpolation. The results of geometric corrections for test wire phantoms and paleo botanic material are presented in this article.

Mobile system for in-situ imaging of cultural objects

Non-invasive analytical techniques recently developed with the Timepix pixel detector have shown great potential for the inspection of objects of cultural heritage. We have developed new instrumentation and methodology for in-situ X-ray transmission radiography and X-ray fluorescence imaging and successfully tested and evaluated a mobile system for remote terrain tasks. The prototype portable imaging device comprises the radiation source tube and the spectral sensitive X-ray camera. Both components can be moreover mounted on independent motorized positioning systems allowing adaptation of irradiation geometry to the object shape. Both parts are placed onto a pair of universal portable holders (tripods). The detector is placed in a shielded box with exchangeable entrance window (beam filters and pinhole collimator). This adjustable setup allows performing in-situ measurements for both transmission and emission (XRF) radiography. The assembled system has been successfully tested in our laboratory with phantoms and real samples. The obtained and evaluated results are presented in this paper. Future work will include successive adaptation of the current system for real in-situ utilization and preparation of software allowing semi-automatic remote control of measurements.