After passage through matter, the energy spectrum of a polychromatic beam of x-rays contains valuable information about the elemental composition of the absorber. Conventional x-ray systems or x-ray computed tomography (CT) systems, equipped with scintillator detectors operated in the integrating mode, are largely insensitive to this type of spectral information, since the detector output is proportional to the energy fluence integrated over the whole spectrum. The main purpose of this paper is to investigate to which extent energy-sensitive photon counting devices, operated in the pulse-mode, are capable of revealing quantitative information about the elemental composition of the absorber. We focus on the detection of element-specific, K-edge discontinuities of the photo-electric cross-section. To be specific, we address the question of measuring and imaging the local density of a gadolinium-based contrast agent, in the framework of a generalized dual-energy pre-processing. Our results are very promising and seem to open up new possibilities for the imaging of the distribution of elements with a high atomic number Z in the human body using x-ray attenuation measurements. To demonstrate the usefulness of the detection and the appropriate processing of the spectral information, we present simulated images of an artherosclerotic coronary vessel filled with gadolinium-based contrast agent. While conventional systems, equipped with integrating detectors, often fail to differentiate between contrast filled lumen and artherosclerotic plaque, the use of an energy-selective detection system based on the counting of individual photons reveals a strong contrast between plaque and contrast agent.

https://iopscience.iop.org/article/10.1088/0031-9155/52/15/020/pdf

K-edge imaging in x-ray computed tomography using multi-bin photon counting detectors.

The PILATUS 1M detector is a hybrid pixel array detector with over one million pixels that operate in single photon counting mode. The detector, designed for macromolecular crystallography, is the largest pixel array detector currently in use at a synchrotron. It is a modular system consisting of 18 multichip modules covering an area of 21 cm × 24 cm. The design of the components as well as the manufacturing of the detector including the bump-bonding was performed at the Paul Scherrer Institute (PSI). The use of a single photon counting detector for protein crystallography requires detailed studies of the charge collection properties of the silicon sensor. The 18 modules are read out in parallel, leading to a full frame readout-time of 6.7 ms. This allows crystallographic data to be acquired in fine-φ-slicing mode with continuous rotation of the sample. The detector was tested in several experiments at the protein crystallography beamline X06SA at the Swiss Light Source at PSI. Data were collected both in conventional oscillation mode using the shutter, as well as in a fine-φ-slicing mode. After applying all the necessary corrections to data from a thaumatin crystal, the processing of the conventional data led to satisfactory merging R-factors of the order of 8.5%. This allows, for the first time, determination of a refined electron density map of a macromolecular biological crystal using a silicon pixel detector.

https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A16541/datastream/PDF/Broennimann-2006-The_PILATUS_1M_detector-%28published_version%29.pdf

The PILATUS 1M detector.

Charge-coupled device (CCD) area x-ray detector technology is reviewed. CCD detectors consist of a serial chain of signal components, such as phosphors, fiber optics or lenses, image intensifiers and the CCD which serve to convert the x-ray energy to light or electron-hole pairs and to record the spatially resolved image. The various combinations of components that have been used to make CCD detectors are described and the properties of each of the critical components are discussed. Calibration and correction procedures required for accurate data collection are described. The review closes with a brief description of future directions for solid-state area x-ray detectors.

Charge-coupled device area x-ray detectors

Time-resolved experiments in powder diffraction are limited by the long time required to record spectra with current detectors. A major improvement can be made by using a massively parallel X-ray detection system together with a fast read out. The Mythen detector (Microstrip system for time-resolved experiments) has been built for the Powder Diffraction Station of the Material Science beamline at the Swiss Light Source to meet these requirements. The specifically developed read out chip (Mythen chip), the detector system and first measurements are shown.

Mythen detector system

Until recently, structure determination by transmission electron microscopy of beam-sensitive three-dimensional nanocrystals required electron diffraction tomography data collection at liquid-nitrogen temperature, in order to reduce radiation damage. Here it is shown that the novel Timepix detector combines a high dynamic range with a very high signal-to-noise ratio and single-electron sensitivity, enabling ab initio phasing of beam-sensitive organic compounds. Low-dose electron diffraction data (∼0.013 e− A−2 s−1) were collected at room temperature with the rotation method. It was ascertained that the data were of sufficient quality for structure solution using direct methods using software developed for X-ray crystallography (XDS, SHELX) and for electron crystallography (ADT3D/PETS, SIR2014).

/pdf/ab-initio-structure-determination-of-nanocrystals-of-organic-1gkeshnt31.pdf

Ab initio structure determination of nanocrystals of organic pharmaceutical compounds by electron diffraction at room temperature using a Timepix quantum area direct electron detector

For the protein crystallography beamlime of the Swiss Light Source (SLS), which will be operational in summer 2001, the PILATUS detector ( PI xe L A ppara TU s for the S LS) is currently being built. The goal of the PILATUS project is a hybrid pixel system with a size of 40×40 cm 2 having 2000×2000 pixels. The detector will be operated in single photon counting mode for 12 keV X-rays. The prototype pixel read-out chip has a noise of 75 e − with sensor, a low threshold dispersion and a maximum count rate of 1 MHz/pixel. Due to the expected radiation dose in operation at the beamline, the chip is designed in radiation hard DMILL technology.

A pixel read-out chip for the PILATUS project

At the Paul Scherrer Institute a new synchrotron light source is currently under construction, the Swiss Light Source (SLS), which will be operational in summer 2001. Among the first beamlines is a high brightness, micro-focusing protein crystallography beamline. It will be equipped with a pixel detector, which has several features of interest for the next generation of protein crystallography detectors. The point spread function and the effect of charge sharing was measured with a prototype detector in a test experiment at the European Synchrotron Radiation Facility in Grenoble. The concepts of the SLS pixel detector is presented as well as test results from radiation hard prototype chips.

A pixel detector for the protein crystallography beamline at the SLS

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A pixel read-out chip for the PILATUS project

A pixel detector for the protein crystallography beamline at the SLS