Foam-like phantoms for comparing tomography algorithms

Tomographic algorithms are often compared by evaluating them on certain benchmark datasets. For fair comparison, these datasets should ideally (i) be challenging to reconstruct, (ii) be representative of typical tomographic experiments, (iii) be flexible to allow for different acquisition modes, and (iv) include enough samples to allow for comparison of data-driven algorithms. Current approaches often satisfy only some of these requirements, but not all. For example, real-world datasets are typically challenging and representative of a category of experimental examples, but are restricted to the acquisition mode that was used in the experiment and are often limited in the number of samples. Mathematical phantoms are often flexible and can sometimes produce enough samples for data-driven approaches, but can be relatively easy to reconstruct and are often not representative of typical scanned objects. In this paper, we present a family of foam-like mathematical phantoms that aims to satisfy all four requirements simultaneously. The phantoms consist of foam-like structures with more than 100000 features, making them challenging to reconstruct and representative of common tomography samples. Because the phantoms are computer-generated, varying acquisition modes and experimental conditions can be simulated. An effectively unlimited number of random variations of the phantoms can be generated, making them suitable for data-driven approaches. We give a formal mathematical definition of the foam-like phantoms, and explain how they can be generated and used in virtual tomographic experiments in a computationally efficient way. In addition, several 4D extensions of the 3D phantoms are given, enabling comparisons of algorithms for dynamic tomography. Finally, example phantoms and tomographic datasets are given, showing that the phantoms can be effectively used to make fair and informative comparisons between tomography algorithms.

The Development of an Intelligent Zinc Oxide Lighting Arrester Tester

Zinc oxide arrester is often used as lightning protection device in 10KV distribution network. In order to check the reliable operation of the zinc oxide arrester, preventive tests are often carried out. In this project, the intelligent tester adopts high-precision clamp current mutual inductance technology as the front-end acquisition mode of current signals; Magnetic isolation technology is used to ensure the accuracy of current and voltage sampling and the anti-interference ability and testing accuracy of the instrument are improved by using fast Fourier transform for data processing. The integrated application of several technologies provides a basis for judging the operating state of the 10kV zinc oxide arrester. The charged measurement of operating parameters of 10kV zinc oxide arrester is realized and the measurement efficiency is improved.

Paediatric head computed tomography dose values and the impact on image quality

Background The purpose of this study is to analyse paediatric head Computed Tomography (CT) examination dose values, establish local Diagnostic Reference Levels (DRL), and perform objective image quality assessment per categorisation. Methods A total of 100 paediatric head CT examinations divided into 5 paediatric age categorisations were retrospectively selected: 0–3months, 3months to 1 year, 1 to 6 years, and more than 6 years. Computed Tomography Dose Index (CTDIvol - mGy) and Dose Lenght Product (DLP – mGy.cm), acquisition mode and CT scanner were collected per examination. Examinations with lower and higher dose values per categorisation were selected, and 10 Regions of Interest (ROI’s) were defined on supra and infra tentorial regions in order to access image quality, based on signal and noise values. Local DRLs were compare with the literature and with previous studies of this centre. Results The obtained DLP values were 580, 570, 700, 754 mGy.cm, for the categorisation of 0–3 months, 3 months to 1 year, 1 to 6 years, and more than 6 years, respectively. No significant differences were founded in dose values and image quality, per paediatric categorisation. Conclusions Despise previous local DRLs were defined using a different age categorisation, some paediatric aged categorisation revealed an increase of the dose values. These results must be related with the acquisition of a new CT scanner. Optimisation process is on-going and new protocols are being define.

ULTRASONIC ANGLE-DEPENDENT REFLECTIVITY IN COMPLEX ROCKS FOR IMPROVED INTERPRETATION OF SONIC AND ULTRASONIC LOGS

Porous rocks are rarely homogeneous. Significant spatial variations in elastic properties are often observed in rocks due to depositional, diagenetic, and structural processes. In laminated sandstones, complex carbonates, or unconventional formations, elastic properties can vary on scales from millimeters to tens of meters. Detection of inhomogeneities and their size in rocks is crucial for fracture propagation design, height containment assessment, and for improving well/reservoir productivity. Most laboratory techniques used to measure rock elastic properties fail to distinguish mid-scale anisotropy; results are subject to spatial averaging effects. We introduce a new experimental method to measure continuous compressional- and shear-wave logs of core samples based on measurements of angle-dependent ultrasonic reflection coefficients. Simultaneously with reflected waves, we detect and interpret refracted waves as an independent way to estimate acoustic wave velocities to support the analysis. Our laboratory system is equipped with an array of receivers to continuously collect measurements. At each core location, we acquire acoustic waveforms at multiple transmitter-receiver angles using a pitch-catch acquisition mode (similar to standard sonic tools). This acquisition mode uses multiple receivers, allowing us to obtain measurements at different incidence angles without moving the sample and keeping the distance traveled by reflected waves constant, thereby eliminating the need for geometrical spreading corrections in reflection-coefficient calculations. Reflectivity-vs.-angle measurements are then matched with numerical simulations to estimate rock elastic properties. Ultrasonic reflection-coefficient measurements are successfully used to estimate dynamic elastic rock properties of homogeneous and layered rock samples. For homogenous samples, values are within a 5% range when compared to those obtained with the standard acoustic transmission method. Measurements acquired on natural and artificially constructed samples show significant departures from homogeneous behavior caused by layering. Laboratory reflection-coefficient measurements enable detection of inch-scale anisotropy within the rock, leading to improved assessment of formation elastic properties. Furthermore, continuous core measurements provide high-resolution reflection-coefficient information which is complementary to open-hole ultrasonic logs.