There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

J. Appl. Cryst.の発刊に際して

The ability of dual- and multi-energy CT to differentiate materials of different effective atomic numbers makes possible several new and clinically relevant CT applications.

Dual- and Multi-Energy CT: Principles, Technical Approaches, and Clinical Applications

This review (over 380 references) summarizes metal–organic frameworks (MOFs), Materials Institute Lavoisier (MILs), iso-reticular metal–organic frameworks (IR-MOFs), porous coordination networks (PCNs), zeolitic metal–organic frameworks (ZMOFs) and porous coordination polymers (PCPs) with selected examples of their structures, concepts for linkers, syntheses, post-synthesis modifications, metal nanoparticle formations in MOFs, porosity and zeolitic behavior for applications in gas storage for hydrogen, carbon dioxide, methane and applications in conductivity, luminescence and catalysis.

MOFs, MILs and more: concepts, properties and applications for porous coordination networks (PCNs)

Photon counting detectors (PCDs) with energy discrimination capabilities have been developed for medical x-ray computed tomography (CT) and x-ray (XR) imaging. Using detection mechanisms that are completely different from the current energy integrating detectors and measuring the material information of the object to be imaged, these PCDs have the potential not only to improve the current CT and XR images, such as dose reduction, but also to open revolutionary novel applications such as molecular CT and XR imaging. The performance of PCDs is not flawless, however, and it seems extremely challenging to develop PCDs with close to ideal characteristics. In this paper, the authors offer our vision for the future of PCD-CT and PCD-XR with the review of the current status and the prediction of (1) detector technologies, (2) imaging technologies, (3) system technologies, and (4) potential clinical benefits with PCDs.

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Vision 20/20: Single photon counting x-ray detectors in medical imaging

Spectroscopic X-ray imaging enhances image contrast and provides advanced object information due to energy resolution. The Medipix-2 is a photon counting semiconductor detector and features two energy thresholds for spectroscopic imaging. The aim of this study is to present the development of optimized threshold adjustment masks with small energy windows of about 3 keV and to demonstrate spectroscopic X-ray imaging using the example of an integrated circuit.

Optimization of Medipix-2 threshold masks for spectroscopic X-ray imaging

The development of a real-time digital signal processing unit for gamma ray detection is shown. A schematic of the contributing electronic components is illustrated along with the digital and analog specifications. The used digital algorithms for signal processing are presented and compared as well as energy spectra of 137Cs with different detector types, namely CPG CdZnTe and LaBr 3 , derived with an experimental setup.

Development of a GMCA (Gamma analysis digital filter and Multi Channel Analyzer)

Experiments of deposition of CdTe films have been carried out under microgravity in the Russian Foton M3 mission. The influence of gravity has been studied with these experiments and compared to the results of simulations. The measured deposition rate could be confirmed by the theoretical results for lower temperatures. For higher temperatures the measured thickness of the deposited films was larger compared to the theoretical data. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Deposition of CdTe films under microgravity: Foton M3 mission

Spectroscopic micro-computed tomography using photon counting detectors is a technology that promises to deliver material-specific images in pre-clinical research. Inherent to such applications is the need for a high spatial resolution, which can only be achieved with small focal spot sizes in the micrometer range. This limits the achievable x-ray fluxes and implies long acquisitions easily exceeding one hour, during which it is paramount to maintain a constant detector response. Given that photon-counting detectors are delicate systems, with each pixel hosting advanced analog and digital circuitry, this can represent a challenging task. In this contribution, we illustrate our findings on how to reduce image artifacts in computed tomography reconstructions under these conditions, using a Medipix3RX detector featuring a cadmium telluride sensor. We find that maintaining a constant temperature is a prerequisite to guarantee energy threshold stability. More importantly, we identify varying sensor leakage currents as a significant source to artifact formation. We show that these leakage currents can render the corresponding images unusable if the ambient temperature fluctuates, as caused by an air conditioning, for example. We conclude with demonstrating the necessity of an adjustable leakage current compensation.

Reducing the formation of image artifacts during spectroscopic micro-CT acquisitions

The resistivity dependence on Zn concentration had been investigated in semi-insulating (Cd,Zn)Te crystals grown bythe vertical Bridgman method A coorelation between the zinc concentration and the resistivity distribution could befound The obtained resistivity was in the interval of 2 x10 9 -10 10 cm as expected from the model of compensationThe main deep compensating levels detected by Photo Induced Current Transient Spectroscopy (PICTS) were at 064 ±002 eV and close the middle of the band gap at 080 ± 002 eVKeywords: (Cd,Zn)Te, compensation, high resistivity, deep levels 1 INTRODUCTION (Cd,Zn)Te CZT is still the first choice of material for room temperature X- and -ray detectors The common growthtechniques are the conventional vertical Bridgman (VB) and the High Pressure Bridgman (HPB) method Severalreviews present the state of the art of the HPB material by the material properties, the detector performance and theapplications 1-5 Nevertheless, it is very difficult to find a reasonable explanation of this choice of material, because of well knowndifficulties in the growth of CZT, decreasing of its average atomic number, and increasing of the energy threshold forpair creation in comparison with CdTeThere are three reasons to use CZT instead of CdTe:- increasing of the band gap in strong dependence of the Zn concentration- hardening effect- reduced polarization effectThe main interest is the increased resistivity, because of the reduced leakage current and the better signal to noiseperformance Theoretically the resistivity of Cd

Michael Fiederle

Papers

Optimization of Medipix-2 threshold masks for spectroscopic X-ray imaging

Development of a GMCA (Gamma analysis digital filter and Multi Channel Analyzer)

Deposition of CdTe films under microgravity: Foton M3 mission

Reducing the formation of image artifacts during spectroscopic micro-CT acquisitions

Resistivity dependence on Zn concentration in semi-insulating (Cd,Zn)Te